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UP Board Notes for Class 10 Science Chapter 9 Excretion-Elimination of Body Wastes

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Excretion-Elimination of Body Wastes Learning Objectives

After completing this chapter, you will be able to:

  • Define excretion and mention its importance;
  • Describe the nature of excretory wastes produced in our body,
  • Identify different parts of the excretory system and describe their functions; Excretion – Elimination of Body Wastes
  • Describe the gross anatomy of the kidney,
  • Identify the parts of the nephron responsible for urine formation;
  • Explain the physiology of urine formation; describe the mechanism of osmoregulation by the kidney.

Various waste products are formed in our bodies continuously as a result of many metabolic activities taking place inside the body. These waste substances, if accumulated, would poison cells or slow down metabolism. Hence, the body must get rid of these unwanted substances. The metabolic wastes to be excreted include CO₂, H₂O, fats, ammonia, urea, uric acid, etc.

Excretion-Elimination of Body Wastes Excretion

  • The removal of waste products formed in the body as a result of metabolism is termed excretion. Excretion can also be defined as the removal of mainly nitrogenous wastes from the body. The lungs and kidneys are the main organs of excretion in human beings. The process of maintaining the right amount of water and proper ionic balance in the body is called osmoregulation.

Nature Of Excretory Wastes

  • The wastes formed as a result of various metabolic activities are:

1. Respiratory waste formed as a result of oxidation of glucose (food) (through cellular respiration):

  • These mainly constitute carbon dioxide and water.
  • The carbon dioxide is eliminated from the body through the lungs (during expiration).
  • Water becomes a part of the rest of the water contained in the body.

2. Nitrogenous waste formed as a result of deamination of unwanted amino acids, body’s own proteins and nucleic acids: The three main nitrogenous waste products excreted by animals are ammonia, urea and uric acid. Urea is a highly poisonous waste product and its accumulation beyond a certain concentration in the body may cause death. Urea is eliminated through the kidneys.

3. Other waste like salts (NaCl), excess vitamins and water, which we take directly through food: Excess salts are mainly excreted by kidneys.

4. The excess water is removed by kidneys as urine and some of it is excreted as sweat by the sweat glands on our skin.

5. Bile pigments are formed due to the breakdown of haemoglobin in dead RBCs in the liver. A large amount of these pigments is excreted out in faeces while some of it is excreted in the urine.

Excretion-Elimination of Body Wastes Human Urinary System

The urinary system in human beings consists of the following parts.

  1. A pair of kidneys
  2. A pair of ureters
  3. Urinary bladder
  4. Urethra

1. Kidneys

  • The kidneys are reddish-brown, paired structures located on either side of the vertebral column (backbone). They are protected by the last two pairs of ribs. Kidneys in human beings are said to be retroperitoneal because they lie behind the peritoneal lining of the abdominal cavity.
  • Each kidney is a bean-shaped organ, about 10 cm long, 6 cm wide and 4 cm thick. The right kidney is positioned slightly at a lower level than the left kidney as the right side of the abdominal cavity is occupied by the liver. They are held in position by a padding. On the inner concave side of the kidney, a notch called the hilum is present. It is the place from where the ureter and the renal vein come out and the renal artery enters the kidney.

2. Ureters

  • The ureters arise from within the renal sinus of the kidney at hilum. The front end of each ureter is extended into a funnel-shaped structure, the renal pelvis. The ureters transport urine from the kidneys to the urinary bladder. Each ureter opens obliquely in the urinary bladder by a slit-like aperture to prevent the backflow of the urine.

3. Urinary bladder

  • The urinary bladder is a muscular reservoir for storage of urine. It lies in the pelvic cavity of the abdomen. The neck of the urinary bladder is surrounded by sphincters. Sphincter acts like a valve which remain closed until the time of micturition (urination) described below.

Role of the urinary bladder in urination

  • Besides functioning as a temporary reservoir of urine, the bladder also evacuates the urine at suitable intervals. The act of voiding or discharging urine is called micturition.

Excretion-Elimination-of-Body-Wastes-The-human-urinary-system

  • When enough urine gets accumulated in the bladder to raise its pressure sufficiently, a spontaneous nervous activity (reflex) is initiated. This causes the smooth muscles on the bladder wall to contract and the urethral sphincter to relax. Urine flows to the outside. As the ureters enter obliquely through the bladder wall, their openings get shut due to compression by the contracting bladder muscles and backward flow of urine is prevented.

4. Urethra

  • The urethra is a tube that arises from the neck of urinary bladder and extends up to the outside. In males, it serves as a common passage for urine and sperm. The urethra in females serves as a passage for urine only.

Excretion-Elimination of Body Wastes Internal Structure of The Kidney

  • Each kidney in a longitudinal section shows two distinct regions- an outer renal cortex and an inner renal medulla. The medulla is subdivided into 15 or 16 conical masses, the renal pyramids. Due to presence of these pyramids, the medulla has a striped appearance.
  • Each pyramid has a narrow renal papilla toward the pelvis and a broad base toward the cortex. Renal papillae open into a wide funnel-like structure, renal pelvis. The renal pelvis in turn leads into the ureter.

Excretion-Elimination-of-Body-Wastes-The-structure-and-location-of-nephron-in-a-kidney

Nephron – structural and functional unit of kidney

  • Each kidney consists of more than one million nephrons or uriniferous tubules. Nephron is the functional unit of a kidney. Each nephron consists of – a Malpighian capsule, a nephric tubule (secretory part of uriniferous tubule) and a collecting tubule.

Structure of Malpighian capsule

  • It has two parts a Bowman’s capsule and a glomerulus.
  1. Bowman’s capsule: It forms the dilated blind end of the nephron. It is a double-walled, cup-shaped structure. It is lined by a thin semipermeable squamous epithelium. The outer concavity of Bowman’s cup contains a knot-like mass of blood capillaries called glomerulus.
  2. Glomerulus: The afferent arteriole enters the Bowman’s capsule and divides into a bunch of about 50 capillaries. This bunch is called glomerulus. Their diameter gets reduced to increase the blood pressure. Bowman’s capsule together with the glomerulus are called renal capsule or Malpighian capsule.

Nephric or uriniferous tubule

  • It is a long, coiled tubule and can be divided into three major -regions the proximal convoluted tubule (PCT), the loop of Henle and the distal convoluted tubule (DCT).
  1. Proximal convoluted tubule (PCT): It is the initial (proximal) convoluted region of the nephric tubule nearer to the Bowman’s capsule. It is a highly coiled structure and is about 12-24 mm in length. It is lined by the columnar epithelium and is provided with microvilli. PCT is located in the cortex region of kidney.
  2. Loop of Henle: It is a U-shaped loop formed in the middle of the nephric tubule. It has a thin descending limb and a thick ascending limb. The descending limb is lined with flattened epithelial cells, while the ascending limb is lined with cuboidal epithelium. It is not convoluted. It runs in the medulla and turns back to cortex region.
  3. Distal convoluted tubule (DCT): It is a convoluted structure and is present in the cortex region. It is lined by cuboidal epithelium. It opens into the collecting tubule.

Collecting ducts and the ducts of Bellini

  • Collecting ducts are larger ducts, each receiving collecting tubules from nephrons. These pass into the renal medulla and join with each other forming still larger ducts of Bellini. These ducts drain the urine collected from the nephrons into the renal pelvis which leads to the ureter.

Blood supply to kidney tubules

  • Each kidney receives blood supply from renal arteries branching off from dorsal aorta. These arteries further branch off into arterioles and each arteriole, called afferent arteriole, enters inside Bowman’s capsule.
  • It branches further and forms a mass of capillaries called glomerulus. The fine capillaries of glomerulus reunite and form efferent arteriole. Efferent arteriole comes out of Bowman’s capsule and surrounds renal tubule. They further rejoin and form renal veins which kidney and empty into posterior vena cava.

Excretion-Elimination of Body Wastes Physiology of Urine Formation

  • Urine formation involves three main processes – ultrafiltration, tubular reabsorption and tubular secretion.

1. Ultrafiltration

  • Walls of glomerular capillaries and Bowman’s capsule are very thin and semipermeable in nature. Hence, they act as ultrafilters.
  • The glomerular hydrostatic pressure or the capillary pressure is the main driving force that tends to move fluid out of the glomeruli. It is exerted by the blood while passing through the glomerulus.

Why is hydrostatic pressure more in glomerulus?

  • The afferent arteriole entering the Bowman’s capsule is wider than the efferent arteriole leaving it. As a result, more blood enters the glomerulus while less blood moves out. This is the reason behind the high hydrostatic pressure in the glomerulus.
  • Due to this high filtration pressure in the blood of glomerulus, a part of water and dissolved constituents of blood (like nitrogenous wastes, glucose, amino acids, mineral ions, etc.), are filtered out in the Bowman’s capsule. This forms the glomerular filtrate. Filtration under high pressure is called ultrafiltration.

Excretion-Elimination-of-Body-Wastes-Filtration-in-the-glomerulus-(ultrafiltration)

  • During ultrafiltration, nearly all the liquid components of blood come out of glomerulus and pass into the funnel of Bowman’s capsule. The rest of the blood, left behind in the glomerulus after ultrafiltration is very thick (because the liquid part has been removed) and is carried forward by the efferent arteriole.
  • The glomerular filtration rate in adults is 120 mL per minute and the filtrate produced daily amounts to about 172 litres.

2. Tubular reabsorption or selective reabsorption

  • Our body cannot afford to lose several useful substances that are filtered in the glomerular filtrate. As this filtrate flows through the nephric tubule, water and several useful substances (solutes) are reabsorbed through the wall of the renal tubule (nephric tubule) and returned to the blood flowing in peritubular capillaries. This is called selective reabsorption.
  • Water is reabsorbed by osmosis. Selective reabsorption of glucose, amino acids and salts also take place.

Excretion-Elimination-of-Body-Wastes-Role-of-nephron-in-urine-formation

  • In the PCT, 65-80 per cent of the filtrate is reabsorbed. It includes water, glucose, amino acids and minerals like Na+, K+ and Ca++.
  • In the descending limb, 5 per cent water is reabsorbed.
  • In the ascending limb, only minerals (Na+, K+, Cl-) are reabsorbed. The ascending limb is impermeable to water.
  • In the DCT and collecting ducts, Nat is reabsorbed under the influence of hormone aldosterone and water is reabsorbed under the influence of hormone ADH (antidiuretic hormone).

3. Tubular secretion

  • This process is the converse of tubular reabsorption. The cells of the renal tubule also remove wastes from blood and pass into the filtrate by the process of secretion. Tubular secretion removes ammonia, urea, uric acid, creatinine and hippuric acid from the blood. The function of various parts of renal tubule in formation of urine are given in Table.
  1. Blood from renal artery enters kidneys.
  2. Ultrafiltration: Blood enters glomerular capillaries. Water and small solutes are filtered in Bowman’s capsule.
  3. Tubular reabsorption: Water and many solutes are reabsorbed through the wall of nephric tubule and return to the blood in peritubular capillaries.
  4. Tubular secretion: Cells of renal tubule remove wastes from blood and pass them into filtrate.
  5. Hormonal action adjusts the urine. concentration. ADH promotes water reabsorption. Aldosterone influences reabsorption of sodium and potassium.
  6. Urination: Water and solutes flow to renal pelvis, then eliminated out through urinary tract.Excretion-Elimination-of-Body-Wastes-Function-of-various-parts-of-renal-tubule-in-urine-formation

Excretion-Elimination of Body Wastes Hormonal Control Of Urine Formation

  • Urine formation is under the control of two hormones – antidiuretic hormone (ADH) and aldosterone.
  1. Antidiuretic hormone (ADH) or vasopressin released from the posterior lobe of pituitary gland, increases the permeability of the renal tubule to water. When the blood plasma is concentrated, more ADH is secreted and more water is reabsorbed in the urinary tubules. Hence, urine passed out from body is concentrated, for example in summer. When the blood plasma is diluted, less ADH is secreted and less water is reabsorbed in the urinary tubule. In this case, a large amount of dilute urine is passed out of the body, for example in winter.
  2.  Aldosterone, a hormone released from the adrenal cortex, influences reabsorption of sodium and potassium. This hormone regulates the amount of sodium and potassium that is to be retained in the blood and is to be excreted.

Urine And Its Composition

  • An adult man normally passes about 1-1.5 litres of urine in a day. Urine is a transparent yellowish fluid. Its yellow colour is due to a pigment urochrome derived from the breakdown of haemoglobin of worn-out RBCs,
  • Its pH range is 5-8. It has an unpleasant odour. If allowed to stand, the urea present in urine is degraded by bacteria to ammonia, which gives a strong awful smell to it.
  • In normal composition, urine consists of 95 per cent water, and rest 5 per cent is the organic and inorganic substances (solid wastes). Each litre of urine contains nitrogenous organic compounds – urea 2.3 g, uric acid 0.7 g, creatinine 1.5 g and a negligible amount of hippuric acid. Of these, urea is the principal nitrogenous waste in human urine. The non-nitrogenous organic compounds include vitamin C, oxalic acid and phenolic substances.
  • The inorganic substances include ammonia (0.6 g/L) and mineral salts, such as phosphates, sulphates and chlorides of Na, K, Ca and Mg. Sodium chloride (9.0 g/L) is the principal mineral salt in the urine.
  • Abnormal components of urine include albumin, bile salts, bile pigments, glucose and ketone bodies, which occur in the urine in various pathological conditions.

Excretion-Elimination-of-Body-Wastes-The-process-of-urine-formation

Common diseases related to abnormal composition of urine

  • Glycosuria: Urine with high glucose due to diabetes mellitus
  • Albuminuria: Urine with albumin due to high blood pressure
  • Ketonuria: Urine with ketone body
  • Jaundice/Hepatitis/Liver cirrhosis: Urine with bile pigment
  • Pyuria: Urine with pus cells
  • Haematuria: Urine with blood cells due to urinary tract infection or kidney stone
  • Diabetes insipidus: Urine with excess of water (frequent passing out of large quantities of urine) due to deficiency of ADH or vasopressin

Role ADH and insulin in urine

  • The hormone vasopressin or antidiuretic hormone (ADH) regulates the output of urine. This hormone is secreted by the posterior lobe of the pituitary gland. When the secretion of this hormone gets reduced, the amount of urine produced is increased, causing diabetes insipidus disorder. Sometimes hyposecretion of the insulin hormone causes diabetes mellitus disease in which excess glucose is passed with urine.

Excretion-Elimination of Body Wastes Osmoregulation By The Kidney

  • The water and solute content of body fluids is regulated by the kidney. This function of the regulation of osmotic concentration of the blood by the kidney is called osmoregulation.
  • In human beings, the kidney is extremely flexible in its working. Generally, in summer when most of water is lost from the body by perspiration, the urine passed out is hypertonic.
  • However, in winter as there is no perspiration, the urine passed out is hypotonic. This flexibility in the working of human kidney and renal tubules is brought about by the movement of water and Na+ in and out of nephron under the influence of certain hormones, thus osmolarity is regulated.

When there is excess of water in body fluids

In such a condition, the urine passed out of the body is more dilute (hypotonic) than the body fluids. It is achieved by two processes:

  • Excess of water increases blood volume which increases the hydrostatic pressure in glomerulus, hence, more nephric or glomerular filtrates are formed.
  • The sensation of excess of water in the body fluid is received by osmoregulator cells in the hypothalamus part of the brain.
  • These cells in turn influence the posterior lobe of the pituitary gland to inhibit or reduce the release of antidiuretic hormone (ADH). A deficiency of ADH reduces the permeability of cells in the distal convoluted tubule and collecting duct, thereby decreasing the real notion of water.
  • More filtration and less reabsorption of water produce excessively dilute urine. This brings down the volume of the body fluids to normal.

If the body fluids fall below normal

  • During summer, due to excessive sweating, more water is lost, the body fluids reduce. As a result, more and more water is reabsorbed by kidney tubules back into the blood and urine turns thick and yellow. To maintain water balance of the body, the following changes take place in the body.
  • The glomerular filtration slows down due to decreased filtration pressure in the glomerular capillaries.
  • The osmoreceptor cells of the hypothalamus send impulses to the posterior pituitary lobe to release ADH. ADH increases the reabsorption of water in the distal convoluted tubule and the collecting duct by making them more permeable to water.
  • Less filtration and more reabsorption of water leads to the discharge of small amounts of hypertonic urine. This raises the volume of body fluids to normal.

Urine is slightly thicker in summer than in winter

  • During summer, when the temperature is high, lot of water is lost from the body through sweating (perspiration). To make up for this loss, more and more water is reabsorbed by the kidney tubules and put back into the blood making urine more concentrated (thicker).

Why do we feel thirsty despite drinking water at regular intervals?

  • If enough quantity of ADH is not released, water cannot be retained by the kidney tubule and is lost as urine. This causes increase in thirst. Whatever water we drink is lost again. In severe conditions, it causes dehydration and electrolyte imbalance in the body.

Excretion-Elimination of Body Wastes Renal Failure And Artificial Kidney

  • Artificial kidney is used to filter the blood of a patient whose kidneys are damaged. The patient is said to be put on dialysis and the process of purifying blood by an artificial kidney is called haemodialysis.
  • Artificial kidney is a dialysis machine that contains a number of tubes, suspended in dialysing fluid. The patient’s blood is passed through these tubes. During this process, nitrogenous waste products from the blood pass into dialysing fluid. The purified blood is pumped back into the patient’s body.

Excretion-Elimination of Body Wastes Summary

  • The removal of waste products formed in the body due to metabolic activities is termed excretion.
  • Kidneys in human beings are said to be retroperitoneal because they lie behind the peritoneal lining of the abdominal cavity.
  • Each kidney In longitudinal section shows two distinct regions an outer renal cortex and an inner renal medulla.
  • Nephron is the functional unit of kidney.
  • Each nephron consists of a Malpighian capsule, anephric tubule and a collecting tubule.
  • Urine formation involves three main processes ultrafiltration, tubular reabsorption and tubular secretion.
  • Yellow colour of the urine is due to the presence of a pigment, urochrome, derived from the breakdown of haemoglobin of worn-out RBCs.
  • The water and osmotic concentration of blood is maintained by the kidney. This phenomenon is known as osmoregulation.
  • The process of purifying blood by the use of an artificial kidney is called dialysis.

UP Board Notes for Class 10 Science Chapter 10 Nervous System

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Nervous System Learning Objectives

After completing this chapter, you will be able to:

  • State the functions of the nervous system;
  • Describe the structure of a neuron, list its various types and state their specific functions;
  • Describe the transmission of nerve impulses across a synapse,
  • Categorize nervous sytem into central and peripheral nervous systems;
  • List the parts of CNS and state their functions;
  • Describe the structure of the brain and the spinal cord and explain their functions;
  • Describe the structure and functions of peripheral nervous system;
  • Differentiate between sympathetic and parasympathetic nervous systems.

We perform many activities consciously or unconsciously, for example, when we eat food, our eyes help to locate the food, the nose smells it, hands bring the food to the mouth, teeth chew and masticate it, the tongue pushes the food inside the alimentary canal, and so on. All these activities occur in a coordinated manner. The organ system in our body, which brings about coordination and integration of body activities is the nervous system. In this chapter, you will learn about the nervous system in the human body.

Major Divisions of Nervous System

  • The nervous system in human beings is divided into two main parts.
  1. Central nervous system (CNS): It includes the brain and the spinal cord, and is the site of information processing in the nervous system.
  2. Peripheral nervous system (PNS): It consists of nerves that emerge and enter the brain and spinal cord and run between the CNS and different parts of the body. These nerves are divided into three groups sensory or afferent nerves that transmit information to the CNS, motor or efferent nerves that carry messages from the CNS to the effector organ, and mixed nerves.
  • The PNS is further divided into two sub-divisions:
  1. The somatic nervous system (SNS) regulates voluntary activities and transmits messages to the skeletal muscles.
  2. The autonomic nervous system (ANS) works independently to regulate involuntary activities. It consists of nerves and ganglia which connect the visceral organs like smooth muscles of heart, lungs, digestive tract and other internal organs and perform a variety of involuntary actions that are not under the control of our will.
  3. It has two components, viz. sympathetic and parasympathetic, which are antagonistic (opposite) to each other in their functions. You will learn about the autonomic nervous system in a later section.
  • The broad organization of nervous system in humans is shown in Let us first learn about nerves and functioning of the nervous system before discussing about the two divisions of nervous system.

Nervous System Nerves

  • Nerves are composed of nerve fibers (axons) of separate neurons bundled together like the wires of a telephone cable enclosed by a tubular sheath. These nerve fibers or nerve cells are called neurons which form the basic unit of the nervous system. A neuron

Nervous-System-Organization-of-the-nervous-system-in-human-beings

Nervous System Structure of the human nervose system

 

  • is the longest cell in the body. It receives information and transmits it from one part of the body to another part. Thus, a neuron is the structural and functional unit of nervous system and is highly specialized for responding to stimuli.
  • Messages are conducted by nerves in the form of electrical impulses.

Types of Nerves

  • There are three types of nerves depending upon the direction in which they transmit the impulse.
  1. Sensory nerves: These are also called afferent nerves (afferent: carry toward). These nerves contain sensory fibers which carry messages (impulses) from sensory receptors (in sense organs) toward the brain or spinal cord. Example: Optic nerve from eye leading to brain.
  2. Motor nerves: These are also called efferent nerves (referred: to carry away). The nerves contain motor fibers which take messages away from the brain or spinal cord towards the effector organ (such as muscles and glands). Example: Nerves arising in rain and leading to the muscles of the eyeballs for rotating it.
  3. Mixed nerves: These nerves comprise both sensory and motor nerve fibers. Example: Most cranial and spinal nerves are mixed nerves.

Ganglia (singular: ganglion)
These are the aggregate of nerve cells from where the nerve fibers arise.

Structure of a Nerve Cell (Neuron)

  • Each nerve cell consists of three main parts.
  1. Cell body or cyton
  2. Dendrites
  3. Axon

1. Cell body: The cell body or cyton (or Perikaryon) has a large, central nucleus surrounded by the granular cytoplasm. The cytoplasm contains (also called neoplasm) Nissl granules and neurofibrils. It has all the cell organelles (like mitochondria, Golgi apparatus, endoplasmic reticulum, microfilaments, and microtubules). There is no centrosome in the cyton because the nerve cells have lost the ability to divide.

Nervous-System-A-nerve-cell-or-neuron

2. Dendrites (dendron: tree): These are short, thread-like branches which arise from the cell body. The dendrites conduct nerve impulses to the cyton.

3. Axon: One of the branches (of dendrites) grows very long in comparison to others. This branch is called the axon. The axon is covered on the outside by three layers.

  • Axolemma (the innermost layer)
  • Myelin sheath or medullary sheath (the middle layer)
  • Neurolemma (the outermost white insulating sheath)

The axolemma and neurotrauma are continuous sheaths, whereas the myelin sheath is not a continuous one. The myelin sheath shows gaps across its length at intervals. These gaps are known as nodes of Ranvier. The axon ends have swollen bulb-like ends which store acetylcholine (a neurotransmitter). These are called axon endings. Axon endings are closely placed near the dendrites of another neuron but are not connected. Such gaps in between are called synaptic clefts or synapses.

Synapse

  • The neurons are not attached to each other. There is a small gap between them. The fine gap or loose connection between the axon endings of one nerve cell and cyton or dendrite of the next nerve cell is called the synapse. We can also say that the point of contact between two neurons is known as synapse. Signals travel from one neuron to another neuron across these junctions.

Structure of the synapse

The neurons do not touch at the synapse. The space between adjacent neurons is called the synaptic cleft.

  • The axon terminal of a presynaptic neuron has a bulb-like appearance known as a synaptic bulb  The transmission.
    across synapses is done by chemical means. The synaptic bulb contains chemicals known as neurotransmitters.
  • When a nerve impulse (action potential) arises at the axon terminal, it causes synaptic bulbs to release neurotransmitters in the synaptic cleft. chemical transmitter
  • These neurotransmitters diffuse easily across the synaptic cleft. In this way, the impulse is transmitted from one nerve cell to another nerve cell.
  • There are many neurotransmitters but the principal ones are acetylcholine and norepinephrine.Nervous-System-Structure-of-the-synapse

What does a synapse do?

  • Allows information to pass from one neuron to another.
  • Ensures that the nerve impulse travels in one direction only.
  • Allows the adjoining neuron to be excited or inhibited.
  • Amplifies a signal (makes it stronger).
  • Helps in information processing by adding together the effects of all impulses received.
  • Filters out low-leveled stimuli.

There are three types of neurons:

  1. Sensory neurons: These carry impulses from sense organs to the brain or spinal cord.
  2. Motor neurons: These carry impulses from brain or spinal cord to effector organs (muscle or gland).
  3. Association neurons: These interconnect sensory and motor neurons.

Nervous System Communication Through The Nerve – Nerve Impulse

The nervous system receives a stimulus through a receptor organ, integrates or coordinates it, and effects a response through the effector organ. Thus, coordinated behavior has six main components – stimulus, receptor, impulse, coordinator, effector, and response.

  • In such a coordinated behavior, any stimulus of sound, sight, smell, etc., is perceived by receptor organs like eyes, ears, skin, etc.
  • A stimulus is an agent or sudden (external or internal) change that results in a change in the activities of an organism.
  • An impulse is a wave of chemical disturbance that travels through the nerve cell.
  • Receptors are sensory organs that receive stimulus and send waves in form of impulses towards CNS (coordinator).

Nervous-System-Components-of-coordinated-behavior

  • Effectors are the muscles or organs which show response due to motor nerves. Response is a change that occurs in an organism due to a stimulus.
  • The brain and spinal cord are the coordinators that receive information in the form of messages called nerve impulses, from receptor organs via neurons. The information flows to the effector organs, i.e. muscles, which contract or relax or secrete substances to show response.

Nervous-System-Flow-chart-showing-direction-of-nerve-impulse

Transmission of the nerve impulses

  • Nerve impulses pass along a neuron in one direction only. At one end, the neuron is connected to a sensory receptor that receives the stimulus and converts it into electrochemical waves which are carried by the neuron. The nerve fiber at this stage is said to be excited.

Nervous-System-Transmission-of-nerve-impulse-through-a-synapse

  • The events that take place during the conduction of an impulse along a nerve are given as follows.

At resting state – Polarised state

At normal (resting) state, the outer side of the nerve fibers carries more positive (+) charge due to more Na* ions outside the axon membrane. This is called a polarised state.

Nervous-System-Polarised-state-of-nerve-fiber

At stimulated (excited) state – Depolarisation

  • On receipt of a stimulus, the axon membrane at the place of stimulus becomes more permeable to Na+ ions and as a result, the Na* moves inside causing loss of polarity, i.e. depolarization. This region, thus, becomes an exciting region. This region of depolarisation moves forward to next area which in turn becomes depolarised.

Nervous-System-Depolarisation-of-nerve-fibre

Returning to normal state – Repolarisation

  • The previous area (which has received stimulus) becomes repolarised due to active transport of Nat ions outside. This transport is achieved by sodium pump for which energy in the form of ATP is required. Thus, conduction of nerve impulses is a wave of depolarisation followed by repolarisation.

Nervous-System-Transmission-of-nerve-impulse

Central Nervous System

  • The central nervous system consists of the brain and The spinal cord.

The human brain

  • The human brain is a highly developed organ and is situated in the cranium (brain box) of the skull. In an adult, it weighs about 1200-1400 g, about 2% of body weight.

Covering of brain (Meninges)

  • The brain is covered on the outside by membranes called meninges (singular: menix ). Meninges are protective coverings of the brain which consist of three layers.

Nervous-System-Parts-of-the-human-brain

Meningitis

The inflammation (swelling) of the meninges is known as meningitis.

  • The outer tough, protective layer dura mater is formed of fibrous tissue.
  • The middle arachnoid layer is a delicate membrane which gives a web-like cushion.
  • The inner thin, transparent, and highly vascular layer the pia mater. It is richly supplied by blood.

The cerebrospinal fluid

  • It is the watery fluid which fills the spaces between the meninges and also brain cavities or the ventricles. It also acts like a cushion to protect brain from shocks.

Parts of the brain

  • The human brain is divisible into three major parts
  1. Forebrain
  2. Midbrain
  3. HindbrainNervous-System-Divisions-of-the-human-brain-and-their-components

Nervous System Forebrain

  • It is the anterior region of the brain. It has the following parts:
  • Cerebrum (seat of intelligence, memory, consciousness, and voluntary action)
  • Diencephalon (thalamus, hypothalamus, pineal and pituitary glands)

1. Cerebrum (L. cerebrum: brain)

The cerebrum is the main part of forebrain.

  • Cerebrum is the largest and the most prominent part of the brain. It is divided into two halves – the right and left cerebral hemispheres.
  • The two hemispheres are connected by a thick band of nerve fibers called corpus callosum. Corpus callosum helps in the transfer of information from one hemisphere to another.Nervous-System-Different-regions-of-the-brain-are-associated-with-different-functions
  • Each hemisphere is hollow internally and its walls have two regions an outer cortex and an inner medulla. The outer portion or region of the cerebrum (cerebral cortex) contains cell bodies of neurons and is called grey matter (due to its greyish in color).
  • The layer of grey matter is highly convoluted in appearance with ridges and grooves. The fold of ridges are called gyri (singular: gyrus) and depressions (grooves) between them are called sulci (singular: sulcus). The ridges and grooves increase the surface area for more nerve cells.
  • The number and pattern of convolutions in the cerebrum are associated with the degree of intelligence.
  • The inner region of the cerebrum consists of white matter that has axons of nerve cells.

Functions of cerebrum

  • Because of highly developed grey matter the cerebrum governs mental abilities like thinking, reasoning, learning, memory, and intelligence.
  • It also controls all voluntary functions; willpower, emotions, and speech.
  • It enables us to observe things around us through sense organs.
  • It also controls feelings of love, admiration, and hatred. Centers for subconscious mind are also located in the cerebrum. Overall the cerebrum is the seat of intelligence, memory, and willpower.

2. Diencephalon

  • The diencephalon mainly consists of the pineal gland, pituitary gland, thalamus, and hypothalamus. It encloses a cavity called the third ventricle. The thalamus is a relay station for sensory impulses going to the cerebrum. The hypothalamus is situated at the floor of the brain and helps in thermoregulation.

Nervous System Functions of diencephalon

  • The diencephalon contains reflex centers for muscular and glandular activities. It also has centers of emotions, hunger, and thirst. It also helps in controlling the body temperature (thermoregulation) and water-salt balance in the body (osmoregulation).

Midbrain

  • It is a thick-walled structure and is a smaller portion of the brain. The midbrain or mesencephalon connects the anterior region of the brain to the posterior region and therefore all nerve fibers pass through this region. On the dorsal side of the midbrain lie optic lobes which control vision.

Hindbrain

  • The hindbrain has three main parts.
  1. Cerebellum
  2. Pons
  3. Medulla oblongata

1. Cerebellum (Little brain)

  • The cerebellum is situated in the dorsal region. of the hindbrain. Cerebellum is a much smaller area and is located at the base under the large cerebrum.
  • There are no convolutions, but many furrows.
  • It has an outer cortex made of grey matter and an inner section consisting of white matter.

Functions of cerebellum

  • It maintains body balance and controls muscular activities. It makes the body movements smooth, steady, and coordinated. It regulates and coordinates contraction of skeletal muscles.

2. Pons

  • Pons forms the part of the brain stem at the floor of the hindbrain. It is a bridge of transverse nerve tracts extending from the cerebrum to the cerebellum. It also connects the forebrain to the spinal cord.

3. Medulla oblongata

  • The medulla oblongata is the third main part of the hindbrain. It is the lowermost part of the brain located at the base of the skull. It is continued as spinal cord in posterior region.

Functions of medulla oblongata

  • It contains vital reflex centers, such as cardiac center, respiratory center, and centers for swallowing,\ sneezing, and coughing. Thus, it controls involuntary functions of the body like a heartbeat, swallowing, and breathing.
  • Injury to medulla oblongata may lead to death
    Medulla oblongata is main part of the hindbrain. It controls vital reflex centers and Involuntary functions like heartbeat, breathing, and swallowing of food. Any Injury to medulla oblongata will affect these functions and may cause death due to stopping of the heartbeat and breathing.

Nervous-System-Main-functions-of-various-parts-of-the-brain

Nervous System Spinal Cord

  • The spinal cord is a cylindrical, long cord which arises from the medulla oblongata and runs along the vertebral column. It passes through the neural canal of the vertebral column. Like the brain, it is also protected by the three meninges, cerebrospinal fluid, and a cushion of adipose tissue.
  • In the transverse section of spinal cord, a central canal can be seen. This canal is filled with cerebrospinal fluid. Immediately surrounding the canal are clusters of cytons which form the grey matter. In the peripheral part, axons are concentrated and this area is called the white matter.
  • On each side of the spinal cord, there are two horns, the dorsal horn, and the ventral horn. The dorsal root ganglion contains the cell bodies of sensory neurons. A nerve joined to the dorsal horn or dorsal root ganglion picks up sensations from various organs. It is called the sensory nerve.
  • The ventral root contains the axons of large motor neurons. The cell bodies of these motor neurons are located in the spinal cord. Thus, from the ventral horn or ventral root, the motor nerve arises which takes the messages from the spinal cord to the organs concerned.

Nervous-System-structure-of-the-spinal-cord
Nervous-System-components-of-reflex-arc

Functions of the spinal cord

  • It is the center for reflex actions. The spinal cord conducts reflexes below the neck.
  • It conducts sensory impulses from skin and muscles to the brain.
  • It conducts motor responses from brain to the muscles of trunk and limbs.

Reflex Arc And Reflex Action

  • There are certain body responses that are immediate and do not require any processing by the brain. These responses or actions are controlled by the spinal cord. These are called reflex actions.
  • A reflex action may be defined as a spontaneous, automatic, and mechanical response to a stimulus controlled by the spinal cord without the involvement of the brain.
  • The pathway followed by sensory and motor nerves in a reflex action is called the reflex arc.

Components of a reflex arc

  • A reflex arc has four main components.
  1. Receptor or sensory organ to perceive the stimulus.
  2. Sensory or afferent nerve that carries the message from receptor to the spinal cord.
  3. Relay or association neurons of the spinal cord that transmit impulses from the afferent (sensory) neurons to the efferent (motor) neurons.
  4.  Motor or efferent nerve that carries the message from the spinal cord to the muscles or glands (effector organ).
  • The entire sequence of events that constitute a reflex arc are summarized in.

Nervous System Reflexes

  • There are mainly two types of actions – voluntary actions and involuntary actions.
  • Voluntary actions are those actions which are performed consciously. For example, if you wish to play, or switch on TV to watch some programs are voluntary actions.

Nervous-System-Sequence-of-events-in-a-reflex-arc

  • Involuntary actions are those actions that occur unknowingly without our will. For example, you withdraw your hand when it accidentally touches a hot iron; or you start shivering if it is too cold or you start sweating when it is too hot. All involuntary actions are reflexes and involve some kind of sensory stimulation. Differences between voluntary and involuntary actions are given in Table.

Nervous-System-Differences-between-voluntary-and-involuntary-actions

Types of Reflexes

  • There are two types of reflexes:
  •  Simple or natural reflexes
  •  Conditioned or acquired reflexes

1. Simple or natural reflexes are those reflexes that do not require any previous learning experience. Such reflexes are inborn and inherited from parents.

Some examples of simple reflexes are:

  • Blinking of eyelids in response to a foreign particle that approaches the eye.
  • Closing of the eyelid in response to a strong beam of light being flashed on the eyes.
  •  Withdrawal of the leg, if you suddenly step on a nail.
  • Knee-jerk response, if a sharp tap is made below the kneecap, then the leg is involuntarily extended.
  • Sneezing when any irritant enters the nose.
  • Coughing when the swallowed food wrongly enters the windpipe. Immediate withdrawal of hand, if suddenly pricked by a thorn or after touching a hot object.
  • Peristaltic reflex to allow movement of food (chyme) when intestine becomes full and distended.

2. Conditioned or acquired reflexes are those which develop due to some previous experience or training. The conditioned reflexes are not inborn and result due to some learning in one’s lifetime.

Some examples of conditioned reflexes are:

  • Watering of mouth (salivation) at the sight of tasty food.
  • Applying sudden brakes of your bicycle if someone suddenly comes in front.
  • Typing on the keyboard of a computer.
  • Playing a musical instrument such as guitar.
  • Surfing the channels while watching the television.
  • Tying one’s shoelace.
  • The hand signal automatically shows direction to turn the cycle without thinking.Nervous-System-Differences-between-simple-and-acquired-(or conditioned)-reflex

Peripheral Nervous System

  • The peripheral nervous system (PNS) comprises the nerves that connect the central nervous system with different parts of the body.
  • Peripheral nervous system is divided into two subdivisions- somatic nervous system and autonomic nervous system.

1. Somatic nervous system

  • The somatic nervous system includes both motor neurons and sensory neurons. The fibres of motor and sensory neurons are bundled together into nerves, which are of two types.

Nervous-System-Autonomic-nervous-system-showing-sympathetic-and-parasympathetic-divisions

  • Cranial nerves connected directly to the brain, such as the optic nerve (for eye), auditory nerve (for ears), mixed nerves (for face), etc. There are 12 pairs of cranial nerves.
  • Spinal nerves emerge from the spinal cord. There are 31 pairs of spinal nerves. Every spinal nerve is a mixed nerve having both sensory and motor nerves.
  • The somatic nervous system regulates voluntary activities while the autonomic nervous system performs a variety of functions that are not under the control of an individual.

2. Autonomic nervous system
The autonomic nervous system (ANS) includes a chain of 22 pairs of ganglia that lie close to the spinal cord and are associated with the organs they control. ANS is primarily a motor system consisting of neurons that control the functioning of many organs.

  • Heart muscles
  • Glands
  • Smooth muscles (muscles of blood vessels, digestive, respiratory, and reproductive tracts) The ANS can stimulate or inhibit the activity of its target organs. The ANS is divided into two divisions -sympathetic and parasympathetic nervous systems.
  • These two divisions are anatomically and functionally distinct. The sympathetic fibers arise from the thoracic (chest) and lumbar (waist) region of the spinal cord, whereas the parasympathetic fibers arise from the brain and the sacral (pelvic) region of the spinal cord.
  • The effect of the two systems is antagonistic. In general, the sympathetic system stimulates a particular function and prepares the body for violent actions against unusual emergency conditions, while the parasympathetic system has an inhibitory or calming down effect, i.e. it re-establishes normal conditions after the violent action is over. The major differences between sympathetic and parasympathetic nervous systems are given in Table.

Nervous-System-Effect-of-sympathetic-and-parasympathetic-nervous-systems-on-major-organs

Nervous System Summary

  • The nervous system in humans is divided into two parts: central nervous system and peripheral nervous system.
  • The central nervous system includes the brain and the spinal cord and is the site of information processing in the nervous system.
  • The peripheral nervous system consists of nerves that run between central nervous system and different parts of the body.
  • The structural and functional unit of the nervous system is a highly specialized cell called a nerve cell or neuron. Each neuron has three principal parts – the cell body or cyton, the axon, and dendrites.
  • Nerves can be sensory, motor, or mixed.
  • The nervous system receives a stimulus through a receptor organ, integrates or coordinates it, and effects a response through the effector organ.
  • The human brain has three main divisions the forebrain comprising of cerebrum and diencephalon, the midbrain, and the hindbrain comprising of the cerebellum, pons, and medulla oblongata.
  • The cerebrum is the largest and the most prominent part of the brain. It has ridges and grooves (girl and sulci) which increase surface area for nerve cells. The outer cortex of cerebrum contains grey matter. Cerebrum governs mental abilities like thinking, reasoning, learning, memorizing, intelligence, will, and emotions. lotions.
  • Cerebellum is the smaller part located at the base under the large cerebrum. It maintains body balance and controls postures and coordinates muscular activities.
  • Medulla oblongata is the lowermost part of the brain located at the base of the skull. It contains vital reflex centers and controls the activities of the internal organs.
  • The spinal cord is a long cord that arises from the medulla oblongata and runs along the vertebral column.
  • Reflex action is a spontaneous, automatic, and mechanical response to a stimulus controlled by the spinal cord without the involvement of the brain. Sympathetic and parasympathetic nervous systems are two divisions of autonomic nervous system and these are antagonistic (opposite to each other) in their functions.

UP Board Notes for Class 10 Science Chapter 8 The Circulatory System

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The Circulatory System Learning Objectives

After completing this chapter, you will be able to:

  • Describe the composition, physical characteristics and functions of blood; describe the ABO blood groups and the Rh factor;
  • Describe the structure and functions of the heart;
  • Trace the pathway of blood circulation through the heart;
  • Name the major blood vessels entering and leaving the heart;
  • Describe the cardiac cycle and heart sounds;
  • Differentiate between arteries, veins and capillaries;
  • Differentiate between systemic and pulmonary circulations;
  • Describe the structure and distribution of lymphatic vessels and their functions;
  • Differentiate between blood and lymph.

The Circulatory System Circulation of Fluids in Humans

  • In human beings, a rapid supply of nutrients, oxygen and hormones to various tissues and the immediate disposal of waste products are essential requirements. So, our body has a specialized circulatory system. The circulatory system has three main parts.
  1. Circulatory medium – Blood, tissue fluid and lymph
  2.  Blood vessels – Arteries, veins and capillaries
  3.  Pumping organ – Heart The circulatory system, in different animals, are of two types – open and closed. The differences between the two are given in Table.

The-circulatory-system-Differences-between-closed-circulatory-system-and-open-circulatory-system

Circulatory Medium – Blood, Tissue Fluid and Lymph

Our body has three different types of fluids:

  1. Blood- Found in the heart and blood vessels (arteries, veins and capillaries)
  2. Tissue fluid – Found in the intercellular spaces
  3. Lymph-Found in the lymph vessels and lymphatic organs (e.g. spleen and tonsils)

Blood – Composition and Functions

  • An average human being has about 5.5 litres of blood in his body. About 50-60 per cent of the blood is a fluid called plasma and the remaining 40-50 per cent is made of cellular elements called corpuscles that are held in suspension. Blood always flows from the heart through the arteries and back to the heart through the veins.

Physical properties of the blood

  • Blood is a red-coloured, viscous and complex tissue fluid. It is salty in taste and slightly alkaline with a pH range of 7.35-7.45. Blood constitutes about 6 to 8 per cent of the total body weight.

Composition of blood

  • Blood is made up of two main components – plasma (fluid part) and cellular or formed elements (blood corpuscles, solid part).

The circulatory system Composition of blood

Plasma – the fluid part

  • Plasma is a straw-coloured aqueous part of the blood in which formed elements remain suspended. It forms about 50-60 per cent of the blood volume. Plasma contains water (about 90-92 per cent), inorganic salts (about 1-2 per cent) and organic compounds (about 7-8 per cent).
  1. Plasma = Blood – Formed elements
  2. Plasma from which the protein fibrinogen has been removed is called serum.
  3. Serum Plasma – Fibrinogen

Cellular elements

  • In human beings, three types of cellular elements are found suspended in the plasma.
  • Red blood corpuscles (RBCs) or erythrocytes
  • White blood corpuscles (WBCs) or leucocytes
  • Platelets or thrombocytes

The process by which new blood cells are formed is called haemopoiesis or haematopoiesis.

The circulatory system Three types of cellular elements suspended in the plasma

The circulatory system Centers of blood cell production

Red Blood Corpuscles (RBCs)

  • Red blood corpuscles or erythrocytes (Gk. erythrose: red) are biconcave and enucleated (i.e. without a nucleus), disc-like cells which are flat in the centre, and thick and rounded at the periphery. Young RBCs have a nucleus, but as they mature, the nucleus degenerates. Such a shape is of great advantage to RBCs as it increases their surface area.
  • Due to the lack of organelles (such as mitochondria and endoplasmic reticulum), their oxygen demand is negligible.
  • The RBCs are very small in size. This small size helps them in absorbing oxygen and enables them to move in very fine blood capillaries throughout the body of a person.
  • RBCs are produced in the bone marrow of long bones, ribs, vertebrae and skull bones. The average life span of erythrocytes is about 120 days.
  • Their average number ranges from 5 million to 5.5 million in human males and 4.5 million to 5 million in human females.The circulatory system Erythrocytes

Haemoglobin (Hb)

  • The RBCs have a colourless spongy body which contains haemoglobin. The haemoglobin is the respiratory pigment which is composed of an iron-containing part known as haeme and a protein part known as globin.
    The oxygen after diffusing into blood capillaries combines with the iron-containing part of RBCs and forms oxyhaemoglobin.
  • Absence of a nucleus and other organelles makes RBCs more efficient

1.  RBCs in mammals are enucleated when mature, that is, they lack a cell nucleus. This is attributed to their oxygen-carrying capacity. These cells become more efficient in their work because of the following reasons:

  •  More space is available for haemoglobin which carries oxygen.
  • The shape changes to a biconcave disc rather than a normal sphere, increasing the surface area volume ratio for a better exchange of oxygen and carbon dioxide.
  • The biconcave shape optimises the flow of the blood within blood vessels as these cells move in a laminar flow, i.e. in parallel rows without any swirls.
  • No nucleus means no DNA, so proteins cannot be synthesized. Their inability to carry out protein synthesis means they cannot be attacked by many viruses.

2. RBCs in mammals do not have mitochondria which is the site of cellular respiration. This ensures that all of the oxygen taken up by these cells from the lungs is delivered to the target tissue and not utilised by the cell itself.

3. RBCs also lack organelles like the Golgi apparatus and endoplasmic reticulum. This decreases their size markedly from 24 u to 7-9 μ and makes them small enough to pass through the smallest capillaries.

White Blood Corpuscles (WBCs)

The circulatory system Differences between closed circulatory system-and-open-circulatory-system

  • White blood corpuscles or leucocytes (Gk. Leucos: white) are rounded or Fig. irregular-shaped cells. They are capable of amoeboid movement. They are colourless since they lack haemoglobin.
  • They are produced in the bone marrow. Leucocytes are of two types – 
  • granulocytes (contain granules in their cytoplasm and have lobed nuclei) and
  • agranulocytes (lack granules in their cytoplasm and have unlobed nuclei).

1. Granulocytes
Granulocytes are spherical in shape and larger than the red blood cells. They have lobed nuclei and their cytoplasm contains granules. There are three types of granulocytes – (a) neutrophils, (b) basophils and (c) eosinophils.

  • Neutrophils: Neutrophils account for 50-70% of the WBCs in our blood. Their cytoplasm contains very fine granules. The nucleus has 3-6 lobes. The granules stain with both acidic and basic. Dyes. Neutrophils are highly phagocytic in nature. Neutrophils contain special proteins called defensins, which have an antimicrobial activity against germs.
  • Basophils: Basophils account for only 0.5% of the total WBCs. They are of the same size or slightly smaller than neutrophils. The nucleus is indistinctly lobed. The cytoplasmic granules stain with basic dyes. Basophils produce histamine and heparin, which intensify the inflammatory response in an allergic reaction. During inflammation, the blood vessels dilate making their walls leaky for leucocytes to squeeze out of the blood capillaries and engulf the germs. This process is known as diapedesis.

The-circulatory-system-Inflammatory-response

 

  • Eosinophils: Eosinophils account for 1-4% of the total WBCs. The nucleus is two-lobed. The cytoplasmic granules are large and rough and stain dark red with acidic dyes (e.g. eosin). They phagocytose the antigen-antibody complex. They release chemicals to combat inflammation during an allergy.

2. Agranulocytes
Agranulocytes’ nucleus is single and typically spherical or kidney-shaped. The cytoplasm does not contain granules. There are two types of agranulocytes – (a) lymphocytes and (b) monocytes.

  • Lymphocytes: Lymphocytes account for about 25% of the total WBCs. The nucleus is large, and spherical, with a dent-like depression on one side, which occupies most of the cell volume. They produce antibodies and play a crucial role in immunity.
  • Monocytes: Monocytes are the largest leucocytes and account for 3-8% of the total WBCs. The nucleus is large and U- or kidney-shaped. They arephagocytic in nature and ingest germs and clean up damaged cells. Hence, monocytes are referred to as wandering macrophages.

The-circulatory-system-Type-of-white-blood-cells

Functions of WBCs

  • WBCs help in destroying solid substances and germs, especially bacteria, by engulfing them. This defensive process of fighting against disease-causing germs is termed as phagocytosis. Neutrophils are most active in this role. By doing so they protect the body from diseases, i.e. they are responsible for

immunity.

  • They also help in the formation of antibodies which neutralize or kill the germs that enter our body.

Inflammation

  • It is a defensive response of the body to tissue damage by microbes, physical agents or chemical agents. It is characterised by four fundamental symptoms – redness, pain, heat and swelling.
  • The following reasons of inflammation are given below:
  • Vasodilation, i.e. increase in diameter of surrounding blood vessels.
  • Increased permeability of blood vessels. It allows defensive substances in blood to enter the injured area and phagocytosis occurs.
    Thus, it is to be clearly understood here that inflammation is not a role of WBCs but phagocytosis at the point of inflammation is carried out by neutrophils and monocytes. In case of an allergic reaction, basophils intensify the inflammatory response.

Pyogenesis

  • (pyo = pus; genesis = to produce)
  • The phenomenon of pus production during an inflammation is pyogenesis. Pus is a thick whitish fluid which contains living and dead WBCs and dead tissue debris.

Blood platelets (Thrombocytes)

  • Blood platelets are colourless, oval or round (plate-like in active form), cytoplasmic fragments formed from giant cells of the bone marrow. These are found floating in the blood. These are enucleated (without a nucleus), bound by a membrane and contain a few organelles. Their life span is about 5-10 days. Thrombocytes help in blood clotting. They release a chemical, thromboplastin that initiates the process of clotting of blood. They can repair slightly damaged blood vessels.

The-circulatory-system-Platelets

Let us understand…

  • An antigen is a protein produced by the body in response to the presence of an antigen and combines specifically to that antigen. WBCS act as antibodies by phagocytosing the antigen.
  • Toxin is a poisonous substance produced by an antigen (foreign body) which has unfavourable effects on the body of the organism. In other words, a toxin is toxic the Infected organism.
  • Toxoid is an activated or weakened toxin produced by an antigen which is not toxic anymore. However, it is still capable of acting as an antigen and hence, is used as a vaccine which stimulates production of specific antibodies in the blood of an organism.
  • Antibody neutralizes a specific antigen.

Blood diseases

  • An increase in the number of RBCs much more than normal is called polycythemia.
  • A decrease in the RBC count is called erythrocytopenia.
  • An enormous increase in WBCs at the cost of RBCs causes leukaemia – the blood cancer.
  • A decrease in the WBC count is known as leucopenia.

Functions of blood

Blood is a complex fluid which performs a number of roles in our body. It transports, regulates and protects.

1. Transportation

  • Transport of nutrients: The digested food substances are absorbed by the blood at the site of absorption (small intestine) and transported to different organs of the body.
  • Transport of respiratory gases: Blood transports oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the respiratory surface, i.e. lungs.
  • Transport of waste products: The metabolic waste substances produced in the body are transported by the blood to the excretory organs.
  • Transport of body secretions: Blood transports chemical secretions like hormones, from the site of their secretion (endocrine glands) to the target organs.

2. Regulation

  • Regulation of body temperature: Blood helps to control the body temperature by evenly distributing the heat produced in one part of the body to different parts.
  • Maintenance of pH: The plasma proteins are amphoteric in nature, i.e. they act as a buffer and thus maintain the pH of blood.
  • Water balance: Blood maintains water balance to a constant level by bringing about constant exchange of water between the circulating blood and the tissue fluid.

3. Protection

  • Clotting of blood protects against blood loss: Prothrombin and fibrinogen proteins of plasma help in blood clotting at the site of injury. This prevents blood loss.
  • Defence against infection: Blood contains WBCs that are phagocytic in nature. WBCs also produce antibodies that destroy the bacteria, after neutralizing their toxins, and thus, play a protective role.

The Circulatory System Clotting of Blood

  • Blood is in a fluid state when inside the blood vessels. Blood does not clot in uninjured vessels due to the presence of natural anticoagulants called heparin and antithrombin, produced in the liver. Blood usually clots after it escapes from the blood vessels.
  • When blood vessels get damaged due to any external injury or an internal cause, three basic mechanisms become operational in the following sequence:

Step 1. Vascular spasm occurs. When a blood vessel (artery or vein) other than a capillary is injured, the smooth muscles in its wall contract to reduce blood loss.

Step 2. Platelet plug formation occurs. The platelets get activated on coming in contact with the damaged blood vessel. Platelets undergo drastic changes in their shape and release several substances involved in the step of blood coagulation. The activated platelets become sticky and form a platelet plug at the damaged spot. This plug is initially loose and is tightened by the fibrin threads formed in the next step.

Step 3. Coagulation of blood occurs. The process of clotting of blood is known as coagulation. A clot is a network of insoluble protein fibres called fibrin in which the cellular components of the blood get trapped. Coagulation is a complex process in which several coagulation factors (I to XIII) come into action in a definite sequence. It can be divided into three basic stages as follows:

Stage 1. Formation of prothrombin activator: A protein called Tissue Factor (TF) or thromboplastin found on the surface of various body cells such as brain, lungs and intestines initiates the formation of prothrombin activator. It is a cascade of events which ends with the activation of the enzyme thrombokinase also called factor X or Stuart factor which in the presence of Ca++ ions forms a prothrombin activator. The Stuart factor is not released by platelet disintegration. However, bursting of platelets provides phospholipids that activate this factor.

Stage 2. Conversion of prothrombin to thrombin: The prothrombin activator formed in stage 1 now converts prothrombin to thrombin with the help of Ca++ ions.

Stage 3. Conversion of fibrinogen to fibrin: Fibrinogen is a soluble protein found in the plasma. Thrombin formed in stage 2 now converts soluble fibrinogen to insoluble fibrin in the presence of Catt ions.
The platelet plug is strengthened by fibrin which forms a network at the site of the injury. Thrombin also causes more platelets to adhere to each other thus strengthening the clot.

Clot Vs Thrombus

  • Intravascular clot formed in an unbroken blood vessel is called a thrombus. Every clot is not a thrombus.

The-circulatory-system-Mechanism-of-clotting-of-blood

Blood Groups and Blood Transfusion

Blood groups

  • In 1901, Karl Landsteiner, a German biochemist, proposed that the blood of different individuals has some biochemical differences. There are two types of proteins in the human blood.
  1. Agglutinogen or antigen is present on the surface of RBCs. It is called the corpuscle factor.
  2. Agglutinin or antibody is a protein present in the blood plasma and is called the plasma factor. There are two kinds of antigens, A and B, and two kinds of antibodies, a and b, in the blood. Antigen A and antibody a are antagonistic or incompatible and cause self-clumping. Similarly, antigen B and antibody b are incompatible and cause self-clumping. Antigen A is compatible with antibody b and antigen B is compatible with antibody a.
  • On the basis of the type of antigen present on the surface of RBCs as given below, a system of blood groups known as ABO system, in which there are four blood groups, is recognized in the human blood.
  • Group A with antigen A and antibody b.
  • Group B with antigen B and antibody a.
  • Group AB with both A and B antigens but no antibodies.

The-circulatory-system-Human-blood-groups-and-their-compatibility

  • Group O has no antigen but both antibodies a and b.

Blood transfusion

  • Blood transfusion is a procedure of transfer of blood or blood components from one person (donor) into the bloodstream of another person (recipient). The antigens of the donor’s blood can react with antibodies of the recipient’s blood and cause clumping of RBCs. Thus, antigen A present in the RBCs of blood group A individuals reacts with antibodies of plasma of blood group B individuals and vice versa. This phenomenon is known as agglutination. Agglutination may cause serious consequences and even prove fatal.
  • The RBCs of blood group O individuals lack antigens and are not clumped by antibodies present in the serum of the recipient’s blood. It means blood group O can be given to persons with blood group O, A, B or AB. Hence, persons with blood group O are called universal donors.
  • However, persons with blood group AB lack antibodies in their plasma, so they can receive blood from A, B, O or AB blood groups. Such persons are called universal recipients.

Rh factor (Rhesus antigens)

  • Landsteiner and Wiener discovered in 1940 that the surface of human RBCs contains a protein that is also found in the RBCs of Rhesus monkeys. So, it was termed an Rh antigen or Rh factor. Those persons who have this factor are called Rh-positive and others as Rh-negative.
  • Both Rh-positive and Rh-negative persons are quite normal. The problem arises when Rh- blood comes in contact with Rh+ blood either due to blood transfusion or during pregnancy.

Incompatibility During Blood Transfusion

  • The Rh-blood can be given safely to an Rh+ individual. When Rh* blood is transfused into an Rh- person, the recipient forms antibodies in her/his blood. However, no complications develop after the first transfusion.
  • In case of a second transfusion of Rh* blood to an Rh person, the recipient’s anti-Rh factors attack and destroy the donor’s red blood corpuscles. Therefore, it is always advised that the patient’s Rh factor is determined before transfusion.

Incompatibility during pregnancy

  • A serious problem arises if an Rh™ mother is carrying an Rh foetus. The Rh blood of the foetus will stimulate the formation of anti-Rh factors or antibodies in the mother’s blood. During the first pregnancy, enough antibodies are not produced to harm the foetus.
  • During the second pregnancy, if the foetus is Rh*, more antibodies will be produced in mother’s blood. Due to the cumulative effect of antibodies produced the second time, in addition to the antibodies already present in mother’s blood, a large number of RBCs of the foetus are destroyed. This causes death of the foetus. This called erythroblastosis fetalis.

Parts of Human Circulatory System

Blood vessels 1

  • The blood vessels are a system of channels through which the blood flows. There are three kinds of blood vessels – arteries, veins and capillaries.

1. Arteries are the blood vessels that carry blood away from the heart to the various parts of the body.

  • All arteries (except the pulmonary artery) carry oxygenated blood.
  • An artery has thick and elastic muscular walls.
  • Arteries have a small lumen without valves.
  • The blood flows in spurts in arteries corresponding with contractions of the ventricles in the heart.

2. Capillaries are microscopic, thin vessels that carry blood from arterioles to small their venules.

  • They are found abundant in those tissues or organs where the rate of metabolism is very fast.
  • Capillaries are made of single-layered endothelial tissue with a very narrow lumen.

The-circulatory-system-Capillaries-connect-arteries-and-veins

  • Their wall is very thin, having a tunica intima Capillaries connect arteries and veins.
  • Their wall is very thin, having a tunica intima(also called tunica interna) layer only. They have a large lumen with valves.

Their walls are thin to facilitate the exchange of food material, gases and waste between the blood and the tissues.

Functions of capillaries

  • To allow inward and outward diffusion of glucose, amino acids, urea, etc.
  • To allow diffusion of oxygen into intercellular fluids and inward diffusion of carbon dioxide from intercellular fluids.
  • To allow movement of leucocytes through capillary walls. (RBCs and proteins do not move out of the capillary walls)The-circulatory-system-Differences-between-arteries-and-veins
  • Diagrammatic relationship between arteries, veins and capillaries

3. Veins are the blood vessels that carry blood from the body parts to the heart.

  • All veins (except the pulmonary vein) carry deoxygenated blood.
  • The wall of a vein is thinner as compared to the arterial wall.
  • They have a wider lumen.
  • Blood flows uniformly within veins.
  • Veins have semilunar valves that prevent the backward flow of blood. These valves are formed from folds of the inner walls of the veins. Forward pressure of the blood forces the valve to open and the blood flows towards the heart, whereas the backflow of the blood causes the valve to close.The-circulatory-system-Action-of-a-semilunar-valve-in-a-vein
  • Action of a semilunar valve in a vein
  • Differences between an artery and a vein are given have the power to constrict or dilate as their wall lacks in Table.

The-circulatory-system-Differences-between-arteries-and-veins

Vasodilation and Vasoconstriction

  • The smooth muscle layer of arteries and veins (called the tunica media) has a nervous supply with it. When these nerves are stimulated, the smooth muscles contract, and squeeze
  • the wall of the vessel leading to a narrow lumen. Such a decrease in the lumen size is called vasoconstriction.
  • When the stimulation is removed, the muscle fibres relax and the lumen size increases leading to vasodilation.
  • This clearly indicates the role played by the smooth muscle fibres in the walls of arteries and veins in these
    phenomena. It is to note here, that capillaries do not muscle fibre layer.
  • When we walk in the hot sun, our face turns pink due to vasodilation of the blood vessels supplying blood to the skin capillaries. There is an increase in the flow of blood into the capillaries on the surface of the skin. On the contrary, the skin turns pale due to vasoconstriction when it is too cold.

The Human Heart

Position, shape and size of the heart

  • The human heart is located between the lungs in the thoracic cavity, with its lower end inclined towards the left. The heart is a hollow, fibromuscular organ and is somewhat conical in shape. It is about the size of one’s fist. It’s pointed end projects to the left.
  • The heart is enclosed by a double-layered membranous sac called the pericardium. It protects the heart from mechanical injury. The space between two pericardial membranes is the pericardial space, which is filled with the pericardial fluid. The pericardial fluid keeps the heart moist and reduces friction between the heart wall membranes. The human heart is made of cardíac muscles or myocardia which contract rhythmically by self-generated impulses.

External structure of the heart

  • The human heart is a four-chambered organ divided by septa into two halves – the right half and the left half. Each half consists of two chambers – the upper, small-sized auricle or atrium and a lower, large-sized ventricle.

The-circulatory-system-Differences-between-closed-circulatory-system-and-open-circulatory-system

 

Internal structure of the heart

  • Internally, the heart has the following main components – four chambers (two auricles and two ventricles), great blood vessels that carry blood to the heart and away from it, and various apertures and valves.

Chambers of the heart

  1. Auricles – The receiving chambers: The auricles or atria are thin-walled chambers and are separated from each other by an inter-auricular septum.
  2. Ventricles – The discharging chambers: The ventricles are thick-walled chambers and are separated from each other by an obliquely placed inter-ventricular septum. The wall of the left ventricle is the thickest because it has to pump blood into vessels, which in turn carry the blood to long distances up to the head, trunk and extremities. The right ventricle pumps blood to the pulmonary arteries, which carry it to the lungs. The walls of the atria are thinner than that of ventricles because they just have to deliver blood into the ventricles.

Great blood vessels of the heart
the blood vessels that enter or leave the heart are called great blood vessels.

Blood vessels entering the heart

1. The right auricle receives blood from three blood vessels.

  • Superior (Anterior) vena cava or Perceval brings deoxygenated blood from the head and upper region of the body.
  • Inferior (Posterior) vena cava or postcaval brings deoxygenated blood from the lower region of the body.
  • Coronary sinus brings deoxygenated blood from the heart’s wall itself into the right auricle.

2. The left auricle receives four blood vessels.

  • Pulmonary veins – The left auricle receives blood from two pairs of pulmonary veins, one pair from each lung. These bring oxygenated blood from the lungs.

Blood vessels leaving the heart

  • Pulmonary artery arises from the right ventricleand carries deoxygenated blood to the lungs for oxygenation.The-circulatory-system-The-location-and-functions-of-major-blood-vessels-of-human-cardiovascular-system
  •  Systemic aorta originates from the left ventricle and supplies oxygenated blood to all body parts, except the lungs.
  • Coronary arteries arise from the base of the aorta. These supply blood to the heart muscles. If coronary arteries get blocked, then it can cause heart attack.

shows the location and functions of major blood vessels of human cardiovascular system.

Apertures and valves in the heart

  • There are four valves in the heart which control the flow of blood within the heart and its passage to various parts of the body through the great blood vessels.
  1. The bicuspid valve (also called the mitral valve or left auriculo-ventricular valve) guards the opening of the left auricle into the left ventricle. This valve consists of two flaps or cusps.
  2. The tricuspid valve (also called the right auriculo- ventricular valve) guards the opening of the right auricle into the right ventricle.
    Both, the bicuspid and the tricuspid valves allow blood to pass from auricles to the ventricles and prevent the backflow of blood.
  3. Semilunar or pulmonary valves are present at the base of the pulmonary artery. These valves allow the flow of blood from the right ventricle to the pulmonary artery and check the backflow of blood into the ventricles.
  4. Aortic semilunar valve is present at the point of origin of the aorta. In all, there are three semilunar valves in the vessels. They allow blood to pass from left ventricle to the aorta and check the return of blood into the ventricles.

Double Circulation

  • The circulation of blood in the human heart is called double circulation because the blood enters and leaves the heart twice in each heartbeat. Circulation of blood between the heart and body organs (except lungs) is called systemic circulation. Circulation of blood between the heart and the lungs is called pulmonary circulation.

Systemic circulation

  • The left ventricle pumps the oxygenated blood into the systemic aorta. Aorta gives off branches to all the organs of the body except lungs.
  • From these arteries, oxygen is diffused into the tissues. Deoxygenated blood from visceral organs is brought to the right auricle by superior and inferior venae cavae. This part of circulation from the left ventricle to the right auricle of the heart via body tissues (except lungs) is called systemic circulation. 

Pulmonary circulation

  • The circulation of blood from the right ventricle to the left auricle of the heart via lungs is called pulmonary circulation. The right ventricle pumps deoxygenated blood to the lungs for oxygenation. Oxygenated blood from the lungs is returned to the left auricle by four pulmonary veins.

The-circulatory-system-Double-circulation-in-human-heart

The-circulatory-system-Circulation-of-blood-to-various-parts-of-the-body

Cardiac Cycle – Systole and Diastole

  • The sequence of events, that take place during the completion of one heartbeat, is known as the cardiac cycle. It involves repeated contraction and relaxation of the heart muscles. A contraction is termed as systole and a relaxation is termed as diastole.
  • One complete heartbeat or cardiac cycle consists of systole and diastole both atria and both ventricles followed by a short pause. It lasts for about 0.8 seconds.
  • The events that take place during the completion of one heartbeat are -the auricular systole, the ventricular systole and the joint diastole or complete cardiac diastole. 

1. Auricular systole: The two auricles act as a pump to force the venous blood into the ventricles. The ventricles are in diastole at this time. During auricular systole, the auricular muscles contract. and the openings of venae cavae and pulmonary vein close. The tricuspid valve and bicuspid valve

The-circulatory-system-a.-Blood-flow-during-cardiac-cycle-b.-Two-main-phases-of-heart-beat

  • open and the blood enters the ventricles through these valves. At the end of an atrial systole, as the two auricles relax, more venous blood is passed from the great veins into the atria to fill them up.

2. Ventricular systole: With the onset of atrial diastole the ventricles start contracting. The bicuspid and tricuspid valves (also known as atrioventricular or AV valves) close to prevent the backward flow of blood from ventricles to the atria. When the pressure in the ventricles increases, semilunar valves open and blood is passed into the great arteries.

3. Joint diastole: At the end of a ventricular systole, the ventricles relax. Also at this stage, the atria are still in their diastole. Since all the heart chambers are in diastole, this stage is called joint diastole. During this phase, blood continues to flow into the auricles from the great veins. As the atria fill with blood, the pressure in them rises and becomes greater than that in the relaxed ventricles. Blood then flows from the auricles to respective ventricles through the AV valves.

How is cardiac cycle conducted?

  • The heart is supplied by a network of nerves but these are not responsible for the initiation of the cardiac cycle.
  • The heart can keep on contracting and relaxing without any stimulation from these nerves. However, the heart.
  • has a regulating system of its own called the conduction system. It is a system of specialised muscle tissue which initiates and spreads the electrical impulses to stimulate a cardiac cycle.

It has the following parts:

  • SA node or sinoatrial node: It is located in the wall of the right atrium near the opening of the superior vena cava. As it initiates each cardiac cycle and sets the pace or rhythm for the heart beat rate, it is called the pacemaker of the heart.
  • AV node or atrioventricular node: It is located near the inferior part of the interauricular septum. The impulses initiated by the SA node make the atria contract and the electrical signals are received by the AV node.
  • AV bundle or atrioventricular bundle: It is a tract of conducting fibres that arise from the AV node and run along the interventricular septum. The impulse travels through these fibres, also called the “Bundle of His”.
  • Purkinje fibres: These fibres emerge from the Bundle of His as branches and spread into the myocardium of ventricles. These fibres stimulate the contraction of ventricles, hence called conduction myofibers.

Electrocardiogram (ECG)

  • The muscle cells or fibres of the heart are specialised at certain parts of the heart to generate electric currents that cause a normal rhythmic heartbeat.

The-circulatory-system-Electrocardiogram-(ECG)

  •  A recording of the electrical events that control the cardiac cycle is called an electrocardiogram (ECG). The instrument used to record the changes is an electrocardiograph.
    The ECG is a useful diagnostic tool for heart diseases like tachycardia (a high pulse rate above 100/minute), bradycardia (a slow pulse rate below 60/minute), ventricular fibrillation and heart block.

Pulse rate

  • The rhythmic contraction of the heart can be felt as a jerk in certain arteries which are superficial in position. This is the arterial pulse. Each ventricular systole starts a new pulse. It proceeds as a wave of expansion throughout the arteries and disappears in the capillaries. The pulse rate is the same as the heartbeat rate. The pulse rate in a normal adult man is about 64-72 beats per minute while in a woman 72-80 beats per minute. The pulse rate in infants is about 140 beats per minute.

Heart sounds – Lubb and dubb

  • The various valves present at the outlet and inlet of ventricles determine the direction of flow of blood in the heart. The opening and closing of these valves cause heart sounds. These sounds can be heard by using a stethoscope (an instrument that magnifies sounds and conducts them to the ear). These sounds are heard as ‘lubb’ and ‘dubb’ sounds.
  • The lubb sound (first heart sound): This sound is caused by the vibrations initiated by the closure of tricuspid and bicuspid valves accompanied by the contraction of ventricular muscles at the start of ventricular systole. It is also called a systolic sound. Lubb sound is low-pitched, not very loud and is of a long duration.
  • The dubb sound (second heart sound): This sound is caused by the closure of the semilunar valves and marks the end of ventricular systole and beginning of ventricular diastole. The dubb sound is high-pitched, louder and shorter in duration.

An abnormal heart sound is called a murmur. This is caused problems with the valves.

The-circulatory-system-Measuring-of-blood-pressure

Blood pressure

  • It is the force with which blood pushes against the walls of the arteries. It is generally measured in terms of how high it can push a column of mercury. When the ventricles contract, the pressure of blood inside the arteries is highest and this pressure is termed as systolic blood pressure.
  • In a healthy young human being, it is about 120 millimetres of mercury (120 mm Hg). When ventricles relax, the pressure of blood inside the arteries is comparatively less and this pressure is termed as diastolic pressure. It is about 80 millimetres of mercury (80 mm Hg) in a healthy young man. Thus, a healthy young man is said to have a normal blood pressure of 120/80 mm of Hg. The instrument used to measure blood pressure is called a sphygmomanometer.
  • Blood pressure =systolic/diastolic = 120/80mm of Hg

Portal System

  • A vein that does not carry deoxygenated blood directly to the heart but forms a network of capillaries on another organ before reaching the heart is called a portal vein. It begins and ends in capillaries. The components of the portal vein constitute the portal system. In human beings, two main portal systems – the hepatic and the hypophyseal portal systems are present.

Hepatic Portal System

  • The venous blood from gastrointestinal organs and spleen is drained into the liver before returning to the heart. Veins from various regions of the gastrointestinal tract and spleen unite to form the hepatic portal vein. It divides into two branches, right and left, which enter into the corresponding liver lobes and break up into capillaries to supply blood. A pair of hepatic veins carry this deoxygenated blood from the liver to the inferior vena cava.

Why is there a need for the hepatic portal system?

  • The blood in hepatic portal vein is rich in nutrients absorbed from the digestive tract. The liver absorbs substances like glucose and stores it as glycogen for use when required. It also modifies other substances so that they can be used by cells. It detoxifies harmful substances in the blood. It also destroys bacteria by phagocytosis.

The-circulatory-system-Arteries-and-veins-associated-with-liver-and-kidney

Lymphatic System

  • The lymphatic system comprises a colourless fluid called lymph and a network of fine channels namely, lymphatic capillaries (lacteals) and vessels (ducts), and the lymph nodes.

The-circulatory-system-Lymphatic-system

Lymph

  • Lymph is a colourless fluid. It is a part of the tissue fluid which in turn is a part of blood plasma. So, the composition of tissue fluid and lymph is the same as that of blood plasma but tissue fluid and lymph have lower protein contents.

The-circulatory-system-Differences-between-blood-and-lymph

  • Lymph consists of a fluid matrix in which the white blood corpuscles or leucocytes are present. Unlike blood, lymph does not have red blood corpuscles, platelets and plasma proteins.

The Circulatory System Functions of The Lymph

The lymph performs many functions.

  • It carries carbon dioxide and nitrogenous waste materials that diffuse into the blood through the tissue fluid.
  • It carries lymphocytes and antibodies from the lymph nodes to the blood.
  • It transports fats (fatty acids and glycerol) from the intestine to the blood.
  • It destroys microorganisms and foreign particles in the lymph nodes.
  • It drains excess tissue fluid from the intercellular spaces back into the blood.
  • It carries the plasma protein macromolecules, synthesized in the and horn endocrine glands to the blood.

Lymph vessels or lymphatics

  • The lymph capillaries join to form the lymphatic vessels. These lymph vessels are like capillaries but have comparatively thin walls and numerous valves. The smaller lymphatic vessels unite to form larger vessels and they unite to form two main lymphatic ducts.
  • The lymph vessels at the right side of the head, neck and the right arm enter into a large vessel, the right lymphatic duct which opens into the right subclavian vein.

Lymph nodes

  • At specific points in the lymph vessels, there are enlargements like beads of a string. These are called lymph nodes. Lymph nodes contain lymphocytes, plasma cells and macrophages. The lymph is filtered through the lymph nodes. The macrophages remove microorganisms and foreign particles from the lymph. The lymphatic nodes also add lymphocytes and antibodies to the lymph from where these are carried to the blood.
  • Lymph nodes are abundant in the regions of neck, armpit and groin.
  • Tonsils and adenoids are masses of lymphatic tissues.

The thymus and spleen are important lymphatic organs of the body.

Tonsils

  • Tonsils are aggregations of lymphatic nodules enclosed by brane. These are located in a ring at the junction of oral cavity and pharynx.

Functions of tonsils

  • Their location is best suited to protect the body against entry of any foreign substance through the oral cavity.
  • They also produce lymphocytes and antibodies.

Spleen

  • Spleen is the largest mass of lymphatic tissue found in our body. It measures about 12 cm in length and is located in the region between the fundus of stomach and diaphragm. It is covered by the peritoneal membrane.The tissue of spleen is of two types:
  1. White pulp – The lymphatic tissue
  2. Red pulp – Sinuses filled with venous blood and tissue cords consisting of macrophages, lymphocytes and granulocytes.

Functions of spleen

  • It produces antibodies, phagocytic cells and destroys dead RBCs and platelets.
  • In embryonic stage, it produces RBCs.
  • It also acts as a reservoir of blood which is released during emergencies such as haemorrhage.

The Circulatory System Summary

  • The flow of extracellular fluid in the body is called circulation and the organs concerned with this transport form the circulatory system.
  • Human beings have an efficient circulatory system. It consists of:
  • A circulatory medium – blood
  • A system of blood vessels – arteries, veins and capillaries
  • A pumping organ heart.
  • Blood is made up of plasma and cellular elements. The cellular elements include RBCs, WBCs and platelets.
  • Blood does not clot in uninjured vessels due to the presence of a strong, natural anticoagulant called heparin or antithrombin, produced by the liver.
  • The glycoprotein or corpuscle factor present on the surface of RBCs and a protein or the plasma factor present in the blood plasma determine the type of blood group of a person. Blood groups in humans are of four types (A, B, AB, O) in ABO grouping system.
  • Blood of group O can be given to any blood group, hence people with blood group O are called universal donors.
  • Persons with blood group AB can receive blood from all blood groups, hence, are called universal recipients.
  • All arteries carry oxygenated blood, except pulmonary arteries, which carry deoxygenated blood from the heart to the lungs for oxygenation.
  • All veins carry deoxygenated blood except pulmonary veins, which carry oxygenated blood from the lungs to the heart.
  • The human heart is a fibromuscular organ somewhat conical in shape. It is about the size of a fist. Its weight is about 300 g in an adult human being.
  • The human heart is protected by a double-walled membranous sac called pericardium.
  • The human heart is a four-chambered structure, divided by septa Into two halves the right and the left. Each half consists of an upper, small-sized, thin-walled chamber called auricle and a lower, large- sized and thick-walled ventricle.
  • The left auriculo-ventricular aperture is guarded by the bicuspid valve, which consists of two flaps or cusps, and the right auriculo-ventricular aperture is guarded by the tricuspid valve made up of three flaps or cusps. These valves allow blood to pass from auricles to ventricles and also prevent the backward flow of the
    blood.
  • Circulation of blood in the human heart is called double circulation because blood enters and leaves the heart twice. Circulation between the heart and the body organs except lungs is called systemic circulation. Circulation between the heart and the lungs is called pulmonary circulation.
  • The sequence of events that take place during the completion of one heartbeat is known as cardiac cycle. It lasts for about 0.8 seconds.
  • The rhythmic contraction of heart is felt as a jerk in certain arteries that are superficial in position. This is the arterial pulse. The pulse rate of a person is the same as the heartbeat rate.
  • Blood pressure is the force with which blood pushes against the walls of arteries. The blood pressure of a healthy person is 120/80 mm Hg. The instrument used to measure blood pressure is called sphygmomanometer.
  • The lymphatic system comprises of -lymph, lymphatic capillaries and vessels, and lymph nodes.

 

UP Board Notes for Class 10 Science Notes Chapter 7 Control and Coordination

by

Chemical Coordination in Plants

Learning objectives

After completing this chapter, you will be able to:

  • Recognize the need for chemical coordination in plants;
  • Describe various tropic movements in plants.
  • Discuss the role of plant growth regulators;
  • List the major plant hormones and discuss their
    Physiological effects in regulating plant growth:
    • auxins
    • gibberellins
    • cytokinins
    •abscisic acid
    • ethylene

The activities that occur inside our body require proper coordination between the organs. Like animals, plants also need internal coordination for their growth and development. Plants do not have a nervous system, like animals, but they still respond to internal and external changes in the environment around them. Plants can detect changes in light, water, touch, chemicals, and gravity and respond to these changes by the action of hormones. Since plants do not have a nervous system, they use hormones for coordination and response. Therefore, the function of control and coordination in plants is performed by chemical substances called hormones or plant growth regulators.
In this chapter, we shall learn about chemical coordination in plants and how it is brought about.

Chemical Coordination in Plants Stimuli and receptors

If we accidentally touch any hot object, we immediately withdraw our hands. Thus, we respond to changes in our surroundings. Any change in the environment to which an organism responds and reacts is called a stimulus (plural: stimuli). For example, the leaves of touch-me-not plants fold if we touch (stimulus) them.

Chemical Coordination in plants Touch-me-not plant

Touch-me-not plant (Mimosa pudica)

Stimuli are detected by a group of cells called receptors. For example, our skin, eyes, ears, nose and tongue contain different receptors.
Plants and animals respond to stimuli in a different ways. Animals respond to stimuli in many ways because they have a nervous system. However, plants react to stimuli in a very limited way because they do not have a nervous system. Thus, response to stimuli is a characteristic property of each living organism.
Plant movements in response to stimuli can be of two types:

  • Tropic movements
  • Nastic movements

Chemical Coordination in Plants Tropic movements or tropism

The environment has a great influence on a plant’s shape. A growth response that results in the movement of plant parts towards or away from stimuli is called tropism. In simpler terms, the movement of a plant in the direction of a stimulus is known as tropism. It is of two types-positive tropism and negative tropism.

  • When the growing movement of the plant part is towards the stimulus, it is called positive tropism.
  • When the growing movement of the plant part is against or away from the stimulus, it is called negative tropism.

The tropic movements are most commonly found in the radially symmetrical plant parts such as roots and stems.
The tropic movements help the plants to obtain water and nutrients from the soil and light from the sun that are necessary for their growth and survival.

Chemical Coordination in Plants Types of tropical movements in plants

There are five types of tropical movements in the plants – phototropism, geotropism, hydrotropism, chemotropism and thigmotropism.

1. Phototropism – Movement in response to light.
The growth and movement (orientation) of a plant part in response to the light is called phototropism. For example, movement of sunflowers in the direction of sunlight is phototropism.
If the plant part (like the shoot/stem) orients towards the light then it shows positive phototropism. If the plant part (like its root) moves away from light then it shows negative phototropism.

Chemical Coordination in plants Positive phototropism & Negative phototropism

Positive phototropism             Negative phototropism

The phototropic movements are controlled by growth-regulatory chemical substances (such as auxins) which collect inside the cells farthest away from the light. This causes the plant cells farthest from light to get elongated, leading to an increase in length towards or away from the light source and resulting in curvature.

2. Geotropism – Movement in response to gravity
The growth movement of a plant part in response to gravitational force of the earth is called geotropism. Roots show positive geotropism (grow in the To show phototropism in plants).

Chemical Coordination in Plants Activity 1

To show phototropism in plants.

Chemical Coordination in Plants Procedure

  • Take a conical flask containing water.
  • Take a few freshly germinated bean seeds and suspend these in the conical flask with the help of a loose wire mesh.
  • Place the flask in the cardboard box as shown on open side of the box should face the source of light.
  • Leave the set-up for 3 days and observe.

Chemical Coordination in Plants Observation 1

You will observe that shoots bend towards the light and root away from the light.

  • Now, rotate the flask in such a manner that shoots bend away from the light and roots towards the light. Leave the set-up for a few days and observe.

Chemical Coordination in Plants Observation 2

You will observe that once again shoots turn towards the light and root away from the light.

Chemical Coordination in Plants Conclusion

This shows that the light acts as a stimulus. Shoots respond by bending towards the light (positive phototropism) while roots bend away from the light (negative phototropism).

Chemical Coordination in plants Positive and negative phototropism

Positive and negative phototropism

direction of gravity) while shoots show negative geotropism (grow against a force of gravity). This can be observed if you plant a seedling upside down, the roots tend to grow downwards while the shoot will grow upwards.

Chemical-Coordination-in-plants-Positive-and-negative-geotropism

Positive and negative geotropism

3. Hydrotropism – Movement in response to water
The growth movement of plant parts towards water or moisture is called hydrotropism. The roots always grow towards water, therefore roots are positively hydrotropic. For example, the roots of plants growing in humid soil bend towards a higher relative humidity level.

Chemical Coordination in plants Positive-hydrotropism

Positive hydrotropism

4. Chemotropism – Movement in Response to Chemicals
The growth movement of a plant part due to chemical stimuli is called chemotropism. For example, a pollen tube grows through the style towards ovules in response to certain chemical secretions from stigma.
When the plant part grows towards chemical stimulus, it is positive chemotropism. If it grows away from chemicals, it is negative chemotropism.

5. Thigmotropism – Movement in Response to Touch
The growth movement of a plant part in response to the touch of an object is called thigmotropism. In some plants, when the plant organ touches support, it results in a coiling response to catch and hold the object and tighten its hold. For example, the tendrils 88 of a plant (such as sweet peas and vines)

Chemical-Coordination-in-plants-Thigmotropism

Thigmotropism

 grows towards support, touch it and wind around that support.
Roots have a negative touch response, which means that when they feel an object, they move and grow away from it. This property allows the roots to go through the soil with minimum resistance.

Chemical Coordination in Plants Nastic movements or nasties

The movement of a plant part in response to an external stimulus when occurs in a way that the direction of response is not oriented with respect to the direction of the stimulus, it is called nastic movement. The curvature so produced in these types of movements is because of diffused stimuli and affects the whole plant uniformly. Nastic movements are temporary movements and plant organs revert after the removal of stimulus.

  • When the non-directional movement of a plant part occurs in response to touch, it is called thigmonasty. For example, movement in touch-me-not plant (Mimosa pudica).
  • When the non-directional movement of a plant part (usually petals) occurs in response to light, it is called photo nasty. For example, opening and closing of Dandelion flower in response to light intensity.

The main difference between tropic and nastic movements is that a tropic movement is directional while a nastic movement is non-directional.

The difference between thigmotropism and thigmonasty is given in Table.

Table. Differences between thigmotropism and thigmonasty

Chemical-Coordination-in-plants-Differences-between-thigmotropism-and-thigmonasty

Chemical Coordination in Plants – Plant growth regulators

Plants produce certain chemical substances in their cells which regulate their growth and development. These chemicals are secreted in very minute quantities but have a substantial effect on physiological processes in a plant. Some of these chemicals stimulate plant growth while others retard the rate of growth in plants. Therefore, these chemicals are known as plant growth regulators or plant hormones or phytohormones. They coordinate the activities of the plants by controlling one or the other aspect of growth of the plants.

Types of plant growth regulators

There are five main types of naturally occurring plant hormones or plant growth regulators.

  1. 1. Auxins
  2. Gibberellins
  3. Cytokinins
  4. Ethylene
  5.  Abscisic acid (ABA)

Auxins
Auxins are a group of plant growth regulators which are synthesized in meristematic tissues at the shoot and root tips. Auxins promote cell enlargement and cell differentiation. The most common naturally occurring auxin is indole-3-acetic acid (IAA). The common synthetic auxin is indolebutyric acid (IBA). Auxins are widely used in agricultural and horticultural practices due to their role in plant growth.

Functions

1. Influences plant growth: Auxin is a growth hormone and helps the cells to grow longer. It is synthesized at the shoot and root tips. When the tip of a tendril touches a support, the auxin present in it moves away from the support. Therefore, the side of tendril away from support grows longer and faster. It also curves or bends towards the support and as a result winds around the support.

2. Counter balances root and shoot growth: It has opposite effect on the growth of the stem and roots. It promotes cell growth in shoots and inhibits cell growth in roots.

3. Controls the phototropic behaviour of a plant: When light comes from one side of the plant, auxin diffuses away from the light towards shady side of the shoot. The higher concentration of auxin towards the shady areas stimulates the cells to grow longer and faster and the plant appears to bend towards light.

Chemical-Coordination-in-plants-Auxin-controls-the-phototropic-behaviour-of-a-plant

Auxin controls the phototropic behaviour of a plant

4. Controls the geotropic behaviour of a plant: In a root, extra auxin inhibits growth. In a root, which is growing sideways, more auxin gets accumulated on its lower side. Therefore, the cells on the upper side grow and elongate faster. As a result, the root bends downwards.

Chemical-Coordination-in-plants-Auxin-controls-the-geotropic-behaviour-of-a-plant
Auxin controls the geotropic behaviour of a plant

5. Controls the hydrotropic behaviour of a plant: In a root, more auxin is produced on the side with more moisture. This inhibits the growth on that side and as a result, the root bends towards the moisture.

Chemical-Coordination-in-plants-Auxin-controls-the-hydrotropic-behaviour-of-a-plant

Auxin controls the hydrotropic behaviour of a plant.

6. Induces the formation of seedless fruits without fertilization (known as parthenocarpy) in a number of plants. For example, in tomatoes.

7. Helps in the lengthening of internodes and suppresses the growth of lateral buds.

Gibberellins
Gibberellins are another class of plant growth regulators which produce a variety of physiological responses in plants. These are formed in plastids of leaves of 90 buds, developing embryos and root tips. At present, more than a hundred different gibberellins have been identified. They are denoted as GA₁, GA₂, GA3 and so on. Of these, gibberellic acid (GA3) is the most thoroughly studied.

Functions

  • Gibberellin promotes cell enlargement in the presence of auxins.
  • It delays leaf senescence in a few species of plants.
  • It promotes cell division and stimulates stem elongation and causes plants to grow taller.
  • It stimulates seed germination by breaking seed dormancy.
  • It also helps in seed germination, flowering and fruit growth.
  • It is used in the brewing industry to speed up the malting process.

Cytokinins
Cytokinins are a kind of plant hormones that play a central role during cell cycle and influence many developmental processes. Natural cytokinins are synthesized in regions where rapid cell division occurs, for example, root apices, developing shoot buds, young fruits, etc. It also helps to produce new leaves, chloroplasts and lateral shoot growth.
Cytokinins are produced in roots and transported up through the xylem. They promote tissue growth, and budding I retard plant senescence.

Functions

  • Cytokinin promotes cell division. Therefore, it is present in high concentrations in areas of rapid cell division like fruits and seeds.
  •  It controls cell enlargement and cell differentiation.
  •  Like gibberellins, it also helps in breaking seed dormancy.

Ethylene
Ethylene is a growth-regulatory gaseous hormone. It is formed in all parts of plants but its synthesis occurs maximum during the ripening of some fruits.

Functions

  • Ethylene is a gaseous hormone that has inhibitory effect on growth.
  • It stimulates abscission in flowers and fruits.
  • It strongly promotes the formation of female flowers in monoecious plants like pumpkin and melon.
  • It induces ripening of fruits.
  • It causes downward curvature of leaves (known as epinasty).
  • It induces flowering in mango.
  • It breaks seed and bud dormancy. It initiates the sprouting of potato tubers and germination in peanut seeds.

Abscisic acid (ABA)
Abscisic acid is a weak acid that was first identified in the early 1960s as a growth inhibitor and was originally believed to be involved in abscission. It is also called a stress hormone as it acts as a mediator in controlling plant responses to environmental stresses. It is produced in mature green leaves and in fruits.

Functions

  • Abscisic acid is a growth-inhibiting hormone and inhibitor of plant metabolism.
  • It promotes wilting of leaves.
  • It promotes the dormancy of seeds and buds. It acts as an inhibitor of seed germination.
  • It prevents loss of water by causing stomatal closure.

Chemical Coordination in Plants Summary

  • Plants do not have a nervous system but they still respond to internal and external changes in the environment around them.
  • The function of control and coordination in plants is performed by chemical substances called hormones or plant growth regulators.
  • Any change in the environment to which an organism responds and reacts is called a stimulus. Response to stimuli is a characteristic property of each living organism.
  • Plant movements in response to stimuli can be of two types: tropic movements and nastic movements.
  • A growth response that results in the movement of plant parts towards or away from stimuli is called tropism.
  • When the growing movement of the plant part is towards the stimulus, it is called positive tropism. When the growing movement of the plant part is against or away from the stimulus, it is called negative tropism.
  • There are five types of tropisms found in the plant phototropism, geotropism, hydrotropism, chemotropism and thigmotropism.
  • The growth movement of a plant part in response to the light is called phototropism.
  • The growth movement of a plant part in response to gravitational force of the earth is called geotropism.
  • The growth movement of a plant part towards water or moisture is called hydrotropism.
  • The growth movement of a plant part due to chemical stimuli is called chemotropism.
  • The growth movement of a plant part in response to the touch of an object is called thigmotropism.
  • The movement of a plant part in response to an external stimulus when occurs in a way that the direction of response is not based on the direction of stimulus, it is called nastic movement.
  • Plants produce certain chemical substances in their cells which regulate their growth and development. These chemicals are known as plant growth regulators or plant hormones or phytohormones.
  • Auxin is a growth hormone and helps the cells to grow longer, and controls the phototrophic and the geotropic behaviour of a plant.
  • Gibberellin promotes cell enlargement, and cell division and stimulates stem elongation
  • Cytokinins play a central role during the cell cycle and influence numerous developmental programmes.
  • Ethylene is a gaseous hormone that has an inhibitory effect on growth and induces ripening of fruits.
  • Abscisic acid is a growth-inhibiting hormone and inhibitor of plant metabolism. It promotes wilting of leaves.