Solutions-Class-12-Biology-Chapter-8-Respiration and Circulation-Maharashtra Board

Respiration and Circulation

Maharashtra Board-Class-12th-Biology-Chapter-8


Question 1. Choose the correct alternatives from those given below and complete the statements.

(1) The muscular structure that separates the thoracic and abdominal cavity is  __.

(a) pleura

(b) diaphragm

(c) trachea

(d) epithelium

Answer :

(b) diaphragm

(2) What is the minimum number of plasma membrane that oxygen has to diffuse across to pass from air in the alveolus to haemoglobin inside a R.B.C.?

(a) Two

(b) Three

(c) Four

(d) Five

Answer :

(a) Two

(3) ________ is a sound producing organ,

(a) Larynx

(b) Pharynx

(c) Tonsils

(d) Trachea

Answer :

(a) Larynx

(4) The maximum volume of gas that is inhale during breathing in addition to T.V is _____.

(a) residual volume

(b) I.R.V.

(c) G.R.V.

(d) vital capacity

Answer :

(b) I.R.V.

(5) ________ muscles contract when the external intercostal muscles contract

(a) Internal abdominal

(b) Jaw

(c) Muscles in bronchial walls

(d) Diaphragm

Answer :

(d) Diaphragm

(6) Movement of cytoplasm in unicellular organisms is called _____.

(a) diffusion

(b) cyclosis

(c) circulation.

(d) thrombosis.

Answer :

(b) cyclosis

(7) Which of the following animals do not have closed circulation?

(a) Earthworm.

(b) Rabbit

(c) Butterfly

(d) Shark

Answer :

(c) Butterfly

(8) Diapedesis is performed by ____.

(a) erythrocytes

(b) thrombocytes

(c) adipocytes

(d) leucocytes

Answer :

(d) leucocytes

(9) Pacemaker of heart is _____.

(a) SA node

(b) AV node

(c) His bundle

(d) Purkinje fibers

Answer :

(a) SA node

(10) Which of the following is without nucleus?

(a) Red blood corpuscle

(b) Neutrophill

(c) Basophill

(d) Lymphocyte

Answer :

(a) Red blood corpuscle

(11) Cockroach shows which kind of circulatory system?

(a) Open

(b) Closed

(c) Lymphatic

(d) Double

Answer :

(a) Open

(12) Diapedesis can be seen in ______ cell.

(a) RBC

(b) WBC

(c) Platelet

(d) neuron

Answer :

(b) WBC

(13) Opening of inferior vena cava is guarded by ______.

(a) bicuspid valve

(b) tricuspid valve

(c) Eustachian valve

(d) Thebesian valve

Answer :

(c) Eustachian valve

(14)  _______ wave in ECG represent atrial depolarization.

(a) P

(b) QRS complex

(c) Q

(d) T

Answer :

(a) P

(15) The fluid seen in the intercellular spaces in Human is _________

(a) blood

(b) lymph

(c) interstitial fluid

(d) water

Answer :

(b) lymph

Question 2. Match the Respiratory surface to the organism in which it is found.

Respiratory surface Organism
Plasma membrane Insect
Lungs Salamander
External gills Bird
Internal Gills Amoeba
Trachea Fish

Answer :

Respiratory surface Organism
Plasma membrane Amoeba
Lungs Bird
External gills Salamander
Internal Gills Fish
Trachea Insect

Question 3. Very short answer questions.

(1) Why does trachea have ‘C’ shaped rings of cartilage?

Answer :

Trachea is supported by ‘C’-shaped rings of cartilage which prevent it from collapsing and always keep it open.

(2) Why is respiration in insect called direct respiration?

Answer :

Respiration in insect is called direct because tracheal tubes exchange O2 and CO2 directly with the haemocoel which then exchange them with tissues.

(3) Why is gas exchange very rapid at alveolar level.

Answer :

Due to the huge surface area that the lungs' numerous alveoli (about 700 million of them) provide for gaseous exchange, gas exchange occurs at the alveolar level very quickly.

(4) Name the organ which prevents the following the entry of food into the trachea while eating.

Answer :

Epiglottis prevents the entry of food into the trachea while eating.

Question 4. Short answer questions.

(1) Why is it advantageous to breathe through the nose than through the mouth?

Answer :

Breathing through the nose is preferable than breathing through the mouth for the following reasons:

  • Because the nostrils are smaller than the mouth, air expelled through the nose causes a backflow of air into the lungs.
  • Because we exhale more slowly through our noses than through our mouths, our lungs have more time to extract oxygen from the air we've already inhaled.
  • The hairs inside the nostrils filter out any dust particles and microorganisms in the air, allowing only clean air to pass through.
  • As air enters our body, it warms and humidifies in our nostrils; however, breathing through the mouth can dry up the oral cavity, leading to bad breath, gum disease, and tooth decay.

(2) Identify the incorrect statement and correct it,

(a) A respiratory surface area should have a large surface area.

(b) A respiratory surface area should be kept dry.

(c) A respiratory surface area should be thin, may be 1mm or less.

Answer :

Statement (a) and (c) are correct statements.

Statement (b) is incorrect : A respiratory surface area should be kept moist, is the correct statement.

(3) Given below are the characteristics of some modified respiratory movement. Identify them.

(a) Spasmodic contraction of muscles of expiration and forceful expulsion of air through nose and mouth.

 (b) An inspiration followed by many short convulsive expiration accompanied by facial expression.

Answer :

(a) Sneezing.

(b) Laughing, crying.

(4) Write a note on blood plasma.

Answer :

  • Plasma is a straw-colored, somewhat alkaline sticky fluid component of blood that contains 90-92% water and 8- 10% soluble proteins.
  • The plasma proteins that make up 7% of the plasma include serum albumin, serum globulin, heparin, fibrinogen, and prothrombin.
  • The nutrients dissolved in plasma are glucose, amino acids, fatty acids, and glycerol.
  • Plasma contains nitrogenous wastes (urea, uric acid, ammonia, and creatinine) as well as breathing gases (oxygen and carbon dioxide).
  • Plasma also transports enzymes and hormones.
  • Inorganic minerals such as bicarbonates, chlorides, phosphates, and sodium, potassium, calcium, and magnesium sulphates are also present in plasma.

(5) Explain blood clotting in short.

Answer :

Blood clotting/ coagulation of blood : Active anticoagulants like heparin and antithrombin are present in the intact blood vessels. But upon the rupture of a blood vessel, bleeding starts. The fluid blood is converted into semisolid jelly by the process of blood coagulation or clotting.

The clotting of blood is a complicated process in which many factors (12 clotting factors) present in plasma and tissues are involved.

The event that take place during blood clotting are as follows :

  • Release of thromboplastin from extrinsic source in tissue and intrinsic source in plasma at injured site through a step-Wise (cascade process) process.
  • Formation of enzyme prothrombinase in the blood.
  • Conversion of prothrombin into thrombin by prothrombinase.
  • Conversion of fibrinogen into fibrin by thrombin.
  • Formation of mesh by the fibrin fibres forming the clot.
  • The normal clotting time is 2 to 8 minutes.

(6) Describe pericardium.

Answer :

  • The pericardium is a double-layered peritoneum that surrounds the heart. It is made up of two layers: fibrous pericardium and serous pericardium.
  • Fibrous pericardium is the outside double-layered membrane with stiff, inelastic fibrous connective tissue, whereas serous pericardium is the interior double-layered membrane. It has an outer parietal layer and an interior visceral layer.
  • The serous pericardium's parietal layer is on the inner side of the fibrous pericardium.
  • The visceral layer, also known as epicardium, attaches to the heart and forms an outer covering over the heart.
  • The pericardial gap contains pericardial fluid, which is found between the parietal and visceral layers of serous pericardium.

(7) Describe valves of human heart.

Answer :

Human heart has following main valves :

  • Tricuspid valve : Tricuspid valve is present between the right atrium and right ventricle. It has three cusps or flaps. It prevents the backflow of blood into right atrium.
  • Bicuspid valve : Bicuspid valve, also called mitral valve is present between the left atrium and left ventricle. It has two flaps. It prevents the backflow of blood in left atrium. Both tricuspid and bicuspid valves are attached to papillary muscles with tendinous chords or chordate tendinae to prevent valves from turning back into atria at the time of systole.
  • Semilunar valve : These are present at the opening of Pulmonary artery and systemic aorta. They prevent the back flow of blood when ventricles undergo systole.
  • Thebesian valve : Thebesian valve is present at the opening of coronary sinus.
  • Eustachian valve : Eustachian valve is present at the opening of inferior vena cava.

(8) What is role of papillary muscles and chordae tendinae in human heart?

Answer :

  • Papillary muscles are muscular ridges that run along the inner surface of the ventricles and are big and well developed.
  • The chordae tendinae connect the bicuspid and tricuspid valves to the papillary muscles of the ventricle.
  • Chordae tendinae are inelastic fibers found in the lumen of ventricles that prevent valves from turning back into the atria during ventricle contraction and govern the opening and closure of bicuspid and tricuspid valves.

 (9) Explain in brief the factors affecting blood pressure.

Answer :

  • Cardiac output: The average cardiac output is 5 lit/min. Systolic pressure rises as cardiac output rises.
  • Peripheral resistance: The diameter of blood arteries determines peripheral resistance. Vasopressin-induced decreases in arteriole and capillary diameter result in an increase in peripheral resistance and, as a result, an increase in blood pressure.
  • Blood volume: Loss of blood in accidents reduces blood volume, causing a drop in blood pressure.
  • Viscosity of blood : Blood pressure is directly proportional to viscosity of blood.
  • Age : Blood pressure increases with age due to increase in inelasticity of blood vessels.
  • Venous return : Amount of blood brought to the heart via the veins per unit time is called the venous return and it is directly proportional to blood pressure.
  • Length and diameter of blood vessels : Blood pressure is directly proportional to the total length of the blood vessel. Blood pressure can also be affected by vasoconstriction or vasodilation.
  • Gender: Females have slightly lower BP than males of her age before menopause. However, the risk of high B. P. increases in the females after menopause sets in.

Question 5. Give scientific reason.

(1) Closed circulation is more efficient than open circulation.

Answer :

  • When compared to open circulation, closed circulation significantly improves the speed, precision, and efficiency of circulation.
  • The blood flows more quickly, and it takes less time to circulate through the closed system and return to the heart.
  • This speeds up the supply and removal of materials to and from the tissues.

(2) Human heart is called as myogenic and autorhythmic.

Answer :

  • Because the drive for the heart's rhythmic movement occurs within the heart, it exhibits autorhythmicity. This type of heart is known as myogenic.
  • During development, certain heart muscle fibers become autorhythmic (self-excitable) and begin to generate impulses.
  • These autorhythmic fibers provide two key functions: they operate as a pacemaker and set the rhythm for the heart, and they also form a conducting system for nerve impulse conduction throughout the heart muscles.
  • ln open circulation, there are no blood vessels such as arteries or veins, to pump the blood. Therefore, the blood pressure is very low.
  • Organisms with an open circulatory system typically have a relatively high volume of hemolymph and low blood pressure. Closed circulation is thus more efficient than open circulation.

(3) Person who has undergone heart transplant needs lifetime supply of immunosupressants.

Answer :

A person who has had a heart transplant requires immunosuppressants for the rest of their lives since organ rejection is a constant risk.

Keeping the immune system from attacking the transplanted organ necessitates a steady supply of immunosuppressive medications. These medications aid in preventing the immune system from attacking ("rejecting") the donor organ. These medicines are typically used for the rest of one's life in order to preserve a transplanted organ.

(4) Arteries are thicker than veins.

Answer :

  • Arteries have relatively thick walls to withstand the high pressure of blood ejected from the heart. Arteries expand when the pressure increases as the heart pushes blood out but recoil (shrink) when the pressure decreases when the heart relaxes between heartbeats.
  • Veins, on the other hand, have thinner walls and larger lumen veins do not require thick walls because they do not have to withstand high pressure like arteries. Furthermore, because veins transport relatively low pressure blood, they are commonly equipped with valves to promote unidirectional flow of blood towards the heart.

(5) Left ventricle is thick than all other chambers of heart.

Answer :

  • The left ventricle circulates oxygenated blood throughout the body. As a result, the blood pressure in the left ventricle is higher.
  • The right ventricle transfers deoxygenated blood to the lungs for oxygenation. This does not increase pressure, and the lungs are close to the heart.
  • Because of these functional variations between the two ventricles, the left ventricle has a thicker wall than the right ventricle.

Question 6. Distinguish between :

(1) Open and closed circulation.

Answer :

Open circulation Closed circulation
In open circulation, blood flows through large open spaces and channels called lacunae and haemocoels among the tissues. In closed circulation, blood flows through a network of blood vessels all over the body.
Tissues are in direct contact with the blood. Blood does not come in direct contact with tissue.
Blood flows with low pressure and usually does not contain any respiratory pigment like haemoglobin. Blood flows with high pressure and contains respiratory pigment like haemoglobin.
Exchange of material takes place directly between blood and cells or tissues of the body. Exchange of material takes place between blood and body tissues through an intermediate fluid called lymph.
Volume of blood flowing through a tissue cannot be controlled as blood flows out in open space. Volume of blood can be regulated by the

contraction and relaxation of the smooth

muscles of the blood vessels.

Open circulatory system is found in arthropods and some molluscs. Closed circulatory system is found in annelids, echinoderms and all vertebrates.

(2) Artery and vein.

Answer :

Artery Vein
Carrying blood from the heart to other parts of the body. Canying blood from the different parts of the body to the heart.
Arteries are thick walled blood vessels, situated in deep layers in the body. Veins are thin walled blood vessels, situated superficially in the body.
Arteries do not have valves. Veins have valves.
Tunica adventitia, the outermost layer of arteries is thick and elastic. Tunica externa, the outermost layer of veins is thin.
Tunica media is very thick and contain elastic fibres. Tunica media is thin layer and contain

involuntary muscle fibres.

The lumen of arteries is small. The lumen of the veins is very spacious.
With the exception of pulmonary arteries, all other arteries carry oxygenated blood. With the exception of pulmonary veins, all other veins carry deoxygenated blood.
Blood in the arteries show high blood pressure. Blood in the veins show lesser blood pressure.

(3) Blood and lymph.

Answer :

Blood Lymph
All three types of blood cells—RBCs, WBCs, and blood platelets—as well as blood plasma with proteins are found in blood. Blood plasma without blood proteins, RBCs, and platelets are found in lymph, along with lymphocytes.
Red in colour due to presence of RBCs. Light yellow in colour and does not contain RBCs.
Carries oxygen in the body. Does not carry oxygen.
The flow of blood in blood vessels is fast. The flow of lymph in lymph capillaries is slow.
Lymphocytes are present. Lymphocytes are present, more in number than those present in the blood.

(4) Blood capillary and lymph capillary.

Answer :

Blood capillary Lymph capillary
Reddish, easy to observe. Colourless, difficult to observe.
Joined to arterioles at one end and to venules at another end. Blind (closed at the tip).
Narrower than lymph capillaries. Wider than blood capillaries.
Wall consists of normal endothelium and

basement membrane.

Wall consists of thin endothelium and poorly developed basement membrane.
Contains red blood. Contains colourless lymph.
Have relatively high pressure. Have relatively low pressure.

(5) Intrinsic and extrinsic process of clotting.

Answer :

Intrinsic process Extrinsic process
The intrinsic pathway requires only clotting factors found within the blood itself — in particular, clotting factor XII (Hageman factor) from the platelets. The extrinsic pathway is initiated by factors external to the blood, in the tissues adjacent to damaged blood vessel — in particular, it is initiated by clotting factor III, thromoboplastin

from the damaged tissues.

It is a longer, multistep process and it takes a little longer for the blood to clot by this mechanism. It involves fewer chemical reaction steps and produce a clot a little more quickly than the intrinsic pathway.

Question 7. Long answer questions.

(1) Smita was working in a garage with the doors closed and automobiles engine running. After some time she felt breathless and fainted. What would be the reason? How can she be treated?

Answer :

  • Because Smita and John were working with the car engine running in a closed garage, they must have been poisoned by carbon monoxide.
  • Carbon monoxide (CO) is a very hazardous gas created when fuels in automotive engines burn incompletely.
  • Because haemoglobin has a high affinity for carbon monoxide, it rapidly mixes with it to form the stable molecule carboxyhaemoglobin. As a result, there is less haemoglobin available for oxygen delivery, depriving cells of oxygen.
  • Carbon monoxide poisoning frequently causes a throbbing headache, sleepiness, shortness of breath, and fainting. Carbon monoxide poisoning usually results in unconsciousness, convulsions, circulatory failure, coma, and death in severe cases.

The breathless persons can be treated by following method :

  • Oxygen treatment : The best way to treat carbon monoxide poisoning is to breathe in pure oxygen (high-dose oxygen treatment)
  • Oxygen chamber : Doctor may temporarily place her in a pressurized oxygen chamber (also known as a hyperbaric oxygen chamber).

(2) Shreyas went to a garden on a wintry morning. When he came back, he found it difficult to breath and started wheezing. What could be the possible condition and how can he be treated?

Answer :

  • It suggests that Shreyas is experiencing allergic responses. On his journey to the garden, he may have come into contact with allergens such as pollen, dust, pet dander, or other environmental pollutants. Alternatively, Shreyas may already be an Asthma patient, and his symptoms may have worsened owing to the cold weather.
  • When a person is allergic to a substance, such as pollen, his immune system reacts to it as if it were foreign and dangerous, and attempts to eliminate it.
  • In response to these allergens, the body produces and releases molecules known as IgE antibodies. These IgE antibodies bind to most cells in the body that produce histamine. Histamine is the primary cause of pollen allergy symptoms such as trouble breathing, wheezing, sneezing, itchy throat, and so on.

Treatment : There are several drugs to treat the allergic reactions :

  • Antihistamines such as cetirizine or diphenhydramine.
  • Decongestants, such as pseudoephedrine or oxymetazoline.
  • Medications that combine an antihistamine and decongestant such as Actifed and Claritin-D.

(3) Why can you feel a pulse when you keep a finger on the wrist or neck but not when you keep them on a vein?

Answer :

  • When the heart contracts, pressure is created that pushes blood out of the heart. This pressure behaves similarly to a wave. The pulse you feel is caused by this "wave" of pressure. However, this pressure is not consistent.
  • Maximum pressure in the arteries occurs as the heart pumps blood out of it during systole. When this pressure reaches capillaries, it weakens significantly, and the veins farthest from the heart are under less pressure. Because of the low pressure, veins include valves to prevent blood backflow.
  • The pressure in the arteries can be felt every time the heart beats, especially in arteries which come to surface of the body like that of the wrist and neck but not in the veins.
  • The pressure in veins is always weaker than in arteries, resulting in a weaker pulse to the point that it is undetectable by touch alone.
  • Owing to this, when we keep finger on the arteries of wrist or neck, we feel a pulse but not when we keep it on a vein.

(4) A man’s pulse rate is 68 and cardiac output is 5500 cm3.Find the stroke volume.

Answer :

Cardiac output is the volume of blood pumped out per min for a normal adult human being it is calculated as follows :

Cardiac output = Heart rate x Stroke volume

Given : Cardiac output = 5500 cm3

Pulse rate = Heart rate = 68

∴ Cardiac output = Heart rate x Stroke volume

 Stroke volume = Cardiac output/Heart rate = 5500/68 = Approx. 80. 

∴ Stroke volume is 80 ml.

(5) Which blood vessel of the heart will have the maximum content of Oxygen and why?

Answer :

  • The Aorta, which exits the heart from the left ventricle, carries the most oxygen.
  • Deoxygenated blood is oxygenated in the pulmonary capillaries that surround the lungs' alveoli. The four pulmonary veins gather oxygenated blood from the lungs.
  • These pulmonary veins transport oxygenated blood to the heart's left atrium. During atrial systole, blood is transported to the left ventricle.
  • During ventricular systole, the left ventricle pumps oxygenated blood to the aorta.
  • As a result, the aorta has the highest oxygen content.

(6) If the duration of the atrial systole is 0.1 sec and that of complete diastole is 0.4 sec, then how does one cardiac cycle complete in 0.8 sec?

Answer :

  • The time duration required to complete one cardiac cycle is 0.8 second.
  • Cardiac cycle is divided into three important phases, viz, atrial systole, ventricular systole and joint diastole.
  • Atrial systole in normal condition lasts for 0.1 second, ventricular systole follows atrial systole and lasts for 0.3 second whereas joint diastole or complete diastole lasts for about 0.4 second.
  • In this way one cardiac cycle is completed in 0.8 second.

(7) How is blood kept moving in the large veins of the legs?

Answer :

  • The heart pushes blood with pressure into the aorta while it is in systole. This pressure causes the blood to circulate throughout the body in its entirety. After nourishing the higher sections of the body, the aorta gives rise to the dorsal aorta. It then splits into two arteries, each of which enters one leg. Blood pressure and gravity both help to force the blood to travel through the legs.
  • In addition, the muscles in legs help transport blood back to our heart. As the muscles of our body contract and relax to move our limbs, they squeeze the blood in veins and the blood is then pushed towards the heart.
  • The veins in legs also have valves to keep this process going and prevent blood from flowing back down towards the feet.
  • In this way blood is kept moving in the large veins of the legs.

(8) Describe histological structure of artery, vein and capillary.

Answer :

Histological structure of artery and vein.

  • An artery is a blood vessel with a thick wall that transports oxygenated blood. (The pulmonary artery, which transports the heart's deoxygenated blood to the lungs for oxygenation, is an exception.)
  • All of the arteries leave the heart and carry blood to other organs.
  • There are three layers in each artery: the tunica externa, tunica media, and tunica interna. The thickest layer is called the tunica externa or adventitia. It is the outermost covering composed of collagen and elastic fibers in connective tissue.
  • Tunica media is the middle coat made up of smooth muscle fibres and elastic fibres. It withstands high blood pressure during ventricular systole. It is also thick.
  • Tunica interna or intima is the innermost coat made of endothelium and elastic layer.

Histology of Capillaries :

  • Capillaries are the smallest and thinnest blood vessels. Capillaries are formed by the division and re-division of the arterioles.
  • The wall of the capillary is made up of endothelium or squamous epithelium.
  • The capillary wall is permeable to water and dissolved substances.
  • Exchange of respiratory gases, nutrients, excretory products, etc. takes place through the capillary wall.
  • Capillaries unite to form venules.

(9) What is blood pressure? How is it measured? Explain factors affecting blood pressure.

Answer :

Blood pressure :

  • Blood pressure is the force that blood is applying to the blood vessel wall.
  • Blood pressure in the arteries is the force that the blood is exerting against the artery wall.
  • Systolic and diastolic blood pressure are the two words used to define blood pressure.
  • The pressure placed on the artery wall during ventricular contraction (systole) is known as systolic blood pressure. The typical reading for a healthy adult is 120 mmHg.
  • The pressure on the artery wall during ventricular relaxation (diastole) is known as diastolic blood pressure. It is 80 mmHg for an adult who is normally healthy.
  • P = SP/DP = 120/80 mmHg. Blood pressure is normally written as 120/80
  • Difference between systolic and diastolic pressure is called pulse pressure normally, it is 40 mmHg.

Measurement of blood pressure :

  • Blood pressure is measured with the help of an instrument called sphygmomanometer.
  • The instrument consists of inflatable rubber bag cuff covered by a cotton cloth. It is connected with the help of tubes to a mercury manometer on one side and a rubber bulb on the other side.
  • During measurement, the person is asked to lie in a sleeping position. The instrument is placed at the level of heart and the cuff is tightly wrapped around upper arm.
  • The cuff is inflated until external pressure blocks the brachial artery. Then, until the first pulsatile sound is made, the pressure in the cuff is gradually reduced. The pressure shown in the manometer at this time is systolic pressure. Korotkoff sounds are those made during this blood pressure test.
  • The cuff's pressure is progressively reduced until there is no longer any pulsatile sound because of the blood is flowing smoothly. The pressure shown in the manometer at this time is diastolic, and the ideal blood pressure (normal) level is 120/80 mmHg.

(10) Describe human blood and give its functions.

Answer :

Blood Composition :

  • Blood is a red coloured fluid connective tissue derived from embryonic mesoderm.
  • It has two components —the fluid plasma (55%) and the formed elements i.e. blood cells (44%).
  • Plasma is a straw coloured, slightly alkaline and viscous fluid having 90% water and 10% solutes such as proteins, nutrients, nitrogenous wastes, salts, hormones, etc.
  • Blood corpuscles are of three types, viz. erythrocytes (RBCs), White blood corpuscles (WBCs) and thrombocytes (platelets).

(1) Red blood corpuscles or Erythrocytes :

Erythrocytes are the most abundant cells in the human body. They are circular, biconcave and enucleated (in camel and llama they are nucleated).

  • Erythrocytes or red blood corpuscles. They are circular, biconcave, enucleated cells.
  • The RBC size : 7 um in diameter and 2.5 pm in thickness.
  • The RBC count: 5.1 to 5.8 million RBCs/cu mm of blood in an adult male and 4.3 to 5.2 million/cu mm in an adult female.
  • The average life span of RBC : 120 days.
  • RBCs are formed by the process of erythropoiesis. In foetus, RBC formation takes place in liver and spleen whereas in adults it occurs in red bone marrow.
  • The old and worn out RBCs are destroyed in liver and spleen.
  • Polycythemia is an increase in number of RBCs While erythrocytopenia is decrease in their (RBCs) number.
  • Functions : RBCs transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs. They maintain blood pH as haemoglobin acts as a buffer. They also maintain the viscosity of the blood.

(2) White blood corpuscles / Leucocytes :

  • Leucocytes or White Blood Corpuscles (WBCs) are colouriess, nucleated, amoeboid and phagocytic cells.
  • Their size ranges between 8 to 15 um. Total WBC count is 5000 to 9000 WBCs/cu mm of blood. The average life span of a WBC is about 3 to 4 days.
  • They are formed by leucopoiesis in red bone marrow, spleen, lymph nodes, tonsils, thymus and Payer’s patches, whereas the dead WBCs are destroyed by phagocytosis in blood, liver and lymph nodes.

Leucocytes are mainly divided into two types, viz., granulocytes and agranulocytes.

Granulocytes : Granulocytes are cells with granular cytoplasm and lobed nucleus. Based on their staining properties and shape of nucleus, they are of three types, viz. neutrophils, eosinophils and basophils.

(I) Neutrophils :

  • In neutrophils, the cytoplasmic granules take up neutral stains.
  • Their nucleus is three to five lobed.
  • It may undergo changes in structure hence they are called polymorphonuclear leucocytes or polyrnorphs.
  • Neutrophils are about 70% of total WBCs.
  • They are phagocytic in function and engulf microorganisms.

(II) Eosinophils or acidophils :

  • Cytoplasmic granules of eosinophils take up acidic dyes such as eosin. They have bilobed nucleus.
  • Eosinophils are about 3% of total WBCs.
  • They are non-phagocytic in nature.
  • Their number increases (i.e. eosinophilia) during allergic conditions.
  • They have antihistamine property

(III) Basophils :

  • The cytoplasmic granules of basophils take up basic stains such as methylene blue.
  • They have twisted nucleus.
  • In size, they are smallest and constitute about 0.5% of total WBCs.
  • They too are non-phagocytic.
  • Their function is to release heparin which acts as an anticoagulant and histamine that is involved in inflammatory and allergic reaction.

Agranulocytes : There are two types of agranulocytes, viz. monocytes and lymphocytes. Agranulocytes do not show cytoplasmic granules and their nucleus is not lobed. They are of two types, viz. lymphocytes and monocytes.

(I) Lymphocytes :

  • Agranulocytes with a large round nucleus are called lymphocyte.
  • They are about 30% of total WBCs.
  • Agranulocytes are responsible for immune response of the body by producing antibodies.

(II) Monocytes :

  • Largest of all WBCs having large kidney shaped nucleus are monocytes. They are about 5% of total WBCs.
  • They are phagocytic in function.
  • They can differentiate into macrophages for engulfing microorganisms and removing cell debris. Hence they are also called scavengers.
  • At the site of infections they are seen in more enlarged form.

(3) Thrombocytes/Platelets :

  • Thrombocytes or platelets are non-nucleated, round and biconvex blood corpuscles.
  • They are smallest corpuscles measuring about 2.5 to 5 mm in diameter with a count of about 2.5 lakhs/cu mm of blood.
  • Their life span is about 5 to 10 days.
  • Thrombocytes are formed from megakaiyocytes of bone marrow. They break from these cells as fragments during the process of thrombopoiesis.
  • Thrombocytosis is the increase in platelet count while thrombocytopenia is decrease in platelet count.
  • Thrombocytes possess thromboplastin which helps in clotting of blood.
  • Therefore, at the site of injury platelets aggregate and form a platelet plug. Here they release thromboplastin due to which further, blood clotting reactions take place.

Functions of blood :

  • Transport of oxygen and carbon dioxide
  • Transport of food
  • Transport of waste product
  • Transport of hormones
  • Maintenance of pH
  • Water balance
  • Transport of heat
  • Defence against infection
  • Temperature regulation
  • Blood clottingcoagulation
  • Helps in healing

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