15.8 Exercise Problems

Q1. Name the components of the formed elements in the blood and mention one major function of each of them.

Answer: The component elements in the blood are:
(1) Erythrocytes: They are the most abundant cells and contain the red pigment called hemoglobin. They carry oxygen to all parts of the body. Red blood cells are produced continuously in some parts of the body such as the marrow of long bones, ribs, etc. There are about 4-6 million RBCs per cubic millimeter of blood.
(2) Leukocytes: Leucocytes are colorless cells. These cells do not contain hemoglobin. They are the largest cells of the body and are divided into two main categories.
(a) Granulocytes: These leucocytes have granules in their cytoplasm and include neutrophils, eosinophils, and basophils. Neutrophils are phagocytic cells that protect the body against various infecting agents. Eosinophils are associated with allergic reactions, while basophils are involved in inflammatory responses.
(b) Agranulocytes: Lymphocytes and monocytes are agranulocytes. Lymphocytes generate immune responses against infecting agents, while monocytes are phagocytic in nature.
(3) Platelets: Platelets are small irregular bodies present in the blood. They contain essential chemicals that help in clotting. The main function of platelets is to promote clotting.

Q2. What is the importance of plasma proteins?

Answer: Plasma is the colorless fluid of blood that helps in the transport of food, \(\mathrm{CO}_2\), waste products, and salts. It constitutes about \(55 \%\) of blood. About \(6.8 \%\) of the plasma is constituted by proteins such as fibrinogens, globulins, and albumins. Fibrinogen is a plasma glycoprotein synthesized by the liver. It plays a role in the clotting of blood. Globulin is a major protein of the plasma. It protects the body against infecting agents. Albumin is a major protein of the plasma. It helps in maintaining the fluid volume within the vascular space.

Q3. Match Column I with Column II

\(
\begin{array}{|l|l|}
\hline \text { Column I } & \text { Column II } \\
\hline \text { (a) Eosinophils } & \text { (1) Coagulation } \\
\hline \text { (b) RBC } & \text { (2) Universal recipient } \\
\hline \text { (c) AB group } & \text { (3) Resist infections } \\
\hline \text { (d) Platelets } & \text { (4) Contraction of heart } \\
\hline \text { (e) Systole } & \text { (5) Gas transport } \\
\hline
\end{array}
\)

Answer: 

\(
\begin{array}{|l|l|}
\hline \text { Column I } & \text { Column II } \\
\hline \text { (a) Eosinophils } & \text { (1) Resist infections} \\
\hline \text { (b) RBC } & \text { (2) Gas transport } \\
\hline \text { (c) AB group } & \text { (3) Universal recipient } \\
\hline \text { (d) Platelets } & \text { (4) Coagulation } \\
\hline \text { (e) Systole } & \text { (5) Contraction of heart } \\
\hline
\end{array}
\)

Q4. Why do we consider blood as a connective tissue?

Answer: Connective tissues have cells scattered throughout an extracellular matrix. They connect different body systems. Blood is considered as a type of connective tissue because of two reasons.

• Like the other connective tissues, blood is mesodermal in origin.
• It connects the body systems, transports oxygen and nutrients to all the parts of the body, and removes waste products. Blood has an extra-cellular matrix called plasma, with red blood cells, white blood cells, and platelets floating in it.

Q5. What is the difference between lymph and blood?

Answer: 

Lymph	Blood
1. It is a colorless fluid that does not contain RBCs.	1. It is a red-colored fluid that contains RBCs.
2. It contains plasma and a lesser number of WBCs and platelets.	2. It contains plasma, RBCs, WBCs, and platelets.
3. It helps in body defense and is a part of the immune system.	3. It is associated with the circulation of oxygen and carbon dioxide.
4. Its plasma lacks proteins.	4. Its plasma has proteins, calcium, and phosphorus.
5. It transports nutrients from the tissue cells to the blood, through lymphatic vessels.	5. It transports nutrients and oxygen from one organ to another.
6. The flow of lymph is slow.	6. The flow of blood in the blood vessels is fast.

Q6. What is meant by double circulation? What is its significance?

Answer: Double circulation is a process during which blood passes twice through the heart during one complete cycle. This type of circulation is found in amphibians, reptiles, birds, and mammals. However, it is more prominent in birds and mammals as in them the heart is completely divided into four chambers – the right atrium, the right ventricle, the left atrium, and the left ventricle.
The movement of blood in an organism is divided into two parts:

• Systemic circulation
• Pulmonary circulation
  Systemic circulation: involves the movement of oxygenated blood from the left ventricle of the heart to the aorta. It is then carried by the blood through a network of arteries, arterioles, and capillaries to the tissues. From the tissues, the deoxygenated blood is collected by the venules, veins, and vena cava, and is emptied into the left auricle.
  Pulmonary circulation: involves the movement of deoxygenated blood from the right ventricle to the pulmonary artery, which then carries blood to the lungs for oxygenation. From the lungs, the oxygenated blood is carried by the pulmonary veins into the left atrium. Hence, in double circulation, blood has to pass alternately through the lungs and the tissues.
  Significance of double circulation:
  The separation of oxygenated and deoxygenated blood allows a more efficient supply of oxygen to the body cells. Blood is circulated to the body tissues through systemic circulation and to the lungs through the pulmonary circulation.

Q7. Write the differences between:
(a) Blood and Lymph
(b) Open and Closed system of circulation
(c) Systole and Diastole
(d) P-wave and T-wave

Answer: (a) Blood and lymph

Blood	Lymph
1. Blood is a red-colored fluid that contains RBCs.	1. Lymph is a colorless fluid that lacks RBCs.
2. It contains plasma, RBCs, WBCs, and platelets. It also contains proteins.	2. It contains plasma and a lesser number of WBCs and platelets. It lacks proteins.
3. Blood transports nutrients and oxygen from one organ to another.	3. Lymph plays a role in the defensive system of the body. It is a part of the immune system.

(b) Open and closed systems of circulation

The open system of circulation	The closed system of circulation
1. In this system, blood is pumped by the heart, through large vessels, into body cavities called sinuses.	1. In this system, blood is pumped by the heart, through a closed network of vessels.
2. The body tissues are in direct contact with blood.	2. The body tissues are not in direct contact with blood.
3. Blood flows at low pressure. Hence, it is a slower and less efficient system of circulation.	3. Blood flows at high pressure. Hence, it is a faster and more efficient system of circulation.
4. The flow of blood is not regulated through the tissues and organs.	4. The flow of blood can be regulated by valves.
5. This system is present in arthropods and mollusks.	5. This system is present in annelids, echinoderms, and vertebrates.

(c) Systole and diastole 

Systole	Diastole
1. It is the contraction of the heart chambers to drive blood into the aorta and the pulmonary artery.	1. It is the relaxation of the heart chambers between two contractions. During diastole, the chambers are filled with blood.
2. Systole decreases the volume of the heart chambers and forces the blood out of them.	2. Diastole brings the heart chambers back into their original sizes to receive more blood.

(d) P-wave and T-wave 

P-wave	T-wave
1. In an electrocardiogram (ECG), the P-wave indicates the activation of the SA node.	1. In an electrocardiogram (ECG), the T-wave represents ventricular relaxation.
2. During this phase, the impulse of contraction is generated by the SA node, causing atrial depolarization.	2. During this phase, the ventricles relax and return to their normal state
3. It is of atrial origin.	3. It is of ventricular origin.

Q8. Describe the evolutionary change in the pattern of the heart among the vertebrates.

Answer: All vertebrates possess a heart – a hollow muscular organ composed of cardiac muscle fibers. The function of the heart is to pump oxygen to all parts of the body. The evolution of the heart is based on the separation of oxygenated blood from deoxygenated blood for efficient oxygen transport. In fishes, the heart was like a hollow tube. This evolved into the four-chambered heart in mammals.
Piscean heart:
Fish has only two chambers in its heart – one auricle and one ventricle. Since both the auricle and the ventricle remain undivided, only deoxygenated blood passes through it. The deoxygenated blood enters the gills for oxygenation from the ventricle. It has additional chambers such as sinus venosus and conus arteriosus.

Amphibian heart: 
Amphibians, such as frogs, have three-chambered hearts, with two auricles and one ventricle. The auricle is divided into a right and a left chamber by an interauricular septum, while the ventricle remains undivided.
Additional chambers such as sinus venosus and conus arteriosus are also present. The oxygenated blood from the lungs enters the left auricle and simultaneously, the deoxygenated blood from the body enters the right auricle. Both these auricles empty into the ventricle, wherein the oxygenated and deoxygenated blood gets mixed to some extent.

Reptilian heart:
Reptiles have incomplete four-chambered hearts, except for crocodiles, alligators, and gharials. They have only one accessory chamber called the sinus venosus. The reptilian heart also shows mixed-blood circulation.

Avian and mammalian hearts: 
They have two pairs of chambers for separating oxygenated and deoxygenated blood. The heart is divided into four chambers. The upper two chambers are called atria and the lower two chambers are called ventricles. The chambers are separated by a muscular wall that prevents the mixing of the blood rich in oxygen with the blood rich in carbon dioxide.

Q9. Why do we call our heart myogenic?

Answer: In the human heart, contraction is initiated by a specially modified heart muscle known as sino-atrial node. It is located in the right atrium. The SA node has the inherent power of generating a wave of contraction and controlling the heartbeat. Hence, it is known as the pacemaker. Since the heartbeat is initiated by the SA node and the impulse of contraction originates in the heart itself, the human heart is termed myogenic. The hearts of vertebrates and mollusks are also myogenic.

Q10. Sino-atrial node is called the pacemaker of our heart. Why?

Answer: The sino-atrial (SA) node is a specialized bundle of neurons located in the upper part of the right atrium of the heart. The cardiac impulse originating from the SA node triggers a sequence of electrical events in the heart, thereby controlling the sequence of musclecontraction that pumps blood out of the heart. Since the SA node initiates and maintains the rhythmicity of the heart, it is known as the natural pacemaker of the human body.

Q11. What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?

Answer: The atrioventricular (AV) node is present in the right atrium, near the base of the interauricular septum that separates the right auricle from the ventricle. It gives rise to the bundle of His that conducts the cardiac impulses from the auricles to the ventricles. As the bundle of His passes the ventricle along the interventricular septum, it divides into two branches – the right ventricle and the left ventricle. The end branches of this conducting system then form a network of Purkinje fibers that penetrate into the myocardium. The auricular contraction initiated by the wave of excitation from the sinoatrial node (SA node) stimulates the atrioventricular node, thereby leading to the contraction of ventricles through the bundle of His and Purkinje fibers. Hence, the atrioventricular node and the atrioventricular bundle play a role in the contraction of ventricles.

Q12. Define a cardiac cycle and the cardiac output.

Answer: Cardiac cycle is defined as the complete cycle of events in the heart from the beginning of one heartbeat to the beginning of the next. It comprises three stages – atrial systole, ventricular systole, and complete cardiac diastole. Cardiac output is defined as the amount of blood pumped out by the ventricles in a minute.

Q13. Explain heart sounds.

Answer: Heart sounds are noises generated by the closing and opening of the heart valves. In a healthy individual, there are two normal heart sounds called lub and dub. Lub is the first heart sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of the systole. The second heart sound dub is associated with the closure of the semilunar valves at the beginning of the diastole. These sounds provide important information about the condition and working of the heart.

Q14. Draw a standard ECG and explain the different segments in it.

Answer: Electrocardiogram is a graphical representation of the cardiac cycle produced by an electrograph. The diagrammatic representation of a standard ECG is shown below.

A typical human electrocardiogram has five waves – P, Q, R, S, and T. The P, R, and T-waves are above the baseline and are known as positive waves. The Q and S waves are
below the baseline and are known as negative waves. The P-wave is of atrial origin, while the Q, R, S, and T-waves are of ventricular origin.
(a) The P-wave indicates atrial depolarization. During this wave, the impulse of contraction is generated by the SA node. The PQ-wave represents atrial contraction.
(b) The QR-wave is preceded by ventricular contraction. It represents the spread of the impulse of contraction from the AV node to the wall of the ventricle. It leads to ventricular depolarization.
(c) The RS-wave represents the ventricular contraction of about \(0.3 \mathrm{sec}\).
(d) The ST-wave represents ventricular relaxation of about \(0.4 \mathrm{sec}\). During this phase, the ventricles relax and return to their normal state.
(e) The T-wave represents ventricular relaxation.

Exemplar Section

VERY SHORT ANSWER TYPE QUESTIONS

Q1. Name the blood component which is viscous and straw coloured fluid.

Answer: Plasma 

Q2. Complete the missing word in the statement given below:
a. Plasma without _________ factors is called serum.
b. ___________ and monocytes are phagocytic cells.
c. Eosinophils are associated with _____ reactions.
d. _______ ions play a significant role in clotting.
e. One can determine the heart beat rate by counting the number of _________ in an ECG.

Answer: a. Plasma without clotting factors is called serum.
b. Neutrophils and monocytes are phagocytic cells.
c. Eosinophils are associated with allergic reactions.
d. Calcium ions play a significant role in clotting.
e. One can determine the heart beat rate by counting the number of QRS complex in an ECG.

Q3. Given below is the diagrammatic representation of a standard ECG. Label its different peaks.

Answer: 

Q4. Name the vascular connection that exists between the digestive tract and liver.

Answer: Hepatic portal system

Q5. Given below are the abnormal conditions related to blood circulation. Name the disorders.
a. Acute chest pain due to failure of \(\mathrm{O}_2\) supply to heart muscles
b. Increased systolic pressure

Answer: a. Acute chest pain due to failure of \(\mathrm{O}_2\) supply to heart muscles-Angina
b. Increased systolic pressure-Hypertension/high blood pressure

Q6. Which coronary artery diseases is caused due to narrowing of the lumen of arteries?

Answer: Atherosclerosis

Q7. Define the following terms and give their location?
a. Purkinje fibre
b. Bundle of His

Answer:  a. Purkinje fibre-Right and left bundles give rise to minute fibres throughout the ventricular musculature of the respective sides and are called purkinje fibres. .
b. Bundle of His-Purkinje fibres alongwith right and left bundles are known as bundle of His and present in ventricles.

Q8. State the functions of the following in blood
a. Fibrinogen
b. Globulin
c. Neutrophils
d. Lymphocytes

Answer: a. Fibrinogen—Fibrinogens are needed for clotting or coagulation of blood. 
b. Globulin—Globulins primarily are involved in immunity, i.e., defense mechanisms of the body.
c. Neutrophils—Phagocytosis
d. Lymphocytes—Immunity

Q9. What physiological circumstances lead to erythroblastosis foetalis?

Answer: A special case of Rh incompatibility (mismatching) has been observed between the Rh-negative blood of a pregnant mother with Rh-positive blood of the foetus.

Q10. Explain the consequences of a situation in which blood does not coagulate.

Answer: This situation leads to excessive loss of blood from body due to injury which can be fatal.

Q11. What is the significance of time gap in the passage of action potential from sino-atrial node to the ventricle?

Answer: This time gap is significant for ventricular systole.

Q12. How will you interpret an electrocardiogram (ECG) in which time taken in QRS complex is higher.

Answer: Period of ventricular systole increases.

SHORT ANSWER TYPE QUESTIONS

Q1. The walls of ventricles are much thicker than atria. Explain.

Answer: The walls of ventricles are much thicker than atria because they pump blood more strongly than the atria.

Q2. Differentiate between
a. Blood and Lymph
b. Basophils and Eosinophils
c. Tricuspid and bicuspid valve

Answer: a. Blood and Lymph: Blood is a connective tissue consisting of a fluid matrix, plasma and formed elements (RBCs, WBCs and Platelets). Blood flows in blood vascular system comprising heart, arteries and veins. Lymph is a colourless fluid containing specialised lymphocytes (imparting immunity to the body), but devoid of RBCs. Lymph flows in the lymphatic system and it absorbs fats.

\(
\begin{array}{|l|l|l|l|}
\hline \text { a. } & \text { Blood } & & \text { Lymph } \\
\hline \text { 1. } & \begin{array}{l}
\text { It contains plasma, RBCs, WBCs and } \\
\text { platelets }
\end{array} & 1 . & \text { It contains plasma and lymphocytes } \\
\hline \text { 2. } & \text { It is red in colour } & 2 . & \text { It is colourless } \\
\hline \text { 3. } & \text { Haemoglobin is present } & 3 . & \text { Haemoglobin is absent } \\
\hline \text { 4. } & \begin{array}{l}
\text { It transports nutrients and gases from } \\
\text { heart to tissues and vice-versa }
\end{array} & \text { 4. } & \begin{array}{l}
\text { It transports infection fighting white blood } \\
\text { cells from tissues to lymph nodes }
\end{array} \\
\hline
\end{array}
\) \(
\begin{array}{|l|l|l|l|}
\hline \text { b. } & \text { Basophils } & & \text { Eosinophils } \\
\hline \text { 1. } & \text { They constitute about } 0.5-1 \% \text { of WBCs } & 1 . & \text { They constitute about 2-3% of WBCs } \\
\hline \text { 2. } & \text { They secrete heparin, } & & \\
& \text { histamine and serotonin } & 2 . & \text { They resist infection } \\
\hline \text { 3. } & \begin{array}{l}
\text { They are involved in inflammatory } \\
\text { reaction }
\end{array} & 3 . & \text { These are associated with allergic reactions } \\
\hline
\end{array}
\) \(
\begin{array}{|l|l|l|l|}
\hline \text { c. } & \text { Tricuspid valve } & & \text { Bicuspid valve } \\
\hline \text { 1. } & \text { It has three cusps. } & 1 . & \text { It have two cusps. } \\
\hline \text { 2. } & \begin{array}{l}
\text { It is present between right atrium and } \\
\text { right ventricle }
\end{array} & 2 . & \begin{array}{l}
\text { It is present between left atrium and left } \\
\text { ventricle. }
\end{array} \\
\hline
\end{array}
\)

Q3. Briefly describe the followings:
a. Anaemia
b. Angina Pectoris
c. Atherosclerosis
d. Hypertension
e. Heart failure
f. Erythroblastosis foetalis

Answer: a. Anaemia: Decrease in oxygen carrying capacity of blood either due to reduced RBCs production or low haemoglobin content is called anaemia.
b. Angina Pectoris: A symptom of acute chest pain appears when no enough oxygen is reaching the heart muscle. Angina can occur in men and women of any age but it is more common among the middle-aged ” and elderly. It occurs due to conditions that affect the blood flow.
c. Atherosclerosis: Sometimes deposition of calcium, fat, cholesterol and fibrous tissues occurs in the blood vessel (e.g., coronary artery) supplying blood to the heart muscles. This condition makes the lumen of arteries narrower affecting blood supply to heart; which leads to Coronary Artery Disease (CAD) also referred to as atherosclerosis.
d. Hypertension: If repeated checks of blood pressure of an individual is 140/90 (140 over 90) or higher, it shows hypertension. High blood pressure leads to heart diseases and also affects vital organs like brain and kidney.
e. Heart failure: Heart failure means the state of heart when it is not pumping blood effectively enough to meet the needs of the body. It is sometimes called congestive heart failure because congestion of the lungs is one of the main symptoms of this disease.
f. Erythroblastosis foetalis: A special case of Rh incompatibility (mismatching) has been observed between the Rh-negative blood of a pregnant mother with Rh-positive blood of the foetus! Rh antigens of the foetus do not get exposed to the Rh-negative blood of the mother in the first pregnancy as the two bloods are well separated by the placenta. However, during the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of the Rh-positive blood from the foetus. In such cases, the mother starts preparing antibodies against Rh antigen in her blood. In case of her subsequent pregnancies, the Rh antibodies from the mother (Rh-negative) can leak into the blood of the foetus (Rh-positive) and destroy the foetal RBCs. This could be fatal to the foetus or could cause severe anaemia and jaundice to the baby. This condition is called erythroblastosis foetalis. This can be avoided by administering anti-Rh antibodies to the mother immediately after the delivery of the first child.

Q4. Explain the advantage of the complete partition of ventricle among birds and mammals and hence leading to double circulation.

Answer: Complete partition of ventricle among birds and mammals is advantageous because there is no mixing of oxygenated and deoxygenated blood in the ventricle, so tissues of the body receive more oxygenated blood.

Q5. What is the significance of hepatic portal system in the circulatory system?

Answer: The hepatic portal vein carries blood from intestine to liver before it is delivered to systemic circulation. This is significant because excess of nutrients like glucose is converted into glycogen in liver and stored there.

Q6. Explain the functional significance of lymphatic system?

Answer: As the blood passes through the capillaries in tissues, some water along with many small water soluble substances move out into the spaces between the cells of tissues leaving the larger proteins and most of the formed elements in the blood vessels. This fluid released out is called the interstitial fluid or tissue fluid. It has the same mineral distribution as that in plasma. Exchange of nutrients, gases, etc., between the blood and the cells always occur through this, fluid. An elaborate network of vessels called the lymphatic system collects this fluid and drains it back to the major veins. The fluid present in the lymphatic system is called the lymph. Lymph is a colourless fluid containing specialised lymphocytes which are responsible for the immune responses of the body. Lymph is also an important carrier for nutrients, hormones, etc. Fats are absorbed through lymph in the lacteals present in the intestinal villi.

Q7. Write the features that distinguish between the two
a. Plasma and Serum
b. Open and closed circulatory system
c. Sino-atrial node and Atrio-ventricular node

Answer: 

\(
\begin{array}{|l|l|l|l|}
\hline \text { a. } & \text { Plasma } & & \text { Serum } \\
\hline \text { i. } & \text { Blood without formed } & & \\
& \text { elements is called plasma } & 1 . & \begin{array}{l}
\text { Plasma without clotting factor is called } \\
\text { serum }
\end{array} \\
\hline \text { 2. } & \text { Plasma has clotting factors } & 2 . & \text { Serum does not have clotting factors } \\
\hline \text { 3. } & \text { Plasma involved in blood coagulation } & 3 . & \begin{array}{l}
\text { Serum does not involve in blood } \\
\text { coagulation }
\end{array} \\
\hline
\end{array}
\) \(
\begin{array}{|l|l|l|l|}
\hline \text { b. } & \text { Open circulatory system } & & \text { Closed circulatory system } \\
\hline \text { 1. } & \begin{array}{l}
\text { Blood pumped by heart passes through } \\
\text { large vessels into open spaces or body } \\
\text { cavities called sinuses }
\end{array} & \text { 1. } & \begin{array}{l}
\text { Blood pumped by the heart is always } \\
\text { circulated through a closed network of } \\
\text { blood vessels }
\end{array} \\
\hline 2 . & \text { Less advantageous } & \text { 2. } & \text { More advantageous } \\
\hline \text { 3. } & \begin{array}{l}
\text { Flow of fluid cannot be more precisely } \\
\text { regulated }
\end{array} & \text { 3. } & \begin{array}{l}
\text { Flow of fluid can be more precisely } \\
\text { regulated }
\end{array} \\
\hline 4 . & \begin{array}{l}
\text { It is present in arthropods molluscs, and } \\
\text { hemichordates }
\end{array} & 4 . & \text { It is found in annelids and chordates } \\
\hline
\end{array}
\)

\(
\begin{array}{|l|l|l|l|}
\hline \text { c. } & \text { Sino-atrial node } & & \text { Atrio-ventricular node } \\
\hline \text { 1. } & \begin{array}{l}
\text { SA node is present in the right upper } \\
\text { comer of the right atrium }
\end{array} & \text { 1. } & \begin{array}{l}
\text { AV node is present in the lower left comer } \\
\text { of the right atrium }
\end{array} \\
\hline \text { 2. } & \begin{array}{l}
\text { It initiates and maintains the rhythmic } \\
\text { contractile activity of the heart }
\end{array} & \text { 2. } & \begin{array}{l}
\text { It passes the electrical impulses from SA } \\
\text { node to AV bundle }
\end{array} \\
\hline \text { 3. } & \text { It is also called pace-maker } & \text { 3. } & \text { It is also called pace-setter } \\
\hline
\end{array}
\)

Q8. Thrombocytes are essential for coagulation of blood. Comment.

Answer: Introduction of thrombocytes:

• Thrombocytes are also called blood platelets and are corpuscles that circulate within the blood with a life span of about 10 days.
• When the endothelial lining of a blood vessel is injured, platelets in large numbers immediately attach to the injured surface and to each other, forming an adherent mass of platelets.
• They are the first cells to reach the site of injury and initiate the process of blood clotting.

Function of thrombocytes:

• The effect of the platelet response is to stop the bleeding and to form the site of the developing blood clot, or thrombus.
• If platelets are absent, this important defense reaction cannot occur, and prolonged bleeding from small wounds will occur.
• Platelets also contribute substances essential for the normal coagulation of the blood, and they cause the shrinking, or retraction, of a clot after it has been formed.

Q9. Answer the following
a. Name the major site where RBCs are formed.
b. Which part of heart is responsible for initiating and maintaining its rhythmic activity?
c. What is specific in the heart of crocodiles among reptilians?

Answer: a. Bone marrow
b. Sino-Atrial Node (SA Node)
c. Reptiles have 3-chambered heart but crocodiles have 4-chambered heart.

LONG ANSWER TYPE QUESTIONS

Q1. Explain Rh-incompatibility in humans.

Answer: A special case of Rh-incompatibility (mismatching) has been observed between the Rh-negative blood of a pregnant mother with Rh-positive blood of the foetus. Rh antigens of the foetus do not get exposed to the Rh-negative blood of the mother in the first pregnancy as the two bloods are well separated by the placenta. However, during the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of the Rh – positive blood from the foetus. In such cases, the mother starts preparing antibodies against Rh antigen in her blood. In case of her subsequent pregnancies, the Rh antibodies from the mother (Rh-negative) can leak into the blood of the foetus (Rh-positive) and destroy the foetal RBCs. This could be fatal to the foetus or could cause severe anaemia and jaundice to the baby. This condition is called erythroblastosis foetalis. This can be avoided by administering anti-Rh antibodies to the mother immediately after the delivery of the first child.

Q2. Describe the events in cardiac cycle. Explain “double circulation”.

Answer: Cardiac cycle: To begin with, all the four chambers of heart are in a relaxed state, i.e., they are in joint diastole. As the tricuspid and bicuspid valves are open, blood from the pulmonary veins and vena cava flows into the left and the right ventricle respectively through the left and right atria. The semilunar valves are closed at this stage. The SAN now generates an action potential which stimulates both the atria to undergo a simultaneous contraction-the atrial systole. This increases the flow of blood into the ventricles by about 30\%. The action potential is conducted to the ventricular side by the AVN and AV bundle from where the bundle of His transmits it through the entire ventricular musculature. This causes the ventricular muscles to contract (ventricular systole), the atria undergoes relaxation (diastole), coinciding with the ventricular systole. Ventricular systole increases the ventricular pressure causing the closure of tricuspid and bicuspid valves due to attempted backflow of blood into the atria. As the ventricular pressure increases further, the semilunar valves guarding the pulmonary artery (right side) and the aorta (left side) are forced open, allowing the blood in the ventricles to flow through these vessels into the circulatory pathways. The ventricles now relax (ventricular diastole) and the ventricular pressure falls causing the closure of semilunar valves which prevents the backflow of blood into the ventricles. As the ventricular pressure declines further, the tricuspid and bicuspid valves are pushed open by the pressure in the atria exerted by the blood which was being emptied into them by the veins. The blood now once again moves freely to the ventricles. The ventricles and atria are now again in a relaxed (joint diastole) state, as earlier. Soon the SAN generates a new action potential and the events described above are repeated in that sequence and the process continues.

Double circulation: The blood pumped by the right ventricle enters the pulmonary artery, whereas the left ventricle pumps blood into the aorta. The deoxygenated blood pumped into the pulmonary artery is passed on to the lungs from where the oxygenated blood is carried by the pulmonary veins into the left atrium. This pathway constitutes the pulmonary circulation. The oxygenated blood entering the aorta is carried by a network of arteries, arterioles and capillaries to the tissues from where the deoxygenated blood is collected by a system of venules, veins and vena cava and emptied into the right atrium. This is the systemic circulation. The systemic circulation provides nutrients, \(O_2\) and other essential substances to the tissues and takes \(\mathrm{CO_2}\) and other harmful substances away for elimination.

Q3. Explain different types of blood groups and donor compatibility by making a table.

Answer: ABO blood grouping is based on the presence or absence of two surface antigens on the RBCs namely \(A\) and \(B\). Similarly, the plasma of different individuals contain two natural antibodies anti-A and antiB. Blood group ‘\(A\)‘ carries antigen-A and antibodies-B. The donor’s group for blood group \(A\) are \(A\) and \(O\). Blood group \(B\) carries antigen-B and antibodies-A. The donor’s group for blood group \(B\) are \(B\) and \(O\) . Blood group \(A B\) carries antigens \(A\) and \(B\) but no corresponding antibodies so, the compatible donor’s group for blood group \(A B\) are \(A, B, A B\) and \(O\) hence, blood group ‘ \(A B\) ‘ is also called as “universal acceptor”. Blood group ‘\(O\)‘ carries no antigens but carries antibodies both \(A\) and \(B\) hence its compatible donor’s group is only ‘ \(O\) ‘ but it is a compatible donor group for all the blood groups. \(A, B, A B\) and \(O\) hence, blood group ‘ \(O\) ‘ is called as ‘universal donor’.

Blood groups and donor compatibility
\(
\begin{array}{|l|l|l|l|}
\hline \text { Blood Group } & \text { Antigen on RBCs } & \text { Antibodies in Plasma } & \text { Donor’s Compatibility } \\
\hline \text { A } & \text { A } & \text { Anti-B } & \text { A, O } \\
\hline \text { B } & \text { B } & \text { Anti-A } & \text { B, } O \\
\hline \text { AB } & \text { A B } & \text { Nil } & \text { AB, A, B, O } \\
\hline \text { O } & \text { Nil } & \text { Anti – A, B } & 0 \\
\hline
\end{array}
\)

Q4. Write short note on the following
a. Hypertension
b. Coronary Artery Disease

Answer: a. Hypertension: If repeated checks of blood pressure of an individual is 140/90 (140 over 90) or higher, it shows hypertension. High blood pressure leads to heart diseases and also affects vital organs like brain and kidney.
b. Coronary Artery Disease: Coronary Artery Disease, often referred to as atherosclerosis, affects the vessels that supply blood to the heart muscle. It is caused by deposits of calcium, fat, cholesterol and fibrous tissues, which makes the lumen of arteries narrower.

Q5. In the diagrammatic presentation of heart given below, mark and label, SAN, AVN, AV bundles, bundle of His and Purkinje fibres.

Answer: