Question and Answer:

Question 1.
Name the components of the formed elements in the blood and mention one major function of each of them.
Answer:
Red blood cells (RBCs) or erythrocytes, white blood cells (WBCs) or leucocytes, and platelets are collectively called formed elements, and they constitute nearly 45% of the blood.

Major Functions:

• RBCs: Transport of gases (O₂ and CO₂).
• WBCs: Fight against infections and provide immunity.
• Platelets: Help in blood clotting and prevent excessive bleeding.

Question 2.
What is the importance of plasma proteins?
Answer:
Fibrinogen, globulins, and albumins are the major proteins found in plasma.

• Fibrinogen: Needed for the clotting of blood.
• Globulins: Involved in the defense mechanisms of the body.
• Albumins: Help in maintaining osmotic balance.

Question 3.
Match Column I with Column II:

                 Column I                               Column II

           (a) Eosinophils                         (i) Coagulation

           (b) RBC                                     (ii) Universal Recipient

           (c) AB Group                           (iii) Resist Infections

           (d) Platelets                            (iv) Contraction of Heart

           (e) Systole                               (v) Gas transport

Answer:
(a) → (iii)
(b) → (v)
(c) → (ii)
(d) → (i)
(e) → (iv)

Question 4.
Why do we consider blood as a connective tissue?
Answer:
Blood is considered a connective tissue because it connects different body systems by transporting materials such as oxygen, carbon dioxide, nutrients, hormones, and wastes. It also originates from mesoderm (like other connective tissues) and consists of living cells (formed elements) suspended in a non-living fluid matrix called plasma.

Question 5.
What is the difference between lymph and blood?
Answer:

Question 6.
What is meant by double circulation? What is its significance?
Answer:

Double circulation:
It is the passage of the same blood twice through the heart to complete one cycle.

• Pulmonary circulation: Deoxygenated blood is pumped from the heart to the lungs for oxygenation.
• Systemic circulation: Oxygenated blood returns to the heart and is then pumped to all parts of the body. Deoxygenated blood returns to the heart to be pumped to the lungs again.

Significance:

• Prevents the mixing of oxygenated and deoxygenated blood.
• Ensures that oxygenated blood carries more oxygen per unit volume, providing efficient oxygen supply for metabolism.
• Allows deoxygenated blood to carry more CO₂ for removal from the body.

Question 7.
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: Fluid connective tissue containing plasma, RBCs, WBCs, and platelets.
• Lymph: Tissue fluid formed from blood; contains lymphocytes but lacks RBCs and platelets.

(b) Open and Closed system of circulation

• Open circulatory system: Found in arthropods and mollusks; blood pumped by the heart flows into open spaces or sinuses.
• Closed circulatory system: Found in annelids and chordates; blood circulates only through a closed network of vessels. Flow can be better regulated in a closed system.

(c) Systole and Diastole

• Systole: Contraction of heart muscles; increases pressure in heart chambers.
• Diastole: Relaxation (dilation) of heart muscles; decreases pressure in heart chambers.

(d) P-wave and T-wave (ECG)

• P-wave: Electrical excitation (depolarisation) of atria; leads to atrial contraction.
• T-wave: Repolarisation of ventricles; marks the end of ventricular systole.

Question 8.
Describe the evolutionary change in the pattern of heart among the vertebrates.
Answer:
All vertebrates possess a muscular chambered heart.

• Fishes: Have a 2-chambered heart (1 atrium + 1 ventricle) and exhibit single circulation, where deoxygenated blood is pumped to the gills for oxygenation and then supplied to the body.
• Amphibians and Reptiles: Have a 3-chambered heart (2 atria + 1 ventricle) and exhibit incomplete double circulation, where oxygenated and deoxygenated blood mix in the single ventricle.
• Crocodiles, Birds, and Mammals: Have a 4-chambered heart (2 atria + 2 ventricles) with complete double circulation, where oxygenated and deoxygenated blood are completely separated, ensuring efficient supply of oxygen to the body.

This evolutionary change allows vertebrates to meet increasing metabolic demands.

Question 9.
Why do we call our heart myogenic?
Answer:
The heart is called myogenic because its rhythmic contractions are initiated by the cardiac muscles themselves, without requiring any external nervous stimulation. Specialized cardiac muscle tissue, called nodal tissue, generates action potentials spontaneously. The sino-atrial node (SAN) acts as the pacemaker, controlling the rate and rhythm of the heartbeat.

Question 10.
Sino-atrial node is called the pacemaker of our heart. Why?
Answer:
The sino-atrial node (SAN) is called the pacemaker because it generates the maximum number of action potentials per minute (70–75/min), which initiates and maintains the rhythmic contraction of the heart. These impulses from the SAN spread to the atria and then to the ventricles, setting the pace of the heartbeat.

Question 11.
What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?
Answer:
The atrioventricular node (AVN) is a mass of specialized neuro-muscular tissue located in the wall of the right atrium. It receives the wave of contraction initiated by the sino-atrial node (SAN) and delays it briefly to allow the atria to empty completely into the ventricles.

The Bundle of His is a bundle of specialized fibers that originates from the AVN. Along with the Purkinje fibers, it forms the atrioventricular bundle, which conveys the impulses from the AV node to the ventricular muscles, ensuring coordinated contraction of the ventricles.

Question 12.
Define a cardiac cycle and the cardiac output.
Answer:

• Cardiac Cycle: The sequential events from the beginning of one heartbeat to the beginning of the next, which are cyclically repeated, are called the cardiac cycle.
• Cardiac Output: The volume of blood pumped by each ventricle per minute is called the cardiac output. In a healthy individual, it is approximately 5000 mL (5 litres) per minute.

Question 13.
Explain heart sounds.
Answer:
The rhythmic closing and opening of the heart valves produces the sounds of the heartbeat:

• First heart sound (Lub): Lasts about 0.16–0.19 seconds and is caused by the closure of the atrioventricular valves (tricuspid and bicuspid/mitral valves) at the beginning of ventricular systole.
• Second heart sound (Dub): Lasts about 0.10 seconds and is caused by the closure of the semilunar valves (aortic and pulmonary valves) at the beginning of ventricular diastole.

These sounds are clinically important for detecting valve function and heart abnormalities.

Question 14.
Draw a standard ECG and explain the different segments in it.
Answer: