Exercises
Name the components of the formed elements in the blood and mention one major function of each of them.
Answer
The formed elements in blood are:
Red Blood Cells (RBCs / Erythrocytes): Transport O2 from lungs to tissues and CO2 from tissues to lungs, via haemoglobin.
White Blood Cells (WBCs / Leukocytes): Defence against infections (immunity). Subtypes include neutrophils, eosinophils, basophils, monocytes, and lymphocytes.
Platelets (Thrombocytes): Play a key role in blood clotting (haemostasis) by forming a platelet plug at the site of injury and releasing clotting factors.
What is the importance of plasma proteins?
Answer
Plasma proteins (albumins, globulins, fibrinogen) serve multiple important functions: (i) Albumin — maintains colloidal osmotic pressure of blood, preventing fluid leakage into tissues (oedema); transports fatty acids, hormones, and drugs. (ii) Globulins (immunoglobulins) — function as antibodies, providing immunity against pathogens. (iii) Fibrinogen — converted to fibrin during blood clotting, forming the clot. (iv) All plasma proteins — contribute to blood viscosity, pH buffering, and transport of various molecules.
Match Column I with Column II
Answer
(a) Eosinophils — (iii) Resist Infections (eosinophils combat parasitic infections and allergic reactions)
(b) RBC — (v) Gas transport
(c) AB Group — (ii) Universal Recipient
(d) Platelets — (i) Coagulation
(e) Systole — (iv) Contraction of Heart
Why do we consider blood as a connective tissue?
Answer
Blood is classified as a specialised connective tissue because: (i) It has cells (formed elements — RBCs, WBCs, platelets) scattered in a fluid matrix (plasma), just as connective tissues have cells in a matrix. (ii) It develops from mesenchyme (mesodermal origin), the same embryonic tissue that gives rise to other connective tissues. (iii) It connects and integrates all organs by transporting nutrients, hormones, gases, and waste products throughout the body, maintaining homeostasis — a connective function.
What is the difference between lymph and blood?
Answer
Blood is a red-coloured fluid containing plasma + RBCs + WBCs + platelets. It flows through arteries, veins, and capillaries in a closed system under pressure; it carries O2, nutrients, hormones, and waste. Lymph is a colourless/pale fluid (no RBCs, fewer proteins, no platelets) derived from the tissue fluid that enters lymphatic capillaries; it flows through lymphatic vessels (a one-way system) driven by muscle contractions and skeletal movement. Lymph contains lymphocytes and returns excess interstitial fluid, proteins, and absorbed fats (chyle) back to the blood. It plays a crucial role in immunity.
What is meant by double circulation? What is its significance?
Answer
In double circulation, blood passes through the heart twice in each complete circuit of the body: once through the pulmonary circuit (right heart
⇒ lungs
⇒ left heart) to be oxygenated, and once through the systemic circuit (left heart
⇒ body
⇒ right heart) to deliver O2 to tissues. Significance: (i) It keeps oxygenated and deoxygenated blood completely separated, ensuring tissues always receive fully oxygenated blood. (ii) It allows higher blood pressure to be maintained in the systemic circuit, enabling efficient nutrient and gas delivery to all tissues. (iii) It supports the high metabolic rates of warm-blooded vertebrates (mammals and birds).
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 vs Lymph: Blood has RBCs, WBCs, platelets, and plasma proteins in high concentration; it is red-coloured and circulates in a closed system under pressure. Lymph lacks RBCs and has fewer plasma proteins; it is colourless and flows in a one-way open lymphatic system. (See Q5 for more detail.)
(b) Open vs Closed circulation: In an open system (arthropods, most molluscs), blood (haemolymph) is pumped from the heart into open sinuses (haemocoels) where it bathes organs directly before returning to the heart; blood pressure is low. In a closed system (annelids, vertebrates), blood flows within a continuous system of vessels (arteries, capillaries, veins); blood pressure is higher and circulation is more efficient and controlled.
(c) Systole is the contraction phase of the heart; ventricular systole pumps blood into the aorta and pulmonary artery. Diastole is the relaxation phase; chambers fill with blood. Systole raises blood pressure; diastole allows refilling.
(d) The P-wave in an ECG represents the depolarisation (electrical excitation) of the atria, just before atrial contraction. The T-wave represents ventricular repolarisation (recovery/relaxation of the ventricles after contraction). The QRS complex between them represents ventricular depolarisation.
Describe the evolutionary change in the pattern of heart among the vertebrates.
Answer
The vertebrate heart shows a clear evolutionary progression in complexity:
Fish: Two-chambered heart (one atrium + one ventricle); single circulation; deoxygenated blood from body
⇒ heart
⇒ gills (for oxygenation)
⇒ body.
Amphibians: Three-chambered heart (two atria + one ventricle); incomplete double circulation; some mixing of oxygenated and deoxygenated blood in the single ventricle.
Reptiles (except crocodiles): Three-chambered heart with a partial ventricular septum, reducing mixing slightly; crocodiles have a four-chambered heart.
Birds and Mammals: Four-chambered heart (two atria + two ventricles, completely separated); complete double circulation; oxygenated and deoxygenated blood kept entirely separate, allowing highest metabolic rates.
Why do we call our heart myogenic?
Answer
The mammalian heart is called myogenic because the impulse for cardiac contraction originates from specialised cardiac muscle cells themselves (the sino-atrial node, SA node) rather than from nerve fibres. The SA node spontaneously generates rhythmic electrical impulses. This intrinsic pacemaker activity of cardiac muscle fibres means the heart can beat without any external neural input, though the rate is modulated by the autonomic nervous system.
Sino-atrial node is called the pacemaker of our heart. Why?
Answer
The sino-atrial (SA) node, located in the right atrial wall near the opening of the superior vena cava, is called the pacemaker because it spontaneously generates electrical impulses at the highest inherent rate (~70–80 times/min) among all cardiac pacemaker cells. Its impulse sets the pace for the entire heart — each impulse initiates a wave of excitation that spreads across both atria (causing atrial contraction), reaches the AV node, and then the ventricles, coordinating the heartbeat. Because it initiates and controls the normal heart rate, it is the pacemaker.
What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?
Answer
The AV node (atrio-ventricular node) at the base of the right atrium delays the electrical impulse from the atria for ~0.1 seconds before passing it to the ventricles. This delay ensures that the atria finish contracting and emptying blood into the ventricles before ventricular contraction begins, coordinating the pumping sequence. The AV bundle (Bundle of His) conducts the impulse rapidly from the AV node down the interventricular septum via the bundle branches (Purkinje fibres) to the ventricular muscle, ensuring both ventricles contract simultaneously and from the apex upward for efficient ejection of blood.
Define a cardiac cycle and the cardiac output.
Answer
The cardiac cycle is the complete sequence of events — from the beginning of one heartbeat to the beginning of the next — comprising atrial systole, ventricular systole, and cardiac diastole (joint relaxation). It lasts approximately 0.8 seconds at rest (heart rate 75 beats/min).
Cardiac output is the volume of blood pumped by one ventricle per minute: Cardiac Output = Stroke Volume × Heart Rate. At rest: ≈ 70 mL × 72 beats/min ≈ 5000 mL/min (5 L/min). It increases significantly during exercise.
Explain heart sounds.
Answer
Two main heart sounds are produced during each cardiac cycle:
"Lubb" (S1): Produced by the closure of the tricuspid (right AV) and bicuspid/mitral (left AV) valves at the beginning of ventricular systole. It is a longer, lower-pitched sound.
"Dupp" (S2): Produced by the closure of the semilunar valves (aortic and pulmonary) at the beginning of ventricular diastole. It is a shorter, sharper sound.
These sounds indicate proper valve function. Abnormal sounds (murmurs) suggest valve defects such as stenosis (narrowing) or regurgitation (backflow).
Draw a standard ECG and explain the different segments in it.
Answer
An ECG (electrocardiogram) records the electrical activity of the heart. The standard ECG shows:
P-wave: Small upward deflection representing depolarisation (electrical excitation) of the atria; atrial contraction follows.
QRS complex: A sharp deflection representing ventricular depolarisation (ventricles receive electrical stimulus); ventricular contraction begins. Q is a small downward deflection, R is a tall upward peak, S is a downward deflection.
T-wave: Broader upward deflection representing ventricular repolarisation (electrical recovery of ventricles); ventricular relaxation.
P-R interval: Time between atrial and ventricular depolarisation (includes AV nodal delay).
S-T segment: Period between end of ventricular depolarisation and start of repolarisation; elevated or depressed in heart disease.
(Note: Students should draw the waveform showing P, Q, R, S, T in sequence.)
Important Extra Questions
What is the ABO blood grouping system?
Answer
The ABO system classifies blood into four groups based on antigens (agglutinogens) on RBC surfaces and antibodies (agglutinins) in plasma. Group A: A antigen, anti-B antibody; Group B: B antigen, anti-A antibody; Group AB: both antigens, no antibodies (universal recipient); Group O: no antigens, both anti-A and anti-B antibodies (universal donor for packed RBCs). Mismatched transfusion causes agglutination and haemolysis.
What is the lymphatic system and its role in immunity?
Answer
The lymphatic system is a network of lymphatic capillaries, vessels, lymph nodes, and organs (thymus, spleen, tonsils). It drains excess interstitial fluid (as lymph) back to the bloodstream, absorbs dietary fats from the intestine as chyle, and crucially, is the site of immune responses: lymph nodes filter lymph, trap pathogens, and house lymphocytes that produce antibodies and cell-mediated responses.
What is the Frank-Starling law of the heart?
Answer
The Frank-Starling law states that the force of ventricular contraction (and hence stroke volume) is directly proportional to the initial length of the cardiac muscle fibres at the end of diastole (end-diastolic volume). The more the ventricle is filled with blood (stretched), the more forcefully it contracts to eject that blood. This intrinsic mechanism allows the heart to automatically match cardiac output to venous return.
What is hypertension and what are its consequences?
Answer
Hypertension (high blood pressure) is a sustained elevation of systolic blood pressure above 140 mmHg and/or diastolic above 90 mmHg. Consequences include: increased risk of stroke (cerebral haemorrhage), heart attack (myocardial infarction), heart failure (cardiac hypertrophy), kidney damage (nephrosclerosis), and retinal damage. It is often called the "silent killer" as it may have no symptoms until serious complications arise.
Distinguish between arteries and veins.
Answer
Arteries carry blood away from the heart (usually oxygenated, except pulmonary artery); have thick, elastic, muscular walls; carry blood under high pressure; and have no valves (except the semilunar valves at their origin). Veins carry blood toward the heart (usually deoxygenated, except pulmonary veins); have thin walls and a wider lumen; carry blood under low pressure; and possess valves to prevent backflow.