Chapter 18: Body Fluids and Circulation – MCQs
🩺 Body Fluids & Circulation – MCQs
Part 1 — Questions 1–25
Q1. The largest fluid compartment (by volume) in the adult human body is:
a) Plasma
b) Interstitial fluid
c) Intracellular fluid
d) Lymph
Answer: c) Intracellular fluid
Explanations:
- a) Plasma ≈ 3–4 L — much smaller than ICF.
- b) Interstitial fluid ≈ 10–11 L — the major part of ECF but still smaller than ICF.
- c) Intracellular fluid (ICF) ≈ 25–28 L in a 70 kg adult — largest compartment. ✅
- d) Lymph is a small fraction of ECF and not the largest compartment.
Q2. The main plasma protein responsible for maintaining colloid (oncotic) pressure is:
a) Fibrinogen
b) Globulins
c) Albumin
d) Hemoglobin
Answer: c) Albumin
Explanations:
- a) Fibrinogen — clotting protein; minor contribution to oncotic pressure.
- b) Globulins — contribute to oncotic pressure and immunity but less than albumin.
- c) Albumin — most abundant plasma protein; primary contributor to plasma oncotic pressure. ✅
- d) Hemoglobin — intracellular in RBCs; not a plasma protein.
Q3. Starling forces govern fluid exchange across capillary walls. Which force favors filtration from capillary into interstitium?
a) Plasma oncotic pressure (πp)
b) Interstitial hydrostatic pressure (Pi)
c) Capillary hydrostatic pressure (Pc)
d) Lymphatic pressure
Answer: c) Capillary hydrostatic pressure (Pc)
Explanations:
- a) Plasma oncotic pressure (πp) opposes filtration by pulling fluid into capillary.
- b) Interstitial hydrostatic pressure (Pi) opposes filtration (if positive).
- c) Capillary hydrostatic pressure (Pc) pushes fluid out of capillary → favors filtration. ✅
- d) Lymphatic pressure removes interstitial fluid but is not a primary Starling force favoring filtration.
Q4. Which of the following best describes hematocrit?
a) Percentage of plasma in whole blood
b) Volume percent of red blood cells in whole blood
c) Concentration of hemoglobin per 100 mL plasma
d) Number of RBCs per microliter
Answer: b) Volume percent of red blood cells in whole blood
Explanations:
- a) Plasma percentage = 100% − hematocrit; not the hematocrit itself.
- b) Correct — hematocrit (packed cell volume) = % of blood volume occupied by RBCs. ✅
- c) Hemoglobin concentration is measured separately (g/dL).
- d) RBC count is a number, not the hematocrit percentage.
Q5. Erythropoietin (EPO) is primarily produced by which organ in adults?
a) Liver
b) Spleen
c) Kidney (peritubular interstitial cells)
d) Bone marrow
Answer: c) Kidney (peritubular interstitial cells)
Explanations:
- a) Liver produces some EPO in fetus/under some conditions, but not primary in adults.
- b) Spleen stores and removes RBCs but does not majorly produce EPO.
- c) Kidney peritubular fibroblasts are the main source of EPO in adults — correct. ✅
- d) Bone marrow responds to EPO but does not secrete it.
Q6. Which blood vessel layer contains smooth muscle and is primarily responsible for vasoconstriction/vasodilation?
a) Tunica intima (intima)
b) Tunica media (media)
c) Tunica externa (adventitia)
d) Endothelium only
Answer: b) Tunica media (media)
Explanations:
- a) Tunica intima includes endothelium and subendothelial connective tissue.
- b) Tunica media contains smooth muscle and elastic tissue — primary site of vasomotor tone. ✅
- c) Tunica externa is connective tissue for support.
- d) Endothelium is part of intima; not the muscular layer.
Q7. The primary driving force for venous return to the heart during normal quiet breathing is:
a) Positive intrathoracic pressure during inspiration
b) Decreased thoracic pressure (subatmospheric) during inspiration
c) Left ventricular contraction only
d) Atrial fibrillation
Answer: b) Decreased thoracic pressure (subatmospheric) during inspiration
Explanations:
- a) Inspiration produces more negative (not positive) intrathoracic pressure.
- b) Correct — negative intrathoracic pressure during inspiration draws venous blood into thorax and increases venous return. ✅
- c) LV contraction moves blood forward but venous return is enhanced by thoracic pressure changes.
- d) Atrial fibrillation impairs effective filling; not a normal driver.
Q8. Which statement about lymph is TRUE?
a) Lymph originates only from plasma filtered by kidneys
b) Lymph flow is independent of skeletal muscle activity
c) Lymph returns excess interstitial fluid and proteins to the circulation via thoracic duct/right lymphatic duct
d) Lymph contains no immune cells
Answer: c) Lymph returns excess interstitial fluid and proteins to the circulation via thoracic duct/right lymphatic duct
Explanations:
- a) Lymph originates from interstitial fluid, not renal filtration alone.
- b) Lymph flow is aided by skeletal muscle pumps and one-way valves — not independent.
- c) Correct — lymph transports excess interstitial fluid/proteins and immune cells back into venous circulation via lymphatic trunks (thoracic duct/right lymphatic duct). ✅
- d) Lymph often contains lymphocytes and antigen-presenting cells.
Q9. Which heart chamber pumps oxygenated blood into systemic circulation?
a) Right atrium
b) Right ventricle
c) Left atrium
d) Left ventricle
Answer: d) Left ventricle
Explanations:
- a) Right atrium receives deoxygenated venous blood.
- b) Right ventricle pumps deoxygenated blood to the lungs (pulmonary circulation).
- c) Left atrium receives oxygenated blood from pulmonary veins.
- d) Left ventricle pumps oxygenated blood into the aorta for systemic circulation — correct. ✅
Q10. Which valve prevents backflow from the left ventricle into the left atrium?
a) Tricuspid valve
b) Mitral (bicuspid) valve
c) Pulmonary valve
d) Aortic valve
Answer: b) Mitral (bicuspid) valve
Explanations:
- a) Tricuspid is between right atrium & right ventricle.
- b) Mitral valve lies between left atrium & left ventricle — prevents regurgitation into LA during systole. ✅
- c) Pulmonary valve prevents RV → pulmonary trunk backflow.
- d) Aortic valve prevents aortic → LV regurgitation.
Q11. Cardiac output (CO) is defined as:
a) Stroke volume × Heart rate
b) Heart rate ÷ Stroke volume
c) Mean arterial pressure × Heart rate
d) Stroke volume + Heart rate
Answer: a) Stroke volume × Heart rate
Explanations:
- a) Correct — CO (L/min) = SV (mL/beat) × HR (beats/min). ✅
- b–d) Incorrect mathematical relations.
Q12. Frank–Starling mechanism refers to:
a) Increase in contractility with increased sympathetic activity
b) Increase in stroke volume proportional to end-diastolic volume (preload)
c) Afterload dependence only
d) Change in heart rate with temperature
Answer: b) Increase in stroke volume proportional to end-diastolic volume (preload)
Explanations:
- a) Sympathetic contractility is an inotropic effect, not Frank–Starling.
- b) Correct — greater venous return stretches myocardium → stronger contraction → increased SV. ✅
- c) Afterload affects SV but is not the Starling relationship.
- d) Not related.
Q13. Which ion is most important for cardiac muscle contraction coupling?
a) Sodium (Na⁺)
b) Potassium (K⁺)
c) Calcium (Ca²⁺)
d) Chloride (Cl⁻)
Answer: c) Calcium (Ca²⁺)
Explanations:
- a) Na⁺ initiates action potentials but Ca²⁺ influx triggers excitation–contraction coupling.
- b) K⁺ involved in repolarization.
- c) Calcium entry during plateau phase triggers sarcoplasmic Ca²⁺ release → contraction — correct. ✅
- d) Cl⁻ plays minor roles.
Q14. The normal resting mean arterial pressure (MAP) in a healthy adult is approximately:
a) 40 mmHg
b) 60 mmHg
c) 93–100 mmHg
d) 140 mmHg
Answer: c) 93–100 mmHg
Explanations:
- a/b/d) Incorrect ranges for normal MAP.
- c) Correct — typical MAP ≈ (1/3 systolic + 2/3 diastolic) ≈ 90–100 mmHg in adults.
Q15. Which of the following best describes the role of endothelial cells in blood vessels?
a) Passive lining only, no active function
b) Produce vasoactive substances (NO, endothelin), regulate permeability, anticoagulant properties
c) Main source of plasma proteins
d) Responsible for erythropoiesis
Answer: b) Produce vasoactive substances (NO, endothelin), regulate permeability, anticoagulant properties
Explanations:
- a) Endothelium has many active roles beyond passive lining.
- b) Correct — endothelial cells synthesize nitric oxide (vasodilator), endothelin (vasoconstrictor), regulate hemostasis, permeability, leukocyte adhesion. ✅
- c/d) Plasma proteins and erythropoiesis occur elsewhere (liver, bone marrow).
Q16. Atrial natriuretic peptide (ANP) is released from atrial myocytes in response to:
a) Low blood volume
b) Stretch of atrial wall due to increased blood volume/pressure
c) Hypokalemia only
d) Dehydration
Answer: b) Stretch of atrial wall due to increased blood volume/pressure
Explanations:
- a) ANP is released when blood volume is high, not low.
- b) Correct — atrial stretch (volume/pressure rise) stimulates ANP release → natriuresis, vasodilation, lowers blood volume/pressure. ✅
- c/d) Not primary triggers.
Q17. Which statement about capillary exchange is TRUE?
a) All capillary exchange occurs only by bulk flow (filtration)
b) Diffusion is the primary mechanism for exchange of O₂ and CO₂ across capillary walls
c) Endothelial transcytosis is the main route for small gas exchange
d) Capillaries have no role in fluid exchange
Answer: b) Diffusion is the primary mechanism for exchange of O₂ and CO₂ across capillary walls
Explanations:
- a) Bulk flow (Starling forces) governs fluid movement, but solute exchange (gases) occurs mainly by diffusion.
- b) Correct — O₂ and CO₂ cross by diffusion down partial pressure gradients. ✅
- c) Transcytosis is important for some plasma proteins and large molecules, not small gas exchange.
- d) Capillaries are central to fluid and solute exchange.
Q18. The QRS complex on ECG corresponds to:
a) Atrial depolarization
b) Ventricular depolarization and atrial repolarization (masked)
c) Ventricular repolarization
d) Cardiac mechanical contraction only
Answer: b) Ventricular depolarization and atrial repolarization (masked)
Explanations:
- a) Atrial depolarization is the P wave.
- b) Correct — QRS = ventricular depolarization; atrial repolarization occurs simultaneously but is obscured. ✅
- c) T wave = ventricular repolarization.
- d) ECG records electrical events, not directly mechanical.
Q19. The pacemaker of the heart is the:
a) Atrioventricular (AV) node
b) Sinoatrial (SA) node
c) Bundle of His
d) Purkinje fibers
Answer: b) Sinoatrial (SA) node
Explanations:
- a) AV node has slower intrinsic rate and can act as backup.
- b) SA node in the right atrium initiates normal sinus rhythm — correct. ✅
- c/d) Conduction system components downstream.
Q20. Which blood group is the universal donor for red blood cells (in emergency transfusion)?
a) AB positive
b) O negative
c) A positive
d) B negative
Answer: b) O negative
Explanations:
- a) AB+ is universal plasma donor, not universal RBC donor.
- b) O− RBCs lack A, B, and Rh antigens → minimal risk of hemolytic reaction; universal donor (for RBC transfusion). ✅
- c/d) Have antigens that can provoke reactions in recipients with antibodies.
Q21. In the ABO blood group system, a person with genotype AO expresses which phenotype?
a) Blood group A (has A antigens)
b) Blood group B
c) Blood group O
d) Blood group AB
Answer: a) Blood group A (has A antigens)
Explanations:
- a) Correct — A allele is dominant over O; AO genotype → phenotype A. ✅
- b–d) Incorrect.
Q22. Which of the following increases coronary blood flow?
a) Sympathetic α-adrenergic vasoconstriction predominating locally
b) Myocardial hypoxia producing local vasodilation (metabolic control)
c) Increased aortic diastolic pressure always decreases coronary flow
d) High systemic blood pressure always reduces coronary perfusion
Answer: b) Myocardial hypoxia producing local vasodilation (metabolic control)
Explanations:
- a) Sympathetic β2 effects and local metabolic signals override α vasoconstriction in coronary circulation.
- b) Correct — increased metabolic demand & hypoxia cause coronary vasodilation and increased flow. ✅
- c/d) Coronary perfusion is complex; perfusion mainly during diastole and responds to metabolic needs.
Q23. Mean arterial pressure (MAP) is best approximated by which formula?
a) (Systolic + Diastolic) / 2
b) Diastolic + 1/3 (Systolic − Diastolic)
c) Systolic − Diastolic
d) Systolic × Diastolic
Answer: b) Diastolic + 1/3 (Systolic − Diastolic)
Explanations:
- a) Incorrect; gives a simple average, not MAP.
- b) Correct — MAP ≈ DBP + 1/3 (PP), where PP = SBP − DBP. ✅
- c/d) Not formulas for MAP.
Q24. A patient with severe hemorrhage will initially show which compensatory cardiovascular response?
a) Decreased heart rate and vasodilation
b) Increased sympathetic activity → tachycardia and vasoconstriction to maintain BP
c) Immediate increase in urine output
d) Increased parasympathetic tone
Answer: b) Increased sympathetic activity → tachycardia and vasoconstriction to maintain BP
Explanations:
- a) Opposite of expected.
- b) Correct — baroreceptor reflex senses low BP → ↑sympathetic, ↑HR, ↑SVR to preserve perfusion. ✅
- c) Urine output decreases (aldosterone/ADH activation).
- d) Parasympathetic decreases.
Q25. Which cell type in blood is primarily responsible for clot formation (hemostasis)?
a) Erythrocytes
b) Neutrophils
c) Platelets (thrombocytes)
d) Lymphocytes
Answer: c) Platelets (thrombocytes)
Explanations:
- a) RBCs carry O₂, not primary hemostasis.
- b) Neutrophils are phagocytes for innate immunity.
- c) Platelets aggregate and provide phospholipid surface for coagulation cascade → primary hemostasis and clot formation. ✅
- d) Lymphocytes mediate adaptive immunity.
Part 2: MCQs on Human Physiology – Body Fluids and Circulation (Q26–Q50)
Q26. Which of the following is the normal blood volume in an adult human?
A) 2–3 liters
B) 4–5 liters
C) 5–6 liters
D) 7–8 liters
Answer: C) 5–6 liters
Explanation: An average adult human has 5–6 liters of blood (depending on body size, sex, and health).
Q27. What percentage of plasma is water?
A) 60–65%
B) 70–75%
C) 80–85%
D) 90–92%
Answer: D) 90–92%
Explanation: Plasma is mainly water (~92%), with proteins (7%) and other solutes like ions and nutrients.
Q28. The lifespan of human red blood cells (RBCs) is:
A) 60 days
B) 90 days
C) 120 days
D) 150 days
Answer: C) 120 days
Explanation: Human RBCs live for about 120 days, after which they are destroyed in the spleen.
Q29. Which ion is essential for the clotting of blood?
A) Na⁺
B) Ca²⁺
C) K⁺
D) Mg²⁺
Answer: B) Ca²⁺
Explanation: Calcium ions (Ca²⁺) are vital for blood coagulation by activating clotting factors.
Q30. Which chamber of the human heart pumps blood to the lungs?
A) Right atrium
B) Right ventricle
C) Left atrium
D) Left ventricle
Answer: B) Right ventricle
Explanation: The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery.
Q31. Which vessel carries oxygenated blood from the lungs to the heart?
A) Pulmonary artery
B) Pulmonary vein
C) Aorta
D) Superior vena cava
Answer: B) Pulmonary vein
Explanation: The pulmonary vein carries oxygenated blood from lungs to the left atrium.
Q32. The heart sound ‘lub’ is produced by:
A) Opening of AV valves
B) Closure of AV valves
C) Closure of semilunar valves
D) Opening of semilunar valves
Answer: B) Closure of AV valves
Explanation: The first heart sound (lub) is due to the closure of atrioventricular valves.
Q33. The second heart sound ‘dup’ is produced by:
A) Opening of AV valves
B) Closure of AV valves
C) Closure of semilunar valves
D) Opening of semilunar valves
Answer: C) Closure of semilunar valves
Explanation: The second heart sound (dup) is due to the closure of semilunar valves (aortic and pulmonary).
Q34. Which blood component transports oxygen?
A) Plasma
B) Platelets
C) Hemoglobin in RBCs
D) WBCs
Answer: C) Hemoglobin in RBCs
Explanation: Hemoglobin in RBCs binds oxygen and transports it to tissues.
Q35. Which vein carries blood from the intestine to the liver?
A) Renal vein
B) Pulmonary vein
C) Hepatic vein
D) Hepatic portal vein
Answer: D) Hepatic portal vein
Explanation: The hepatic portal vein carries nutrient-rich blood from intestines to the liver.
Q36. Normal blood pressure of an adult is:
A) 80/60 mmHg
B) 100/80 mmHg
C) 120/80 mmHg
D) 140/90 mmHg
Answer: C) 120/80 mmHg
Explanation: The average normal BP is 120 mmHg (systolic) / 80 mmHg (diastolic).
Q37. Which blood group is called the universal donor?
A) A
B) B
C) AB
D) O
Answer: D) O
Explanation: O group has no antigens, so it can be donated to all blood groups.
Q38. Which blood group is the universal recipient?
A) A
B) B
C) AB
D) O
Answer: C) AB
Explanation: AB group has no antibodies, so it can receive blood from all groups.
Q39. Which is the pacemaker of the human heart?
A) AV node
B) SA node
C) Purkinje fibers
D) Bundle of His
Answer: B) SA node
Explanation: The sinoatrial (SA) node generates electrical impulses, setting heart rhythm.
Q40. Which type of WBCs produce antibodies?
A) Neutrophils
B) Eosinophils
C) B-lymphocytes
D) T-lymphocytes
Answer: C) B-lymphocytes
Explanation: B-lymphocytes differentiate into plasma cells that secrete antibodies.
Q41. The valve between the left atrium and left ventricle is:
A) Tricuspid valve
B) Bicuspid valve
C) Semilunar valve
D) None of the above
Answer: B) Bicuspid valve
Explanation: The bicuspid/mitral valve regulates blood flow between left atrium and ventricle.
Q42. Which artery carries deoxygenated blood?
A) Aorta
B) Pulmonary artery
C) Carotid artery
D) Coronary artery
Answer: B) Pulmonary artery
Explanation: The pulmonary artery carries deoxygenated blood from right ventricle to lungs.
Q43. Which vein carries oxygenated blood?
A) Jugular vein
B) Pulmonary vein
C) Hepatic vein
D) Renal vein
Answer: B) Pulmonary vein
Explanation: Unlike other veins, pulmonary veins carry oxygenated blood from lungs.
Q44. The largest artery in the human body is:
A) Pulmonary artery
B) Aorta
C) Carotid artery
D) Coronary artery
Answer: B) Aorta
Explanation: The aorta is the largest artery, carrying oxygenated blood from heart to body.
Q45. The average heartbeat rate of a normal adult is:
A) 50–60/min
B) 70–72/min
C) 90–100/min
D) 110–120/min
Answer: B) 70–72/min
Explanation: The normal resting heart rate is about 70–72 beats per minute.
Q46. Which blood vessels have valves to prevent backflow of blood?
A) Arteries
B) Veins
C) Capillaries
D) Arterioles
Answer: B) Veins
Explanation: Valves in veins prevent backflow of blood due to low pressure.
Q47. What is the main function of platelets?
A) Transport oxygen
B) Immunity
C) Blood clotting
D) Maintain osmotic balance
Answer: C) Blood clotting
Explanation: Platelets (thrombocytes) help in blood clotting by forming a platelet plug.
Q48. Cardiac output is the product of:
A) Heart rate × Stroke volume
B) Heart rate × Blood pressure
C) Stroke volume × Blood pressure
D) Stroke volume × Blood viscosity
Answer: A) Heart rate × Stroke volume
Explanation: Cardiac output = Stroke volume × Heart rate; average ~5 liters/min.
Q49. Which part of the ECG corresponds to ventricular depolarization?
A) P wave
B) QRS complex
C) T wave
D) PR interval
Answer: B) QRS complex
Explanation: The QRS complex represents ventricular depolarization in ECG.
Q50. Which blood component is responsible for immunity?
A) Plasma
B) RBCs
C) WBCs
D) Platelets
Answer: C) WBCs
Explanation: White blood cells (especially lymphocytes) provide defense and immunity.
Part 3: Human Physiology – Body Fluids and Circulation (Q51–Q75)
Q51. Which among the following is called the pacemaker of the heart?
a) AV node
b) SA node ✅
c) Purkinje fibers
d) Bundle of His
Answer: b) SA node
Explanation: The sinoatrial (SA) node initiates the heartbeat and sets the pace, hence called the natural pacemaker of the heart.
Q52. The QRS complex in an ECG represents:
a) Atrial depolarization
b) Ventricular depolarization ✅
c) Ventricular repolarization
d) Atrial repolarization
Answer: b) Ventricular depolarization
Explanation: QRS complex corresponds to depolarization of ventricles, leading to ventricular contraction (systole).
Q53. Normal duration of a human cardiac cycle is:
a) 0.5 seconds
b) 0.6 seconds
c) 0.8 seconds ✅
d) 1.0 second
Answer: c) 0.8 seconds
Explanation: A normal cardiac cycle lasts about 0.8 seconds, with 72 beats per minute on average.
Q54. Which blood vessel carries oxygenated blood from lungs to the heart?
a) Pulmonary vein ✅
b) Pulmonary artery
c) Aorta
d) Coronary vein
Answer: a) Pulmonary vein
Explanation: Pulmonary veins carry oxygen-rich blood from lungs to the left atrium.
Q55. Which layer of the heart is responsible for contraction?
a) Endocardium
b) Epicardium
c) Myocardium ✅
d) Pericardium
Answer: c) Myocardium
Explanation: Myocardium is the thick muscular layer of the heart responsible for pumping action.
Q56. The double circulation in humans means:
a) Blood passes twice through lungs
b) Blood passes twice through heart in one cycle ✅
c) Blood passes twice through arteries
d) Blood circulates in two directions
Answer: b) Blood passes twice through heart in one cycle
Explanation: In double circulation, blood flows through the heart twice in a complete circulation—pulmonary and systemic.
Q57. Which of the following has the thickest walls?
a) Veins
b) Arteries ✅
c) Capillaries
d) Venules
Answer: b) Arteries
Explanation: Arteries have thick muscular walls to withstand high pressure of blood pumped from heart.
Q58. Which valve prevents backflow of blood from right ventricle to right atrium?
a) Bicuspid valve
b) Tricuspid valve ✅
c) Semilunar valve
d) Aortic valve
Answer: b) Tricuspid valve
Explanation: Tricuspid valve prevents backflow of blood during ventricular contraction.
Q59. Which of the following blood components is responsible for clotting?
a) RBC
b) WBC
c) Platelets ✅
d) Plasma
Answer: c) Platelets
Explanation: Platelets release thromboplastin, initiating clot formation.
Q60. Which ion is essential for blood clotting?
a) Sodium
b) Potassium
c) Calcium ✅
d) Chloride
Answer: c) Calcium
Explanation: Ca²⁺ ions are necessary for activation of clotting factors during blood coagulation.
Q61. Pulmonary circulation carries blood between:
a) Heart and body tissues
b) Heart and lungs ✅
c) Heart and brain
d) Heart and kidneys
Answer: b) Heart and lungs
Explanation: Pulmonary circulation is the movement of deoxygenated blood from the heart to the lungs and oxygenated blood back to the heart.
Q62. Which type of blood vessel has valves?
a) Arteries
b) Veins ✅
c) Capillaries
d) Arterioles
Answer: b) Veins
Explanation: Valves in veins prevent backflow of blood under low pressure.
Q63. What is the main function of systemic circulation?
a) Carry blood to lungs
b) Supply oxygenated blood to body tissues ✅
c) Filter blood in kidneys
d) Circulate blood only in brain
Answer: b) Supply oxygenated blood to body tissues
Explanation: Systemic circulation delivers oxygen and nutrients to tissues and removes waste.
Q64. Which heart chamber pumps blood into the aorta?
a) Left atrium
b) Left ventricle ✅
c) Right atrium
d) Right ventricle
Answer: b) Left ventricle
Explanation: Left ventricle pumps oxygenated blood into the aorta under high pressure.
Q65. The pacemaker of heart is located in:
a) Right atrium ✅
b) Left atrium
c) Right ventricle
d) Left ventricle
Answer: a) Right atrium
Explanation: SA node, the natural pacemaker, is located in the wall of right atrium.
Q66. Normal heart rate in humans is:
a) 50–60/min
b) 70–80/min ✅
c) 90–100/min
d) 110–120/min
Answer: b) 70–80/min
Explanation: The normal resting heart rate is about 72 beats per minute in a healthy adult.
Q67. Which of the following is the correct sequence of cardiac conduction system?
a) SA node → Purkinje fibers → AV node → Bundle of His
b) SA node → AV node → Bundle of His → Purkinje fibers ✅
c) AV node → SA node → Bundle of His → Purkinje fibers
d) Purkinje fibers → SA node → AV node → Bundle of His
Answer: b) SA node → AV node → Bundle of His → Purkinje fibers
Explanation: This is the normal pathway of conduction for proper rhythmic contraction of heart.
Q68. Which blood group is known as universal donor?
a) A
b) B
c) AB
d) O ✅
Answer: d) O
Explanation: O blood group lacks antigens, hence can be donated to any group (O- is universal donor).
Q69. Which blood group is known as universal recipient?
a) O
b) AB ✅
c) A
d) B
Answer: b) AB
Explanation: AB blood group lacks antibodies, hence can receive blood from any group.
Q70. Which component of ECG represents atrial depolarization?
a) P wave ✅
b) QRS complex
c) T wave
d) ST segment
Answer: a) P wave
Explanation: P wave shows depolarization of atria, leading to atrial contraction.
Q71. The closing of semilunar valves produces which heart sound?
a) Lub
b) Dub ✅
c) Murmur
d) None
Answer: b) Dub
Explanation: The second heart sound “dub” is due to closing of semilunar valves at the start of ventricular diastole.
Q72. Cardiac output is the product of:
a) Heart rate × Stroke volume ✅
b) Stroke volume × Blood pressure
c) Heart rate × Blood pressure
d) Stroke volume × TPR
Answer: a) Heart rate × Stroke volume
Explanation: Cardiac output = 72 beats/min × 70 mL = ~5 liters/min.
Q73. Which of the following blood vessels carries deoxygenated blood?
a) Pulmonary vein
b) Pulmonary artery ✅
c) Aorta
d) Carotid artery
Answer: b) Pulmonary artery
Explanation: Pulmonary artery carries deoxygenated blood from right ventricle to lungs.
Q74. Which hormone increases heart rate?
a) Thyroxine
b) Adrenaline ✅
c) Insulin
d) Cortisol
Answer: b) Adrenaline
Explanation: Adrenaline (epinephrine) stimulates the SA node, increasing heart rate during stress/excitement.
Q75. Which of the following is a granulocyte?
a) Lymphocyte
b) Monocyte
c) Eosinophil ✅
d) Platelet
Answer: c) Eosinophil
Explanation: Granulocytes include neutrophils, eosinophils, and basophils. Lymphocytes and monocytes are agranulocytes.
Part 4: Human Physiology – Body Fluids and Circulation MCQs (Q76–Q100)
Q76. Which blood vessels are known as the exchange vessels of the body?
a) Arteries
b) Veins
c) Capillaries ✅
d) Arterioles
Answer: c) Capillaries
Explanation: Capillaries have thin walls (one-cell thick endothelium) that allow exchange of gases, nutrients, and wastes between blood and tissues.
Q77. The longest vein in the human body is:
a) Jugular vein
b) Hepatic vein
c) Great saphenous vein ✅
d) Femoral vein
Answer: c) Great saphenous vein
Explanation: The great saphenous vein runs along the leg and is the longest vein in the human body.
Q78. Which heart valve prevents backflow of blood into the left atrium?
a) Tricuspid valve
b) Bicuspid (mitral) valve ✅
c) Semilunar valve
d) Pulmonary valve
Answer: b) Bicuspid (mitral) valve
Explanation: The bicuspid (mitral) valve is located between the left atrium and left ventricle; it prevents backflow of blood.
Q79. Which blood group is known as the universal recipient?
a) O–
b) O+
c) AB+ ✅
d) AB–
Answer: c) AB+
Explanation: AB+ blood group can receive blood from all groups as it has no antibodies (anti-A or anti-B) and Rh+ factor.
Q80. Which component of blood is responsible for clotting?
a) RBCs
b) Platelets ✅
c) WBCs
d) Plasma proteins only
Answer: b) Platelets
Explanation: Platelets release thromboplastin that helps convert prothrombin to thrombin, initiating blood clotting.
Q81. Which vein carries oxygenated blood?
a) Pulmonary vein ✅
b) Hepatic vein
c) Jugular vein
d) Renal vein
Answer: a) Pulmonary vein
Explanation: The pulmonary vein carries oxygenated blood from lungs to the left atrium, unlike other veins.
Q82. Which artery carries deoxygenated blood?
a) Pulmonary artery ✅
b) Carotid artery
c) Aorta
d) Coronary artery
Answer: a) Pulmonary artery
Explanation: The pulmonary artery carries deoxygenated blood from right ventricle to lungs for oxygenation.
Q83. What is the normal pH of blood?
a) 6.8–7.0
b) 7.35–7.45 ✅
c) 7.8–8.0
d) 6.0–6.5
Answer: b) 7.35–7.45
Explanation: Blood is slightly alkaline, maintaining a pH range of 7.35–7.45, regulated by buffers.
Q84. Which protein in plasma maintains osmotic pressure?
a) Globulin
b) Fibrinogen
c) Albumin ✅
d) Hemoglobin
Answer: c) Albumin
Explanation: Albumin is the main plasma protein that maintains osmotic pressure and prevents plasma leakage.
Q85. The pacemaker of the human heart is:
a) AV node
b) Purkinje fibers
c) SA node ✅
d) Bundle of His
Answer: c) SA node
Explanation: SA node (sinoatrial node) in the right atrium initiates heartbeat and is called the pacemaker.
Q86. In fetal circulation, which structure allows blood to bypass the lungs?
a) Foramen ovale ✅
b) Ductus arteriosus
c) Ductus venosus
d) Umbilical artery
Answer: a) Foramen ovale
Explanation: Foramen ovale is an opening between atria in the fetal heart allowing blood to bypass lungs.
Q87. Which artery supplies blood to the heart muscle?
a) Pulmonary artery
b) Coronary artery ✅
c) Carotid artery
d) Subclavian artery
Answer: b) Coronary artery
Explanation: Coronary arteries branch from the aorta and supply oxygenated blood to heart tissues.
Q88. Which chamber of the heart pumps blood into systemic circulation?
a) Right atrium
b) Left atrium
c) Right ventricle
d) Left ventricle ✅
Answer: d) Left ventricle
Explanation: Left ventricle pumps oxygenated blood through aorta into systemic circulation.
Q89. Which vitamin is essential for blood clotting?
a) Vitamin A
b) Vitamin B12
c) Vitamin K ✅
d) Vitamin D
Answer: c) Vitamin K
Explanation: Vitamin K is essential for synthesis of prothrombin and clotting factors.
Q90. What is the function of lymph nodes?
a) Produce erythrocytes
b) Trap pathogens ✅
c) Store platelets
d) Store bile
Answer: b) Trap pathogens
Explanation: Lymph nodes filter lymph and trap pathogens, also producing lymphocytes.
Q91. Which blood group is known as the universal donor?
a) AB+
b) AB–
c) O– ✅
d) O+
Answer: c) O–
Explanation: O– blood group lacks A, B, and Rh antigens; thus, it can be donated to any group.
Q92. Which part of ECG represents ventricular depolarization?
a) P wave
b) QRS complex ✅
c) T wave
d) PR interval
Answer: b) QRS complex
Explanation: QRS complex represents ventricular depolarization leading to ventricular contraction.
Q93. Which ion plays the most important role in blood clotting?
a) Sodium
b) Potassium
c) Calcium ✅
d) Chloride
Answer: c) Calcium
Explanation: Calcium ions (Ca²⁺) are essential cofactors for the conversion of prothrombin to thrombin.
Q94. Which blood component transports CO₂ in the highest proportion?
a) Dissolved in plasma
b) Carbaminohemoglobin
c) Bicarbonate ions ✅
d) Carbonic acid
Answer: c) Bicarbonate ions
Explanation: About 70% of CO₂ is transported as bicarbonate ions in plasma.
Q95. Which organ produces erythropoietin?
a) Liver
b) Kidney ✅
c) Pancreas
d) Bone marrow
Answer: b) Kidney
Explanation: Erythropoietin is secreted by kidneys and stimulates RBC production in bone marrow.
Q96. Which vein carries nutrient-rich blood from intestine to liver?
a) Hepatic vein
b) Hepatic portal vein ✅
c) Renal vein
d) Jugular vein
Answer: b) Hepatic portal vein
Explanation: Hepatic portal vein carries nutrient-rich blood from gut to liver for metabolism.
Q97. The first heart sound “lub” is due to closure of:
a) Semilunar valves
b) AV valves ✅
c) Pulmonary valve
d) Aortic valve
Answer: b) AV valves
Explanation: The “lub” sound is caused by closure of tricuspid and bicuspid (AV) valves at systole.
Q98. The second heart sound “dub” is caused by closure of:
a) AV valves
b) Semilunar valves ✅
c) Mitral valve
d) Tricuspid valve
Answer: b) Semilunar valves
Explanation: The “dub” sound is due to closure of aortic and pulmonary semilunar valves at diastole.
Q99. In humans, the number of WBCs per mm³ of blood is approximately:
a) 1,000–2,000
b) 5,000–10,000 ✅
c) 20,000–30,000
d) 50,000–80,000
Answer: b) 5,000–10,000
Explanation: Normal WBC count ranges between 5,000–10,000 per mm³ of blood.
Q100. Which layer of the heart is responsible for contraction?
a) Endocardium
b) Myocardium ✅
c) Epicardium
d) Pericardium
Answer: b) Myocardium
Explanation: Myocardium, the thick muscular middle layer of the heart, is responsible for pumping contractions.
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