1. Which embryonic germ layer gives rise to the human heart?
Correct Answer: B (Mesoderm)
The circulatory system, including the heart, blood vessels, and blood cells, is mesodermal in embryonic origin.
The circulatory system, including the heart, blood vessels, and blood cells, is mesodermal in embryonic origin.
2. What percentage of total blood volume is constituted by plasma?
Correct Answer: B (55%)
Blood consists of a fluid matrix called plasma (about 55%) and formed elements (about 45%).
Blood consists of a fluid matrix called plasma (about 55%) and formed elements (about 45%).
3. Which plasma protein is primarily responsible for maintaining colloid osmotic pressure?
Correct Answer: C (Albumin)
Albumins are the most abundant plasma proteins and play a major role in maintaining osmotic balance.
Albumins are the most abundant plasma proteins and play a major role in maintaining osmotic balance.
4. What is the average lifespan of human red blood cells (erythrocytes)?
Correct Answer: C (120 days)
RBCs have an average lifespan of 120 days, after which they are destroyed primarily in the spleen.
RBCs have an average lifespan of 120 days, after which they are destroyed primarily in the spleen.
5. Which organ is universally termed the “graveyard of RBCs”?
Correct Answer: B (Spleen)
Worn-out and damaged red blood cells are filtered out and broken down in the spleen.
Worn-out and damaged red blood cells are filtered out and broken down in the spleen.
6. Which is the most abundant type of white blood cell in human blood?
Correct Answer: A (Neutrophils)
Neutrophils constitute approximately 60–65% of the total WBC count and function as phagocytes.
Neutrophils constitute approximately 60–65% of the total WBC count and function as phagocytes.
7. Histamine, serotonin, and heparin are secreted by which leukocytes?
Correct Answer: C (Basophils)
Basophils secrete histamine, serotonin, and heparin, and are involved in inflammatory and allergic reactions.
Basophils secrete histamine, serotonin, and heparin, and are involved in inflammatory and allergic reactions.
8. Platelets (thrombocytes) are cell fragments derived from:
Correct Answer: B (Megakaryocytes)
Megakaryocytes are special large cells in the bone marrow that fragment to produce platelets.
Megakaryocytes are special large cells in the bone marrow that fragment to produce platelets.
9. What is the normal platelet count in a healthy adult human?
Correct Answer: B (150,000 – 350,000 / mm³)
A normal blood count contains 1.5 to 3.5 lakh (150,000 to 350,000) platelets per cubic millimeter.
A normal blood count contains 1.5 to 3.5 lakh (150,000 to 350,000) platelets per cubic millimeter.
10. An individual with blood group ‘O’ possesses:
Correct Answer: C (No surface antigens, but both anti-A and anti-B antibodies)
Blood group O RBCs lack A and B surface agglutinogens, but plasma contains both anti-A and anti-B agglutinins.
Blood group O RBCs lack A and B surface agglutinogens, but plasma contains both anti-A and anti-B agglutinins.
11. Which blood group is universally known as the universal recipient?
Correct Answer: C (AB Rh-positive)
AB positive individuals lack anti-A, anti-B, and anti-Rh antibodies in plasma, allowing them to receive any ABO/Rh blood type.
AB positive individuals lack anti-A, anti-B, and anti-Rh antibodies in plasma, allowing them to receive any ABO/Rh blood type.
12. Erythroblastosis foetalis can occur when:
Correct Answer: B (Mother is Rh-ve and fetus is Rh+ve)
Maternal anti-Rh antibodies cross the placenta in subsequent pregnancies and destroy Rh+ fetal RBCs.
Maternal anti-Rh antibodies cross the placenta in subsequent pregnancies and destroy Rh+ fetal RBCs.
13. Which mineral ion is essential for the blood coagulation cascade?
Correct Answer: C (Ca²⁺)
Calcium ions (Factor IV) are crucial cofactors at multiple enzymatic steps of the blood clotting cascade.
Calcium ions (Factor IV) are crucial cofactors at multiple enzymatic steps of the blood clotting cascade.
14. The inactive enzyme prothrombin is converted into active thrombin by:
Correct Answer: B (Thrombokinase (Prothrombinase))
Thrombokinase complex catalyses the conversion of prothrombin to active thrombin in the presence of calcium.
Thrombokinase complex catalyses the conversion of prothrombin to active thrombin in the presence of calcium.
15. How does lymph differ compositionally from blood plasma?
Correct Answer: B (It is devoid of RBCs and contains fewer large proteins)
Lymph lacks erythrocytes, has lower protein concentrations than plasma, but is rich in specialized lymphocytes.
Lymph lacks erythrocytes, has lower protein concentrations than plasma, but is rich in specialized lymphocytes.
16. Specialized lymphatic capillaries that absorb dietary fats in intestinal villi are called:
Correct Answer: B (Lacteals)
Lacteals absorb dietary fats (packaged into chylomicrons) in the microvilli of the small intestine.
Lacteals absorb dietary fats (packaged into chylomicrons) in the microvilli of the small intestine.
17. An open circulatory system is characteristically found in:
Correct Answer: A (Arthropods and non-cephalopod Molluscs)
Arthropods and molluscs possess open circulatory systems where hemolymph bathes open sinus cavities.
Arthropods and molluscs possess open circulatory systems where hemolymph bathes open sinus cavities.
18. A two-chambered heart with single-circuit circulation is found in:
Correct Answer: C (Fishes)
Fishes possess a 2-chambered heart (one atrium, one ventricle) pumping deoxygenated venous blood to gills.
Fishes possess a 2-chambered heart (one atrium, one ventricle) pumping deoxygenated venous blood to gills.
19. Which reptile possesses a completely partitioned 4-chambered heart?
Correct Answer: C (Crocodilus (Crocodile))
Crocodilians are an exception among non-avian reptiles in having a fully divided four-chambered heart.
Crocodilians are an exception among non-avian reptiles in having a fully divided four-chambered heart.
20. The double-walled membranous bag enclosing the human heart is called the:
Correct Answer: B (Pericardium)
The heart is enclosed by the pericardial sac, which contains lubricating pericardial fluid to reduce friction.
The heart is enclosed by the pericardial sac, which contains lubricating pericardial fluid to reduce friction.
21. The natural pacemaker of the human heart is the:
Correct Answer: A (Sinoatrial (SA) node)
The SA node generates rhythmic action potentials at the highest frequency (70–75/min), dictating heart rate.
The SA node generates rhythmic action potentials at the highest frequency (70–75/min), dictating heart rate.
22. Where is the Sinoatrial (SA) node anatomically situated?
Correct Answer: A (Right upper corner of right atrium)
The SA node is located in the upper right wall of the right atrium near the opening of the superior vena cava.
The SA node is located in the upper right wall of the right atrium near the opening of the superior vena cava.
23. The bicuspid (mitral) valve guards the opening between:
Correct Answer: B (Left atrium and left ventricle)
The bicuspid (or mitral) valve prevents backflow of blood from the left ventricle to the left atrium.
The bicuspid (or mitral) valve prevents backflow of blood from the left ventricle to the left atrium.
24. The tricuspid valve is situated between the:
Correct Answer: A (Right atrium and right ventricle)
The tricuspid valve consists of three muscular cusps guarding the right atrioventricular aperture.
The tricuspid valve consists of three muscular cusps guarding the right atrioventricular aperture.
25. Fibrous cords attaching AV valve cusps to ventricular papillary muscles are:
Correct Answer: B (Chordae tendineae)
Chordae tendineae anchor valve flaps to papillary muscles, preventing valve inversion during ventricular systole.
Chordae tendineae anchor valve flaps to papillary muscles, preventing valve inversion during ventricular systole.
26. Semilunar valves are located at the base of the:
Correct Answer: B (Aorta and pulmonary artery)
Semilunar valves prevent arterial blood from backflowing into ventricles during ventricular diastole.
Semilunar valves prevent arterial blood from backflowing into ventricles during ventricular diastole.
27. What is the total duration of a single standard cardiac cycle at 75 bpm?
Correct Answer: C (0.8 second)
At 75 beats/minute, duration of one cardiac cycle = 60 / 75 = 0.8 seconds.
At 75 beats/minute, duration of one cardiac cycle = 60 / 75 = 0.8 seconds.
28. During a cardiac cycle, the duration of ventricular systole is approximately:
Correct Answer: B (0.3 s)
A complete cycle (0.8s) comprises atrial systole (0.1s), ventricular systole (0.3s), and joint diastole (0.4s).
A complete cycle (0.8s) comprises atrial systole (0.1s), ventricular systole (0.3s), and joint diastole (0.4s).
29. The standard volume of blood pumped by each ventricle during a single contraction (stroke volume) is:
Correct Answer: B (70 mL)
Stroke volume in a healthy resting adult is roughly 70 mL per beat.
Stroke volume in a healthy resting adult is roughly 70 mL per beat.
30. How is cardiac output calculated mathematically?
Correct Answer: B (Stroke Volume × Heart Rate)
Cardiac Output = SV × HR (e.g., 70 mL × 72 bpm ≈ 5040 mL/min or ~5 L/min).
Cardiac Output = SV × HR (e.g., 70 mL × 72 bpm ≈ 5040 mL/min or ~5 L/min).
31. The first heart sound (‘lub’) is caused by the closure of the:
Correct Answer: A (Tricuspid and Bicuspid (AV) valves)
‘Lub’ marks the onset of ventricular systole and results from the sudden closure of AV valves.
‘Lub’ marks the onset of ventricular systole and results from the sudden closure of AV valves.
32. The second heart sound (‘dub’) is produced by the closure of:
Correct Answer: C (Semilunar valves)
‘Dub’ is sharper and shorter, produced at the onset of ventricular diastole as semilunar valves snap shut.
‘Dub’ is sharper and shorter, produced at the onset of ventricular diastole as semilunar valves snap shut.
33. On a standard ECG recording, what does the P-wave represent?
Correct Answer: A (Depolarization of the atria)
The P-wave corresponds to electrical excitation (depolarization) of both atria leading to atrial contraction.
The P-wave corresponds to electrical excitation (depolarization) of both atria leading to atrial contraction.
34. The QRS complex in an ECG represents:
Correct Answer: B (Ventricular depolarization)
The QRS complex indicates rapid ventricular depolarization, initiating ventricular systole.
The QRS complex indicates rapid ventricular depolarization, initiating ventricular systole.
35. What physiological event does the T-wave represent on an ECG?
Correct Answer: B (Ventricular repolarization)
The T-wave marks the return of ventricles from excited to normal polarized state (ventricular relaxation).
The T-wave marks the return of ventricles from excited to normal polarized state (ventricular relaxation).
36. Counting the number of which ECG features provides the patient’s heart rate?
Correct Answer: B (QRS complexes)
Since each QRS complex represents a single ventricular beat, the number of QRS complexes per minute equals heart rate.
Since each QRS complex represents a single ventricular beat, the number of QRS complexes per minute equals heart rate.
37. The smooth inner endothelial lining of blood vessels is termed:
Correct Answer: C (Tunica intima)
Tunica intima is the innermost layer composed of squamous endothelium lining the vessel lumen.
Tunica intima is the innermost layer composed of squamous endothelium lining the vessel lumen.
38. Which blood vessel carries deoxygenated blood from the heart to the lungs?
Correct Answer: B (Pulmonary artery)
The pulmonary artery emerges from the right ventricle and transports deoxygenated blood to the lungs.
The pulmonary artery emerges from the right ventricle and transports deoxygenated blood to the lungs.
39. Oxygenated blood from the lungs is carried to the left atrium via:
Correct Answer: A (Pulmonary veins)
Four pulmonary veins (two from each lung) deliver oxygenated blood directly into the left atrium.
Four pulmonary veins (two from each lung) deliver oxygenated blood directly into the left atrium.
40. The hepatic portal vein drains nutrient-rich blood from the digestive tract into the:
Correct Answer: C (Liver)
The hepatic portal system carries blood from the gut and spleen to the liver before it enters systemic circulation.
The hepatic portal system carries blood from the gut and spleen to the liver before it enters systemic circulation.
41. The neural center that regulates cardiovascular activities is located in the:
Correct Answer: C (Medulla oblongata)
The cardiovascular center in the medulla oblongata moderates cardiac function via the autonomic nervous system.
The cardiovascular center in the medulla oblongata moderates cardiac function via the autonomic nervous system.
42. Stimulation by the sympathetic nervous system results in:
Correct Answer: A (Increased heart rate and force of contraction)
Sympathetic signals (via noradrenaline) elevate heart rate, ventricular contractile strength, and cardiac output.
Sympathetic signals (via noradrenaline) elevate heart rate, ventricular contractile strength, and cardiac output.
43. Parasympathetic neural signals (via the vagus nerve) affect the heart by:
Correct Answer: B (Decreasing heart rate and action potential conduction speed)
Parasympathetic stimulation releases acetylcholine, decreasing SA nodal firing rate and slowing AV conduction.
Parasympathetic stimulation releases acetylcholine, decreasing SA nodal firing rate and slowing AV conduction.
44. Clinical hypertension in adults is diagnosed when resting blood pressure consistently exceeds:
Correct Answer: C (140/90 mm Hg)
Repeated blood pressure measurements of 140/90 mm Hg or higher confirm clinical hypertension.
Repeated blood pressure measurements of 140/90 mm Hg or higher confirm clinical hypertension.
45. Atherosclerosis is characterized pathologically by the deposition of:
Correct Answer: A (Calcium, fat, cholesterol, and fibrous tissue in arteries)
Coronary Artery Disease (Atherosclerosis) involves plaque buildup that narrows arterial lumens.
Coronary Artery Disease (Atherosclerosis) involves plaque buildup that narrows arterial lumens.
46. The medical symptom of acute crushing chest pain caused by insufficient myocardial oxygen is:
Correct Answer: B (Angina pectoris)
Angina pectoris occurs when myocardial oxygen demand outstrips coronary blood supply.
Angina pectoris occurs when myocardial oxygen demand outstrips coronary blood supply.
47. Heart failure is clinically defined as:
Correct Answer: C (Inability of the heart to pump blood effectively to meet tissue needs)
Heart failure is the state of heart when it does not pump blood effectively; often called congestive heart failure.
Heart failure is the state of heart when it does not pump blood effectively; often called congestive heart failure.
48. Why is the human heart termed ‘myogenic’?
Correct Answer: B (Impulse of contraction is generated intrinsically by modified nodal musculature)
The human heart generates its auto-excitatory action potentials within specialized nodal tissue without neural triggers.
The human heart generates its auto-excitatory action potentials within specialized nodal tissue without neural triggers.
49. Which blood vessels possess valves to prevent backward flow of blood under low pressure?
Correct Answer: C (Veins)
Veins contain unidirectional semilunar-like pocket valves to maintain venous return against gravity.
Veins contain unidirectional semilunar-like pocket valves to maintain venous return against gravity.
50. The wall of which heart chamber possesses the thickest myocardium?
Correct Answer: D (Left ventricle)
The left ventricle pumps against high systemic vascular resistance, requiring a muscular wall ~3x thicker than the right.
The left ventricle pumps against high systemic vascular resistance, requiring a muscular wall ~3x thicker than the right.
51. The opening of the inferior vena cava into the right atrium is guarded embryologically by the:
Correct Answer: A (Eustachian valve)
The Eustachian valve directs incoming oxygenated blood from the IVC toward the foramen ovale in fetal life.
The Eustachian valve directs incoming oxygenated blood from the IVC toward the foramen ovale in fetal life.
52. The opening of the coronary sinus into the right atrium is guarded by the:
Correct Answer: B (Thebesian valve)
The Thebesian (coronary) valve prevents regurgitation of blood into the coronary sinus during atrial systole.
The Thebesian (coronary) valve prevents regurgitation of blood into the coronary sinus during atrial systole.
53. The remnant of the fetal foramen ovale in the adult interatrial septum is called the:
Correct Answer: A (Fossa ovalis)
The fossa ovalis is a shallow depression in the right atrium marking the closed fetal interatrial shunt.
The fossa ovalis is a shallow depression in the right atrium marking the closed fetal interatrial shunt.
54. In human fetuses, the ductus arteriosus connects the pulmonary artery directly to the:
Correct Answer: B (Aorta)
Ductus arteriosus shunts blood away from non-functioning fetal lungs directly into the systemic aorta.
Ductus arteriosus shunts blood away from non-functioning fetal lungs directly into the systemic aorta.
55. Which clotting factor is also known as the Christmas Factor?
Correct Answer: B (Factor IX)
Factor IX is Christmas Factor; its congenital deficiency causes Hemophilia B (Christmas disease).
Factor IX is Christmas Factor; its congenital deficiency causes Hemophilia B (Christmas disease).
56. What is the normal physiological pH range of human arterial blood?
Correct Answer: C (7.35 – 7.45)
Human blood is slightly alkaline, strictly maintained within the homeostatic window of 7.35 to 7.45.
Human blood is slightly alkaline, strictly maintained within the homeostatic window of 7.35 to 7.45.
57. Which agranulocyte transforms into a tissue macrophage upon extravasation?
Correct Answer: B (Monocyte)
Monocytes circulate in blood and migrate into peripheral tissues where they differentiate into macrophages.
Monocytes circulate in blood and migrate into peripheral tissues where they differentiate into macrophages.
58. The process of white blood cells squeezing through intact capillary walls is called:
Correct Answer: A (Diapedesis)
Diapedesis (or extravasation) is the amoeboid transmigration of leukocytes across vascular endothelial walls.
Diapedesis (or extravasation) is the amoeboid transmigration of leukocytes across vascular endothelial walls.
59. Serum is best defined biochemically as:
Correct Answer: B (Plasma – Clotting factors)
Serum is blood plasma from which fibrinogen and other clotting cascade proteins have been removed.
Serum is blood plasma from which fibrinogen and other clotting cascade proteins have been removed.
60. Which vitamin is an indispensable cofactor for hepatic synthesis of prothrombin?
Correct Answer: C (Vitamin K)
Vitamin K is essential for gamma-carboxylation of clotting factors II (prothrombin), VII, IX, and X.
Vitamin K is essential for gamma-carboxylation of clotting factors II (prothrombin), VII, IX, and X.
61. An abnormal elevation in total Red Blood Cell count is termed:
Correct Answer: C (Polycythemia)
Polycythemia refers to an increased hematocrit/RBC mass, often seen at high altitudes or in myeloproliferative diseases.
Polycythemia refers to an increased hematocrit/RBC mass, often seen at high altitudes or in myeloproliferative diseases.
62. Which blood vessels have the highest total cross-sectional area and slowest velocity of blood flow?
Correct Answer: B (Capillaries)
Capillary beds have the greatest aggregate surface area, minimizing flow speed to optimize nutrient-gas exchange.
Capillary beds have the greatest aggregate surface area, minimizing flow speed to optimize nutrient-gas exchange.
63. Intercalated discs with gap junctions are unique histological hallmarks of:
Correct Answer: C (Cardiac muscle)
Intercalated discs contain desmosomes and gap junctions that allow the myocardium to contract as a functional syncytium.
Intercalated discs contain desmosomes and gap junctions that allow the myocardium to contract as a functional syncytium.
64. The intrinsic rate of impulse generation by the Atrioventricular (AV) node is:
Correct Answer: B (40 – 60 / min)
If the SA node fails, the AV node assumes pacing duties at its inherent rate of 40–60 action potentials per minute.
If the SA node fails, the AV node assumes pacing duties at its inherent rate of 40–60 action potentials per minute.
65. What causes the characteristic 0.1-second delay at the AV node?
Correct Answer: B (To allow complete atrial emptying before ventricular contraction)
The AV nodal delay ensures atria finish ejecting their blood volume into the ventricles before ventricular systole starts.
The AV nodal delay ensures atria finish ejecting their blood volume into the ventricles before ventricular systole starts.
66. The Instrument used clinically to measure arterial blood pressure is the:
Correct Answer: B (Sphygmomanometer)
A sphygmomanometer with an inflatable cuff is used alongside a stethoscope to record systolic and diastolic pressures.
A sphygmomanometer with an inflatable cuff is used alongside a stethoscope to record systolic and diastolic pressures.
67. The difference between systolic and diastolic blood pressure is termed:
Correct Answer: B (Pulse pressure)
Pulse Pressure = Systolic Pressure − Diastolic Pressure (normally 120 − 80 = 40 mm Hg).
Pulse Pressure = Systolic Pressure − Diastolic Pressure (normally 120 − 80 = 40 mm Hg).
68. How is Mean Arterial Pressure (MAP) estimated clinically?
Correct Answer: A (Diastolic Pressure + 1/3 (Pulse Pressure))
Because diastole lasts longer than systole, MAP ≈ Diastolic BP + 1/3(SBP – DBP).
Because diastole lasts longer than systole, MAP ≈ Diastolic BP + 1/3(SBP – DBP).
69. The main hormone secreted by atrial myocardium in response to high wall stretch is:
Correct Answer: C (Atrial Natriuretic Peptide (ANP))
ANP triggers vasodilation and renal sodium/water excretion, thereby reducing blood volume and blood pressure.
ANP triggers vasodilation and renal sodium/water excretion, thereby reducing blood volume and blood pressure.
70. An abnormal decrease in circulating white blood cells (< 4,000/mm³) is termed:
Correct Answer: B (Leukopenia)
Leukopenia is an abnormally low WBC count, increasing vulnerability to opportunistic infections.
Leukopenia is an abnormally low WBC count, increasing vulnerability to opportunistic infections.
71. An elevation in resting heart rate above 100 beats per minute is termed:
Correct Answer: A (Tachycardia)
Tachycardia is defined as a resting heart rate > 100 bpm; bradycardia is < 60 bpm.
Tachycardia is defined as a resting heart rate > 100 bpm; bradycardia is < 60 bpm.
72. Which artery supplies oxygenated blood directly to the heart wall musculature?
Correct Answer: C (Coronary artery)
Right and left coronary arteries branch off the base of the ascending aorta to perfuse cardiac muscle.
Right and left coronary arteries branch off the base of the ascending aorta to perfuse cardiac muscle.
73. A persistent resting heart rate below 60 beats per minute in non-athletes is called:
Correct Answer: B (Bradycardia)
Bradycardia refers to an abnormally slow heart rhythm under 60 bpm.
Bradycardia refers to an abnormally slow heart rhythm under 60 bpm.
74. The primary physiological site of erythropoiesis in healthy human adults is:
Correct Answer: C (Red bone marrow)
Adult hematopoiesis/erythropoiesis occurs primarily within the trabecular cavities of red bone marrow.
Adult hematopoiesis/erythropoiesis occurs primarily within the trabecular cavities of red bone marrow.
75. The hormone erythropoietin (EPO), which stimulates RBC generation, is synthesized by:
Correct Answer: B (Juxtaglomerular cells of the kidney)
Renal hypoxia triggers juxtaglomerular cells to secrete erythropoietin into the bloodstream.
Renal hypoxia triggers juxtaglomerular cells to secrete erythropoietin into the bloodstream.
76. Which antibodies are naturally present in the plasma of a type ‘AB’ blood individual?
Correct Answer: D (Neither Anti-A nor Anti-B)
Type AB plasma contains no ABO agglutinins, preventing auto-hemolysis of its A and B antigen-bearing RBCs.
Type AB plasma contains no ABO agglutinins, preventing auto-hemolysis of its A and B antigen-bearing RBCs.
77. The middle muscular, contractile tunic of an artery is the:
Correct Answer: B (Tunica media)
Tunica media is composed of smooth muscle and elastic fibers, controlling vessel diameter and resistance.
Tunica media is composed of smooth muscle and elastic fibers, controlling vessel diameter and resistance.
78. The primary function of eosinophils is to:
Correct Answer: C (Resist parasitic infections and modulate allergic responses)
Eosinophils release cytotoxic enzymes against helminth parasites and degrade histamine in allergic reactions.
Eosinophils release cytotoxic enzymes against helminth parasites and degrade histamine in allergic reactions.
79. Frank-Starling law of the heart states that:
Correct Answer: A (Stroke volume increases proportionally with increased end-diastolic volume (myocardial stretch))
Greater end-diastolic volume stretches myocardial fibers, optimizing actin-myosin overlap and contractile force.
Greater end-diastolic volume stretches myocardial fibers, optimizing actin-myosin overlap and contractile force.
80. The volume of blood remaining in each ventricle at the end of ventricular systole is:
Correct Answer: B (End-Systolic Volume (~50 mL))
End-Systolic Volume (ESV) is the residual ventricular blood volume (~50 mL) following contraction.
End-Systolic Volume (ESV) is the residual ventricular blood volume (~50 mL) following contraction.
81. Capillary walls consist exclusively of which single histological layer?
Correct Answer: A (Simple squamous endothelium and basement membrane)
Capillaries lack tunica media and externa, consisting only of a delicate monolayer of endothelial cells.
Capillaries lack tunica media and externa, consisting only of a delicate monolayer of endothelial cells.
82. Which endogenous anticoagulant is produced by mast cells and basophils?
Correct Answer: B (Heparin)
Heparin acts as a powerful physiological anticoagulant by activating antithrombin III.
Heparin acts as a powerful physiological anticoagulant by activating antithrombin III.
83. In an ECG, prolongation of the P-R interval indicates:
Correct Answer: B (Delayed AV nodal conduction (AV Heart Block))
P-R interval represents conduction time from SA node to ventricles; its prolongation indicates AV node blockage.
P-R interval represents conduction time from SA node to ventricles; its prolongation indicates AV node blockage.
84. The fibrous structural bands running through the interventricular septum are:
Correct Answer: B (Bundle of His (AV Bundle branches))
The Bundle of His descends through the interventricular septum before splitting into left and right branches.
The Bundle of His descends through the interventricular septum before splitting into left and right branches.
85. The conversion of soluble fibrinogen into insoluble fibrin polymer is catalyzed by:
Correct Answer: A (Thrombin)
Active thrombin enzymatically cleaves fibrinogen to produce insoluble fibrin meshworks that trap blood cells.
Active thrombin enzymatically cleaves fibrinogen to produce insoluble fibrin meshworks that trap blood cells.
86. Cardiac muscle cells receive their primary nutritional blood flow during which cardiac phase?
Correct Answer: B (Ventricular Diastole)
During systole, compressed myocardial microvasculature impedes flow; coronary perfusion occurs primarily during diastole.
During systole, compressed myocardial microvasculature impedes flow; coronary perfusion occurs primarily during diastole.
87. A sudden, complete cessation of effective mechanical pumping by the heart is termed:
Correct Answer: C (Cardiac arrest)
Cardiac arrest occurs when the heart completely stops beating and abruptly halts systemic circulation.
Cardiac arrest occurs when the heart completely stops beating and abruptly halts systemic circulation.
88. An aggregation of platelets and fibrin forming an intravascular clot is known as a:
Correct Answer: A (Thrombus)
A stationary pathological clot attached to an intact vessel wall is a thrombus (if detached and traveling, an embolus).
A stationary pathological clot attached to an intact vessel wall is a thrombus (if detached and traveling, an embolus).
89. The enzyme that dissolves fibrin clots during fibrinolysis is:
Correct Answer: B (Plasmin (Fibrinolysin))
Plasmin breaks down fibrin meshes into soluble degradation products to recanalize healed vessels.
Plasmin breaks down fibrin meshes into soluble degradation products to recanalize healed vessels.
90. Baroreceptors that monitor arterial blood pressure stretch are located in the:
Correct Answer: A (Carotid sinus and Aortic arch)
Carotid sinus and aortic arch baroreceptors relay stretch signals to the medulla to regulate vascular tone and heart rate.
Carotid sinus and aortic arch baroreceptors relay stretch signals to the medulla to regulate vascular tone and heart rate.
91. How many molecules of oxygen ($O_2$) can one molecule of fully saturated hemoglobin bind?
Correct Answer: B (4)
Each hemoglobin tetramer contains four iron-bearing heme groups, binding a maximum of 4 $O_2$ molecules (8 oxygen atoms).
Each hemoglobin tetramer contains four iron-bearing heme groups, binding a maximum of 4 $O_2$ molecules (8 oxygen atoms).
92. Incomplete double circulation (three-chambered heart) is found in:
Correct Answer: C (Amphibians and non-crocodilian Reptiles)
Amphibians and reptiles have two atria and one ventricle, leading to mixing of oxygenated and deoxygenated blood.
Amphibians and reptiles have two atria and one ventricle, leading to mixing of oxygenated and deoxygenated blood.
93. What is the normal fraction of blood volume occupied by RBCs (Hematocrit/PCV)?
Correct Answer: B (40 – 45%)
Packed Cell Volume (PCV) / Hematocrit averages 40–45% in healthy adult humans.
Packed Cell Volume (PCV) / Hematocrit averages 40–45% in healthy adult humans.
94. The innermost serous layer directly adhering to the surface of the myocardium is the:
Correct Answer: B (Epicardium (Visceral pericardium))
The epicardium (visceral layer of serous pericardium) tightly covers the outer muscular surface of the heart.
The epicardium (visceral layer of serous pericardium) tightly covers the outer muscular surface of the heart.
95. The muscular ridges lining the anterior interior walls of the atria are:
Correct Answer: B (Musculi pectinati (Pectinate muscles))
Pectinate muscles are prominent parallel muscular ridges found on the inner anterior surfaces of right and left atria.
Pectinate muscles are prominent parallel muscular ridges found on the inner anterior surfaces of right and left atria.
96. Which formed elements lack nuclei at structural maturity in humans?
Correct Answer: C (Both Erythrocytes and Platelets)
Mature human erythrocytes lose their nuclei during development, and platelets are non-nucleated cytoplasmic cell fragments.
Mature human erythrocytes lose their nuclei during development, and platelets are non-nucleated cytoplasmic cell fragments.
97. The muscular wall separating the left and right ventricles is called the:
Correct Answer: B (Interventricular septum)
A thick, muscular interventricular septum prevents oxygenated and deoxygenated blood from mixing between ventricles.
A thick, muscular interventricular septum prevents oxygenated and deoxygenated blood from mixing between ventricles.
98. Adrenal medullary hormones (epinephrine and norepinephrine) affect cardiac function by:
Correct Answer: A (Increasing heart rate and cardiac output)
Circulating catecholamines stimulate beta-1 adrenergic receptors, increasing heart rate, conduction velocity, and contractility.
Circulating catecholamines stimulate beta-1 adrenergic receptors, increasing heart rate, conduction velocity, and contractility.
99. An elevation of the ST segment on an ECG tracing is a classic clinical indicator of:
Correct Answer: C (Acute Myocardial Infarction (STEMI))
ST-segment elevation indicates acute transmural myocardial injury and ongoing myocardial infarction.
ST-segment elevation indicates acute transmural myocardial injury and ongoing myocardial infarction.
100. The right lymphatic duct drains lymph from the right upper quadrant directly into the:
Correct Answer: C (Right subclavian vein)
Lymph returns to the cardiovascular system through junctions at the subclavian veins (right lymphatic duct and thoracic duct).
Lymph returns to the cardiovascular system through junctions at the subclavian veins (right lymphatic duct and thoracic duct).