Part 4 — Circulatory & Cardiovascular System (Questions 76–100)

Part 4 — Circulatory & Cardiovascular System (Questions 76–100)

76. The frog heart typically has how many chambers?
    A. Two-chambered (one atrium, one ventricle)
    B. Three-chambered (two auricles/atria and one ventricle)
    C. Four-chambered (two atria and two ventricles)
    D. Single-chambered sac
    Answer: B — Three-chambered (two auricles/atria and one ventricle).
    Explanations:
    A: Incorrect — two-chamber heart is fish type.
    B: Correct — adult frog heart has two atria and one ventricle.
    C: Incorrect — mammals/birds have four-chambered hearts.
    D: Incorrect — not a true heart structure.

77. In the frog heart, the mixing of oxygenated and deoxygenated blood is minimised by:
    A. Complete septum dividing the ventricle into two chambers
    B. Functional separation by timing of contractions, trabeculae and spiral valve in conus arteriosus/ventricle morphology
    C. Valves between atria and ventricle that prevent any mixing
    D. Presence of two ventricles segregating blood fully
    Answer: B — Functional separation by timing of contractions, trabeculae and spiral valve in conus arteriosus/ventricle morphology.
    Explanations:
    A: Incorrect — no complete septum in ventricle.
    B: Correct — ventricular trabeculae and timing and conus arteriosus spiral fold help direct oxygenated and deoxygenated streams separately.
    C: Incorrect — atrioventricular valves exist but do not fully prevent mixing; functional separation is achieved differently.
    D: Incorrect — only one ventricle present.

78. Oxygenated blood from lungs returns to the frog heart via:
    A. Pulmonary veins to the left atrium (auricle)
    B. Pulmonary arteries to the ventricle directly
    C. Renal veins into right atrium
    D. Hepatic portal vein
    Answer: A — Pulmonary veins to the left atrium (auricle).
    Explanations:
    A: Correct — oxygenated blood from lungs returns via pulmonary veins into left atrium.
    B: Incorrect — arteries carry blood away from heart to lungs, not back.
    C: Incorrect — renal veins drain kidneys.
    D: Incorrect — hepatic portal is venous drainage from gut to liver.

79. The main artery that arises from the heart and distributes oxygenated blood to the body in frog is:
    A. Carotid artery and systemic arches via truncus arteriosus/conus arteriosus divisions
    B. Umbilical artery only
    C. Hepatic duct
    D. Dorsal aorta directly from ventricle with branching via truncus arteriosus
    Answer: D — Dorsal aorta directly from ventricle with branching via truncus arteriosus.
    Explanations:
    A: Partially correct but incomplete — carotids are branches; the major pathway involves truncus arteriosus dividing into systemic arches and dorsal aorta.
    B: Incorrect — umbilical vessels are embryonic in placentals, not main.
    C: Incorrect — hepatic duct is biliary.
    D: Correct — from ventricle blood enters conus/truncus arteriosus which divides to arches and dorsal aorta supplying body.

80. The cavity that receives deoxygenated blood from the systemic circulation in frog is:
    A. Left atrium
    B. Right atrium (auricle)
    C. Single ventricle only
    D. Cloaca
    Answer: B — Right atrium (auricle).
    Explanations:
    A: Incorrect — left atrium receives oxygenated blood from lungs.
    B: Correct — systemic (venous) blood returns to the right atrium.
    C: Incorrect — ventricle receives blood from both atria but right atrium is primary reservoir for deoxygenated blood.
    D: Incorrect — cloaca is digestive/urogenital outlet.

81. Which of the following statements about frog blood is correct?
    A. Frog RBCs are non-nucleated like mammals
    B. Frog RBCs are nucleated and oval in shape
    C. Frog blood lacks hemoglobin
    D. Frog blood cells are identical to fish cartilage cells
    Answer: B — Frog RBCs are nucleated and oval in shape.
    Explanations:
    A: Incorrect — amphibian RBCs retain nucleus (unlike mammalian RBCs).
    B: Correct — amphibians have nucleated red blood cells.
    C: Incorrect — frogs have hemoglobin in RBCs for oxygen transport.
    D: Incorrect — RBCs are blood cells, not cartilage cells.

82. The contraction phase of the heart is called:
    A. Diastole
    B. Systole
    C. Peristole
    D. Apnoea
    Answer: B — Systole.
    Explanations:
    A: Incorrect — diastole is relaxation/filling.
    B: Correct — systole = contraction pumping blood.
    C: Incorrect — peristole not a standard cardiac term.
    D: Incorrect — apnoea is cessation of breathing.

83. The frog’s coronary circulation supplies:
    A. Oxygenated blood to heart muscles via coronary arteries from systemic arches
    B. Oxygen directly from buccal cavity to heart muscle
    C. Heart has no blood vessels for its own nutrition
    D. Only venous blood supplies the heart
    Answer: A — Oxygenated blood to heart muscles via coronary arteries from systemic arches.
    Explanations:
    A: Correct — coronary vessels supply myocardium with oxygenated blood.
    B: Incorrect — buccal cavity doesn’t directly supply the myocardium.
    C: Incorrect — heart has its own blood supply.
    D: Incorrect — arterial blood supplies heart tissue.

84. Which vessel collects blood from liver and drains into the sinus venosus in vertebrates including amphibians?
    A. Hepatic portal vein collecting from gut to liver, hepatic veins drain liver to heart
    B. Pulmonary vein
    C. Renal artery
    D. Carotid artery
    Answer: A — Hepatic portal vein collecting from gut to liver, hepatic veins drain liver to heart.
    Explanations:
    A: Correct — hepatic portal brings nutrient-rich blood to liver; hepatic veins return blood toward sinus venosus/right atrium region.
    B: Incorrect — pulmonary veins bring oxygenated blood from lungs.
    C: Incorrect — renal artery supplies kidney.
    D: Incorrect — carotid artery supplies head.

85. Where is the sinoatrial (SA) and atrioventricular (AV) nodal-like pacemaker located in amphibian heart?
    A. Sinus venosus near venous inflow acts as pacemaker region; AV region near atrioventricular canal coordinates delay.
    B. In the cloaca only
    C. Entire heart contracts uniformly with no pacemaker
    D. Pacemaker in lungs
    Answer: A — Sinus venosus near venous inflow acts as pacemaker region; AV region near atrioventricular canal coordinates delay.
    Explanations:
    A: Correct — sinus venosus acts like pacemaker initiating contraction; AV region provides conduction delay.
    B: Incorrect — cloaca unrelated.
    C: Incorrect — hearts have pacemaker regions for coordinated contraction.
    D: Incorrect — lungs not pacemaker.

86. The functional significance of the three-chambered heart in frog is:
    A. To fully separate oxygenated and deoxygenated blood like mammals
    B. To allow partial separation and distribution of blood to pulmonary/cutaneous and systemic circuits suitable for amphibian lifestyle
    C. To serve as food storage organ
    D. To reduce blood flow to limbs only
    Answer: B — To allow partial separation and distribution of blood to pulmonary/cutaneous and systemic circuits suitable for amphibian lifestyle.
    Explanations:
    A: Incorrect — not full separation; partial functional segregation exists.
    B: Correct — mixing is minimized but not eliminated; amphibians benefit from cutaneous respiration and variable circulation.
    C: Incorrect — heart not for storage.
    D: Incorrect — not specific to limbs.

87. The major venous channel returning blood from hindlimbs and pelvic region in frog is:
    A. Femoral vein to posterior vena cava (or sinus venosus region)
    B. Carotid artery
    C. Hepatic artery
    D. Pulmonary artery
    Answer: A — Femoral vein to posterior vena cava (or sinus venosus region).
    Explanations:
    A: Correct — venous return from posterior limbs travels through femoral and pelvic veins into systemic venous return to heart.
    B: Incorrect — carotid is arterial supply to head.
    C: Incorrect — hepatic artery is arterial supply to liver.
    D: Incorrect — pulmonary artery carries blood to lungs.

88. Cutaneous respiration in frog significantly affects circulatory physiology by:
    A. Allowing gas exchange through skin and thus altering distribution of blood oxygenation before returning to heart
    B. Blocking all blood oxygenation requiring lungs only
    C. Stopping heart function during swimming
    D. Turning blood into lymph fluid
    Answer: A — Allowing gas exchange through skin and thus altering distribution of blood oxygenation before returning to heart.
    Explanations:
    A: Correct — skin respiration supplies oxygen directly to blood in cutaneous vessels, which affects overall oxygenation and reduces reliance on lungs.
    B: Incorrect — lungs complement skin respiration.
    C: Incorrect — heart continues functioning.
    D: Incorrect — blood remains blood.

89. The conus arteriosus in frog heart contains a spiral valve which:
    A. Separates pulmonary and systemic outflow to some extent directing blood streams
    B. Prevents blood from entering the ventricle
    C. Produces hormones for blood pressure regulation
    D. Is purely vestigial with no function
    Answer: A — Separates pulmonary and systemic outflow to some extent directing blood streams.
    Explanations:
    A: Correct — spiral fold in conus helps direct oxygen-rich blood to systemic arches and deoxygenated to pulmocutaneous circuit.
    B: Incorrect — it doesn’t prevent ventricular filling.
    C: Incorrect — no hormonal function.
    D: Incorrect — functional in directing flow.

90. Which of the following statements about amphibian blood circulation is true?
    A. There is a closed circulatory system with heart, arteries, capillaries and veins
    B. Blood flows openly into body cavity like open circulatory systems
    C. Frog blood lacks capillaries entirely
    D. Circulation in frogs is identical to arthropods
    Answer: A — There is a closed circulatory system with heart, arteries, capillaries and veins.
    Explanations:
    A: Correct — amphibians have a closed circulatory system typical of vertebrates.
    B: Incorrect — open circulation occurs in many arthropods, not frogs.
    C: Incorrect — capillaries are present in tissues.
    D: Incorrect — fundamental differences exist.

91. Which chamber of the frog heart receives oxygenated blood from the lungs and skin?
    A. Right atrium
    B. Left atrium
    C. Single ventricle only
    D. Sinus venosus
    Answer: B — Left atrium.
    Explanations:
    A: Incorrect — right atrium receives deoxygenated systemic blood.
    B: Correct — pulmonary/pulmocutaneous veins drain oxygenated blood to left atrium.
    C: Incorrect — ventricle receives blood from both atria but left atrium is the immediate receiver.
    D: Incorrect — sinus venosus is venous collecting chamber into atria.

92. Which is the correct sequence of blood flow from ventricle to systemic circulation in frog?
    A. Ventricle → conus arteriosus/truncus arteriosus → arterial arches → dorsal aorta → systemic capillaries
    B. Ventricle → pulmonary veins → lungs → systemic arteries
    C. Ventricle → atria → lungs → capillaries
    D. Ventricle → cloaca → intestine → aorta
    Answer: A — Ventricle → conus arteriosus/truncus arteriosus → arterial arches → dorsal aorta → systemic capillaries.
    Explanations:
    A: Correct — ventricle pumps into conus/truncus which divides into arches and dorsal aorta supplying body.
    B: Incorrect — pulmonary veins return blood to heart; flow direction incorrect.
    C: Incorrect — ventricles do not pump into atria.
    D: Incorrect — cloaca and intestine are not direct arterial paths.

93. The sinus venosus in amphibian heart functions to:
    A. Collect venous blood and coordinate heart rhythm before atrial contraction
    B. Pump blood into dorsal aorta forcefully like ventricle
    C. Store food temporarily
    D. Produce digestive enzymes
    Answer: A — Collect venous blood and coordinate heart rhythm before atrial contraction.
    Explanations:
    A: Correct — the sinus venosus receives venous return and has pacemaker function in amphibians.
    B: Incorrect — not a major pumping chamber like ventricle.
    C: Incorrect — unrelated to digestion.
    D: Incorrect — not secretory organ.

94. The main difference between amphibian and mammalian heart is:
    A. Amphibians have 3-chambered heart with mixing; mammals have 4-chambered heart with complete separation of systemic/pulmonary circuits
    B. Amphibians have four chambers while mammals have three
    C. Amphibians have no blood while mammals have blood
    D. There is no difference
    Answer: A — Amphibians have 3-chambered heart with mixing; mammals have 4-chambered heart with complete separation of systemic/pulmonary circuits.
    Explanations:
    A: Correct — three-chambered vs four-chambered arrangement is key circulatory difference.
    B: Incorrect — reverse statement.
    C: Incorrect — both have blood.
    D: Incorrect — substantial differences exist.

95. Which of the following vessels brings oxygenated blood back to the heart from lungs?
    A. Pulmonary veins into left atrium
    B. Pulmonary artery into ventricle
    C. Dorsal aorta into right atrium
    D. Hepatic portal vein into sinus venosus
    Answer: A — Pulmonary veins into left atrium.
    Explanations:
    A: Correct — pulmonary veins return oxygenated blood from lungs to left atrium.
    B: Incorrect — pulmonary arteries carry deoxygenated blood to lungs.
    C: Incorrect — dorsal aorta carries arterial blood away from heart.
    D: Incorrect — hepatic portal vein drains gut to liver.

96. Which adaptation allows frogs to vary relative blood flow to lungs vs. skin?
    A. Presence of valves and branching architecture in truncus arteriosus and ability to constrict branches, enabling routing more to lungs or skin depending on activity and respiratory need
    B. Complete separation like mammals so cannot vary flow
    C. No vascular control exists; flow fixed
    D. Only lymphatics control flow, not arteries
    Answer: A — Presence of valves and branching architecture in truncus arteriosus and ability to constrict branches, enabling routing more to lungs or skin depending on activity and respiratory need.
    Explanations:
    A: Correct — amphibians can adjust blood distribution between pulmonary, cutaneous and systemic circuits.
    B: Incorrect — mammals are less able to shunt similarly.
    C: Incorrect — vascular control present.
    D: Incorrect — lymphatics not primary regulator of arterial blood flow.

97. Which is true about frog’s blood pressure relative to mammals?
    A. Higher than mammals due to single ventricle
    B. Generally lower systemic blood pressure reflecting intermittent pulmonary/cutaneous respiration and less separation of circuits
    C. Identical to mammals in all respects
    D. Zero because frog heart doesn’t pump blood
    Answer: B — Generally lower systemic blood pressure reflecting intermittent pulmonary/cutaneous respiration and less separation of circuits.
    Explanations:
    A: Incorrect — three-chambered heart and partial mixing usually produces lower pressure.
    B: Correct — amphibians tend to have lower systemic pressures compared to endothermic mammals.
    C: Incorrect — physiological differences lead to different pressures.
    D: Incorrect — frog heart does pump blood.

98. Venous blood from the head region reaches the heart via:
    A. Jugular veins draining into sinus venosus/right atrium
    B. Pulmonary arteries carrying blood to lungs
    C. Carotid artery into left atrium
    D. Afferent renal vein into cloaca
    Answer: A — Jugular veins draining into sinus venosus/right atrium.
    Explanations:
    A: Correct — jugular veins return head venous blood towards sinus venosus/atriac inlet.
    B: Incorrect — pulmonary arteries go to lungs away from heart.
    C: Incorrect — carotid are arteries, not veins.
    D: Incorrect — afferent renal veins not correct path.

99. In frogs, oxygen-rich blood distributed to tissues is supplied mainly by which arterial trunk?
    A. Dorsal aorta branches after systemic arch divisions (carotid, systemic arches)
    B. Umbilical artery only
    C. Renal portal does all oxygen delivery
    D. Hepatic portal to heart only
    Answer: A — Dorsal aorta branches after systemic arch divisions (carotid, systemic arches).
    Explanations:
    A: Correct — dorsal aorta and its branches supply tissues with oxygenated blood.
    B: Incorrect — umbilical arteries are embryonic/placental in mammals; frogs don’t rely on them.
    C: Incorrect — renal portal is venous/venous-shunt system in amphibians mainly for kidneys.
    D: Incorrect — hepatic portal carries nutrient-rich blood to liver, not main systemic arterial supply.

100. Which of the following statements about renal portal circulation in amphibians is correct?
     A. Renal portal system can direct venous blood from hindlimbs through kidneys affecting filtration; it’s an additional venous routing not present in mammals in same way
     B. It is the primary arterial supply to the brain
     C. It returns oxygenated blood from lungs to the heart
     D. It is absent in amphibians
     Answer: A — Renal portal system can direct venous blood from hindlimbs through kidneys affecting filtration; it’s an additional venous routing not present in mammals in same way.
     Explanations:
     A: Correct — renal portal system channels blood from posterior parts through kidneys before joining systemic venous return; significant in amphibians.
     B: Incorrect — renal portal not arterial to brain.
     C: Incorrect — not related to lungs.
     D: Incorrect — it is present in amphibians and many reptiles.

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