Body Fluids and Circulation (MCQs)

Correct Answer: (a)
Contraction of arteriole smooth muscle causes vasoconstriction, narrowing the lumen and increasing resistance to blood flow. It generally reduces, rather than increases, blood flow to an organ and decreases heat loss through the skin.

Correct Answer: (c)
Both systems contain capillaries that facilitate exchange with tissues. However, the lymphatic system does not have arteries and is not a closed system; it drains lymph unidirectionally toward the heart.

Correct Answer: (a)
Not all arteries carry oxygenated blood (e.g., pulmonary arteries carry deoxygenated blood), and not all veins carry deoxygenated blood (pulmonary veins carry oxygenated blood). The other statements correctly describe vascular structure and regulation.

Correct Answer: (b)
The sinoatrial (SA) node is the natural pacemaker of the heart. Its spontaneous depolarization initiates the electrical impulse that causes atrial systole, followed by ventricular systole. Therefore, systole begins with activation of the SA node.

Correct Answer: (a)
An electrocardiogram (ECG) records the electrical activity of the heart by detecting changes in electrical potential produced during depolarization and repolarization of cardiac muscle fibers throughout the cardiac cycle. It does not measure ion concentration, force of contraction, or blood volume directly.

Correct Answer: (c)
Blood flows away from the heart through arteries, then arterioles, reaches capillaries for exchange, and returns via venules and veins back to the heart. The lymphatic system is separate and not part of the direct blood circulation sequence.

Correct Answer: (b)
CO₂ produced in the left ventricle enters the coronary circulation, returns to the right atrium, then passes through the right ventricle and lungs before being exhaled. It does not re-enter the left atrium before leaving the body.

Correct Answer: (a)
Blood clots consist primarily of fibrin, an insoluble protein formed from fibrinogen during the clotting cascade. Prothrombin is a clotting factor but is not a structural component of the clot itself.

Correct Answer: (d)
All listed pairings are correct: erythrocytes transport oxygen via hemoglobin, platelets function in clotting, and plasma transports wastes, nutrients, and hormones. Therefore, none of the pairings is incorrect.

Correct Answer: (c)
Amphibians have a three-chambered heart with a single ventricle, but internal ridges and channels partially separate oxygenated and deoxygenated blood, reducing mixing. Mammals, in contrast, have complete separation with a four-chambered heart.

Correct Answer: (a)
Electrical conduction begins at the SA node in the atria, spreads across atrial tissue, then passes to the AV node. From there, the impulse travels through the bundle of His and Purkinje fibers to the apex of the ventricles, ensuring contraction from the bottom upward for efficient blood ejection.

Correct Answer: (c)
When cuff pressure exceeds the maximum (systolic) arterial pressure, the artery is completely occluded and blood flow stops. As cuff pressure decreases below systolic pressure, blood flow resumes, producing audible pulses.