Resistive vessels of the circulatory system are:

Correct Answer: C

Rationale: Small arteries and arterioles are the primary resistive vessels because their narrow lumens and muscular walls (tunica media) allow them to regulate blood flow and peripheral resistance through vasoconstriction and vasodilation.

Correct Answer: B

Rationale: The S₂ heart sound ('dub') is produced by the closure of the aortic and pulmonic valves. A murmur at S₂ suggests impairment of one of these, most likely the aortic valve, as it’s more commonly affected in adults (e.g., stenosis). Tricuspid and mitral (bicuspid) closure produces S₁. (Source: Document, p. 62, Valve sounds)

Correct Answer: C

Rationale: Calcium ions are essential in the clotting cascade, particularly for converting prothrombin to thrombin (via factor Xa). They also aid other steps but are not directly needed to form fibrinogen, thromboplastin, or prothrombin.

Correct Answer: B

Rationale: IgE is primarily involved in allergic reactions and parasitic infections, binding to mast cells and basophils to release histamine. IgG protects newborns via placental transfer, IgA protects mucosal areas, and IgM fights bacteria.

Correct Answer: A

Rationale: Hemophilia A is a deficiency in factor VIII (antihemophilic factor), impairing the intrinsic pathway. Factor IX deficiency is hemophilia B, and VII and XII are unrelated to hemophilia A.