A client is admitted with an occlusion (blockage) of the circumflex artery. When discussing the diagnosis with the client and family, the nurse would explain that this vessel is a branch of the:

Correct Answer: B

Rationale: The circumflex artery is a branch of the left coronary artery, which originates from the aorta. It supplies the left atrium and ventricle. Pulmonary veins and arteries relate to lung circulation, and the superior vena cava is a vein, not an artery.

Correct Answer: C

Rationale: IgA, found in mucosal secretions (e.g., saliva, tears), protects the GI, urogenital, and respiratory tracts against pathogens. IgM and IgG fight blood infections, and IgE is linked to allergies.

Correct Answer: D

Rationale: The sinoatrial (SA) node is the heart’s pacemaker because it has the highest intrinsic rate of spontaneous depolarization (~60-100 beats/min), outpacing other cardiac cells (e.g., AV node: 40-60, Purkinje: 20-40). While it generates impulses (C), D specifies the rate, which is key. Cholinergic (parasympathetic) innervation slows it, and sympathetic innervation enhances it, but neither defines its pacemaker role.

Correct Answer: C

Rationale: In complete heart block (third-degree), all impulses are blocked at the AV node (C), causing ventricles to beat independently at 20-40 bpm via Purkinje fibers, not 60 (A). The SA node functions normally (B is false), and BP is typically low (hypotension) due to bradycardia, not high (D). (Source: Document, p. 6-7)

Correct Answer: C

Rationale: An electrocardiogram (ECG, C) records the heart’s electrical activity via skin electrodes, showing rhythm and conduction. A (eye movement), B (brain activity), D (ultrasound imaging), and E (muscle activity) are unrelated to this function.