Production of red blood cells in a mature adult occurs in all the following areas except the:

Correct Answer: B

Rationale: In adults, RBC production (erythropoiesis) occurs in red bone marrow of flat bones (sternum, skull, vertebrae) and proximal ends of long bones. The femur’s shaft in adults is mostly yellow marrow, not active in erythropoiesis.

Correct Answer: A

Rationale: The EKG shows inverted T-waves, a hallmark of hypokalemia (low potassium, A), which affects repolarization. Calcium (B) impacts rate/contractility, not T-waves, and chloride (C) and sodium (D) abnormalities don’t typically cause this pattern. (Source: Document, p. 10-11; assumes image context)

Correct Answer: D

Rationale: Cardiac output (CO, D) is the volume of blood ejected by the heart per minute (CO = HR × SV, ~5 L/min at rest). EDV (A) is pre-contraction volume, SV (B) is per beat, HR (C) is beats per minute, and BP (E) is pressure, not volume.

Correct Answer: B

Rationale: The first heart sound (S₁, ‘lub’) occurs when AV valves (tricuspid, mitral) close at the start of ventricular systole (B). Semilunar valve closure (A) is S₂ (‘dub’), and atrial contraction (C) precedes S₁, not causing it.

Correct Answer: C

Rationale: Fibrillation (C) is rapid, uncoordinated beating (e.g., atrial or ventricular). Heart block (A) is conduction failure, tachycardia (B) is fast but coordinated, and bradycardia (D) is slow.