Which type of intracellular signaling involves hormones that are released into the bloodstream to affect distant target cells?

Correct Answer: D

Rationale: Endocrine signaling uses hormones to target distant cells.

Correct Answer: D

Rationale: RBCs break down after ~120 days in the spleen (reticulo-endothelial system), yielding bilirubin transported by albumin to the liver; most iron is recycled.

Correct Answer: B

Rationale: Plasma specific gravity (~1.025) is primarily due to proteins (e.g., albumin), not electrolytes.

Correct Answer: C

Rationale: Thrombin (from prothrombin) cleaves fibrinogen, and fibrin monomers polymerize to form clots; heparin inhibits thrombin.

Correct Answer: A

Rationale: B12 absorption occurs in the ileum; deficiency causes megaloblastic anemia (large RBCs), not small.