Describe the histological structure and function of the thymus (ANAT2020 only).

Correct Answer: A

Rationale: The thymus is a primary lymphoid organ where T-cells mature through antigen-independent differentiation . It has a connective tissue capsule with trabeculae forming lobules , a cortex with densely packed thymocytes, and a medulla with Hassall's corpuscles (C, D), supported by epithelioreticular cells.

Correct Answer: D

Rationale: White pulp is round/oval, has four zones (including PALS), and a central arteriole.

Correct Answer: C

Rationale: Thymus has a dark cortex , pale medulla with Hassall's corpuscles (B, D); white/red pulp is spleen-specific (C is incorrect).

Correct Answer: B

Rationale: Splenic sinusoids are lined with elongated endothelial cells with large spaces ; Kupffer cells are in liver , stave cells line sinusoids (C is misphrased), basement membranes are discontinuous .

Correct Answer: C

Rationale: The Fc region (tail of heavy chains, C) binds Fc receptors on macrophages; Fab and antigen-binding parts bind antigens.