**Question:** All of the following are the components of the white pulp of spleen, except -

A. Periarteriolar lymphoid sheath (PALS)
B. Red pulp
C. Splenic sinusoids
D. Arteries and veins

**Core Concept:**
The spleen is an essential immune organ that plays a vital role in blood purification, immune response, and storage. The spleen is divided into two main areas - the red pulp and the white pulp. The white pulp is further subdivided into various components.

**Why the Correct Answer is Right:**
The correct answer is D - arteries and veins, because arteries and veins are the blood vessels that carry blood through the spleen, not components of the white pulp. The white pulp consists of specialized lymphoid tissue, including the periarteriolar lymphoid sheath (PALS), which surrounds the splenic arteries, and the T-cells and B-cells that reside within it.

**Why Each Wrong Option is Incorrect:**

A. Periarteriolar lymphoid sheath (PALS) is a crucial component of the white pulp, providing a niche for naïve T-cells to differentiate into effector T-cells and memory T-cells. This is why option A is incorrect.

B. Red pulp is the other main component of the spleen, responsible for trapping and eliminating pathogens, dead red blood cells, and other particles from the blood. This is why option B is incorrect.

C. Splenic sinusoids are blood vessels that carry blood through the spleen, particularly in the red pulp, not the white pulp. This is why option C is incorrect.

**Correct Answer:**

**Correct Answer: D (Arteries and Veins)**

**Clinical Pearl:**

The spleen is an essential organ in the immune system, helping to filter blood, facilitate immune response, and store red blood cells. Understanding the anatomical structure and function of spleen components, like the white pulp and red pulp, is crucial for understanding the spleen's roles in the immune system and blood filtration.