Which of the following is true regarding the spleen?

A. the red pulp is made up of phagocytic cells
B. the white pulp is made up of phaocytic cells
C. the red pulp is clustered around capillaries
D. the white pulp is clustered around arterioles

To determine which of the given statements is true regarding the spleen, let's break down the options and find the correct answer.

A. The red pulp is made up of phagocytic cells.
To verify this, we need to understand the composition of the red pulp in the spleen. The red pulp contains a mixture of red blood cells, macrophages, and other immune cells. Macrophages are phagocytic cells that play a vital role in filtering old and damaged red blood cells. Therefore, Option A is true.

B. The white pulp is made up of phagocytic cells.
To determine if this statement is true or false, we need to uncover the constituents of white pulp. The white pulp of the spleen primarily consists of lymphocytes and other immune cells. It is responsible for the immune functions of the spleen, such as trapping pathogens and initiating immune responses. Phagocytic cells are mostly found in the red pulp, not in the white pulp. Hence, Option B is false.

C. The red pulp is clustered around capillaries.
To verify this statement, we need to understand the organization of the spleen's red pulp. The red pulp of the spleen consists of several splenic cords, which are regions rich in red blood cells, supported by reticular fibers and macrophages. These splenic cords are interspersed with vascular spaces called splenic sinuses. These sinuses are wider than capillaries and allow blood to flow slowly through the red pulp. Therefore, Option C is false.

D. The white pulp is clustered around arterioles.
To determine whether this statement is true or false, we need to understand the arrangement of the spleen's white pulp. The white pulp of the spleen is organized in small compartments known as lymphoid follicles. These follicles contain arterioles, which carry blood into the spleen. The arterioles branch off into specialized areas called the periarteriolar lymphoid sheaths (PALS). The PALS are rich in T lymphocytes and are an essential part of the immune response. Therefore, Option D is true.

In summary, the correct answer to the given question is:
A. The red pulp is made up of phagocytic cells.
D. The white pulp is clustered around arterioles.