Spleen histology

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Spleen histology

USMLE® Step 1 questions

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USMLE® Step 1 style questions USMLE

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A researcher is studying the histology of the spleen and the different types of cells and structures found in it. A biopsy is taken from a spleen and is examined under a microscope, as shown below. Which of the following best describes area A?


The lymphatic system is an essential part of the immune system and it consists of a network of lymphatic vessels, tissues, and organs.

The lymphatic vessels drain interstitial fluid or lymph from peripheral tissues back into the blood.

Lymphoid tissue and organs contain a lot of lymphocytes and other white blood cells.

The primary lymphoid organs include the thymus and bone marrow.

And the secondary lymphoid organs include the tonsils, lymph nodes, spleen and mucosa-associated lymphoid tissue or MALT for short.

The spleen is the largest lymphoid organ.

It receives blood from the splenic artery and is the only lymphoid organ that primarily filters blood instead of lymph.

It’s an encapsulated organ that’s typically about 12 cm in length, 7 cm wide, and 3 cm deep.

The spleen’s functional tissue or parenchyma consists of red pulp, with small white nodules of lymphatic tissue scattered throughout called the white pulp.

Although, when looking at the spleen histologically after it’s been stained with H&E, the red pulp is actually stained a combination of pink and purple; and the white pulp is stained dark purple because it contains a large number of basophilic nuclei.

If we take a closer look at the outer edge of the spleen, the capsule that surrounds the spleen is seen as a dense layer of pink connective tissue.

The connective tissue also forms short extensions into the spleen called trabeculae.

The trabeculae will also occasionally surround arteries as they enter the parenchyma of the spleen.

These trabecular arteries are branches of the splenic artery.

The remainder of the tissue seen in this image is the highly vascular red pulp.


The spleen is an essential part of the immune system, which is also responsible for filtering blood and removing damaged or old red blood cells. At a gross level, the spleen's parenchyma consists of red pulp, with small white nodules of lymphatic tissue scattered throughout called the white pulp. The red pulp has sinusoids, splenic cords, and macrophages, and plays a major role in removing old and damaged red blood cells.

The white pulp, which is involved in immune function, is arranged in spherical nodules called splenic nodules surrounded by a sheath of lymphoid tissue known as the periarteriolar lymphoid sheath (PALS). Within the splenic nodules are two types of lymphoid tissue: the follicles and the marginal zone. The follicles contain B-lymphocytes, whereas the marginal zone contains a mixture of B-lymphocytes, T-lymphocytes, and macrophages.


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