CoursesHistologyBody systemsLymphoid systemSpleen

Spleen

Learning objectives

After completing this study unit you will be able to:

Explain the histological division of the spleen.
Understand the microcirculation of the spleen.
Describe the characteristics of the red and white pulp in the spleen and identify these in histological images.

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The spleen is the largest lymphoid organ in the human body and plays an important role in immune defense and the filtration of old and damaged erythrocytes. It is divided into the red pulp and white pulp. Its outer surface is surrounded by a tough capsule from which trabeculae extend into the parenchyma of the spleen.

The spleen has both a closed and open blood circulation. Blood from the splenic artery enters the hilum and divides into branches via trabecular arteries, central arteries and brush arterioles up to the capillaries. In open circulation, the capillaries end in the reticular connective tissue. In closed circulation, the blood flows back into the splenic vein via the splenic sinuses, pulp veins and trabecular veins.

The red pulp is rich in blood and consists of pulp strands of reticular cells and numerous venous splenic sinusoids. There are also many macrophages in the pulp cords that phagocytize old erythrocytes. The white pulp represents the lymphatic tissue of the spleen. It is composed of lymph follicles and the periarterial lymphatic sheaths (PALS) around the central artery. The PALS are found only in the spleen and represent the T-zone of the organ, while the lymph follicles are the B-zone. The red and white pulp are separated from each other by the marginal zone.