AB2.H2.2 +D1 Spleen
Spleen:
- The spleen is located in the left hypochondrium of the abdominal cavity
- The spleen is a large lymphoid organ which is usually described as having the size and shape of a clenched fist
- Its main immune function is to monitor the blood for pathogens
- However, it also plays an important role in filtering the blood for debris, in removal of effete red blood cells and as a store for blood cells
- The spleen has a connective tissue capsule
- The capsule contains smooth muscle
- This may contract to force blood, stored in the spleen, into the general circulation
- Connective tissue septae arise from the capsule and pass internally to support the spleen and its major blood vessels
- Between the septae, the spleen is divided into red pulp and white pulp, both of which contain blood/immune cells supported by a connective tissue framework
- White pulp is the name given to the lymphoid tissue which forms a collar around the arterioles that penetrate the substance of the spleen
- The red pulp is the name given to the area of the spleen which contains the full range of peripheral blood cells
- It is in this part of the spleen that effete red blood cells, and other cellular debris in the blood, are removed
- Part of the red pulp is a store of blood cells and platelets
- At the boundaries between the white pulp and the red pulp lies an ill-defined zone known as the marginal zone
- In this zone, macrophages are abundant
- They filter the blood of particulate material as well as act as antigen presenting cells to support the immune function of the spleen
Questions:
Micrograph of Spleen:
- This micrograph of spleen shows how densely packed with red and white blood cells the spleen is
- This histological section was prepared from a spleen from an animal which had received an intravenous injection of indian ink (carbon particles)
- The carbon particles in the ink have been endocytosed by macrophages
- Although (black) macrophages can be seen in both the white pulp and the red pulp areas there is a distinct concentration of them at the junction between the white and red pulp
- These areas of the spleen are known as marginal zones
- In the marginal zone, open ended blood vessels release blood (plasma and cells) into the spleen matrix
- Macrophages in this zone monitor the blood for foreign antigen
W = area of white pulp containing predominantly white blood cells
R = area of red pulp which contains predominantly red blood cells
