Thymus and Spleen

The Spleen: What is it good for?

1. Filters blood

2. Iron Retrieval

3. RBC reserve

4. Immune Response*

5. Fetal Hematopoiesis

The ‘White’ Pulp

• Appears basophilic on H&E and red on silver stain

• Site where immune response is mounted; formation of germinal centers

• Germinal centers with B cells and B cell derivatives push the ‘central artery’ off to the side

White Pulp Vasculature

• The central artery is found in the white pulp

• The central artery is surrounded by the PALS, which is T cells

• Penicilli branch from the central artery into the red pulp

White Pulp Vasculature

• The central artery is found in the white pulp

• The central artery is surrounded by the PALS, which is T cells

• Penicilli branch from the central artery into the red pulp

White Pulp Vasculature

• The central artery is found in the white pulp

• The central artery is surrounded by the PALS, which is T cells

• Penicilli branch from the central artery into the red pulp

Red Pulp Vasculature:

• Penicilli give rise to ellipsoids

• Ellipsoids are capillaries ensheathed by reticular cells and macrophages; their lumens are often occluded in histo sections

• Blood is filtered by macrophages through fenestrations in the sinusoids

Sinusoids

See how the basal lamina is interrupted; evident with both stains

Sinusoids

Lining of endothelial cells: apposed to one another, but remain separated

Macrophages extend their processes into the lumen of the sinusoid (you can see the remains of RBCs in macrophages)

The Red Pulp

• Appears Red on H&E

• Composed of sinusoids and Cords of Billroth

• The cords are the parenchyma of the red pulp; they are composed of reticular tissue w/ macrophages, red blood cells, and lymphocytes

Silver Stain

*Notice how reticular fibers are evident with silver stain and not H&E

*Notice the difference in appearance with the two different stains