Splenic sheathed capillaries (human)

Stain: Azan. The blood flow in the spleen goes from splenic artery to trabecular artery to central or follicular artery (with a periarteriolar lymphatic sheath or PALS), and upon leaving the follicle the blood flows through penicillar arterioles and sheathed capillaries and terminal arterial capillaries to the splenic sinusoids, and back to veins of the pulp and the splenic veins. Upon exiting the white pulp the arterial capillaries are surrounded by a sheath of phagocytotic cells and reticular fibres. 1. sheathed capillary (cross-sectioned); 2. sheathed capillary (longitudinal sectioned); 3. sinusoid; 4. accumulation of macrophages surrounding sheathed capillary; Note that 2+4 are embedded by splenic cord tissue. Background: Splenic cords (Billroth), these so-called cords or pulpar strands are composed of three-dimensional spongy-like meshworks of reticular cells/fibres with in between free circulating cells. Actually the splenic red pulp comprises all sinusoidal structures together with the intersinusoidal reticular meshworks/cells (= cords). The wall of the sinusoids is composed of elongated rod-like endothelial cells that are orientated parallel to each other in the long axis of the sinus. Depending on the section the shape of nuclei of the endothelial cells differs (arrows). Circumscribing reticular fibres reveal parallel to each other. These fibres consist of collagen type III with microfibrils and are enclosed by a glycoprotein coating. They surround and reinforce sinusoids.