Survey of spleen (human)

Stain: Azan. The spleen is covered by a capsule (1) of dense connective tissue and elastic fibers. The capsule continues into the spleen as trabeculae (2) carrying blood vessels and nerve fibers. As arteries leave the trabeculae it becomes invested by a sheath of T cells forming a PALS (3) or periarteriolar lymphatic sheath to which B cell follicles are joined and all together are called the white pulp (4). The red pulp (5) consists of sinusoids (white open lumen) surrounded by splenic cords (Billroth). The blood is drained towards pulp veins and trabecular veins. In several mammalians the connective tissue contains many myofibroblasts (note: with increasing physical stress contraction causes rapid expulsion of blood into the general circulation)