Chapter 479 Anatomy and Function of the Spleen
Anatomy
The splenic precursor is recognizable by 5 wk of gestation. At birth, the spleen weighs approximately 11 g. Thereafter, it enlarges until puberty, reaching an average weight of 135 g, and then diminishes in size during adulthood. Approximately 15% of patients will have an accessory spleen. The major splenic components are a lymphoid compartment (white pulp) and a filtering system (red pulp). The white pulp consists of periarterial lymphatic sheaths of T lymphocytes with embedded germinal centers containing B lymphocytes. The red pulp has a skeleton of fixed reticular cells, mobile macrophages, partially collapsed endothelial passages (cords of Billroth), and splenic sinuses. A marginal zone rich in dendritic (antigen-presenting) cells separates the red pulp from the white pulp. The splenic capsule contains smooth muscle and contracts in response to epinephrine. Approximately 10% of the blood delivered to the spleen flows rapidly through a closed vascular network. The other 90% flows more slowly through an open system (the splenic cords), where it is filtered through 1-5 µm slits before entering the splenic sinuses.

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