Hepatitis A

This causes endotheli-al cells to contract and separate from each other, exposing a naked basement membrane. Neutrophils stick to the exposed collagen and extravasate (i. e., move out into the connective tissue). Histamine also causes local arterioles to relax, affect ing a rise in venous pressure and increased leaking of fluid. This produces the classic signs of inflammation: redness, heat, and swelling. Medium veins in the range of 19 mm in diameter have a well developed intima, a media consisting of connective tissue and loosely organized smooth muscle, and an adventitia (usually the thickest layer) composed of collagen bundles, elastic fibers, and smooth muscle cells oriented along the longitudinal axis of the vessel. Venous valves are sheet-like outfoldings of endothelium and underlying connective tissue that form flaps to permit uni-di rectional flow of blood. Large veins, such as the external iliac, hepatic portal, and vena cavae, are the major conduits of return toward the heart. The intima is similar to that of medium veins ...»