Directory 1 Note: This is the redirection portal, and * * * enjoys the content of capillaries. For the convenience of reading, the capillaries in the following paragraphs have been automatically replaced by capillaries. You can click here to restore the original appearance, or you can use the remarks to display 1 to mark the capillary. The finest blood vessels are distributed among various tissues and cells. Between arterioles and venules. The average diameter is 7 ~ 9 microns, and the number is very large, showing a network distribution.

The tube wall consists of a layer of endothelial cells and a thin basement membrane, with a thickness of about 0.5 micron. There is a thin layer of connective tissue outside the basement membrane, including fibroblasts, macrophages and pericytes. The thinnest microvessel is surrounded by one endothelial cell, and the thicker microvessel is surrounded by 2 ~ 3 endothelial cells. Microvessels distributed in muscle tissue, nerve tissue and connective tissue are connected by gaps between endothelial cells (gap width is 150 angstrom), which is called continuous microvessels. Microvessels are distributed in endocrine glands, kidneys and so on. In addition to gap junction, the cell itself has many pores (pore size 800 ~ 1000 angstrom), which are called porous microvessels. Microvessels distributed in liver, spleen, bone marrow and some endocrine glands all have enlarged lumens, which are called blood sinuses. Microvessels with thin wall, high permeability, small diameter (8 ~ 10 micron), large number and slow blood flow are places where blood and tissue fluid exchange substances, also known as exchange blood vessels. Blood sinus is formed by the enlargement of microvascular lumen. The general structure of the sinus wall is the same as that of the microvascular wall, which consists of a single layer of endothelial cells, and there are windows on the endothelial cell membrane. The sinus wall structure of different organs is different. There are wide cracks between endothelial cells of splenic sinus; The endothelial cells in hepatic sinuses are discontinuous and the intercellular space is wide (0. 1 ~ 0.5 μ m). The basement membrane of hepatic and splenic sinuses is incomplete or without basement membrane, and its permeability is greater than that of microvessels, so larger protein and blood cells can pass through. There are kupffer cells in the wall of hepatic sinus, and macrophages inside and outside splenic sinus. These two types of cells have phagocytic ability, which can phagocytize and remove foreign bodies, bacteria and other harmful substances in the blood, and are an important part of mononuclear phagocytic cell system. The blood sinuses of some endocrine glands have a continuous basement membrane.