What Are Peritubular Capillaries?

Microvessels are tiny blood vessels of the cardiovascular system that can be seen under a microscope. Microvessels refer to the small blood vessels that connect the small arteries and venules. They are distributed in various tissues and organs and branched into a network, so they are also called terminal vascular beds. In the order of blood vessel branching, microvessels mainly include arterioles, capillaries, and venules; some also have two short circuits that directly connect the arteries and venules: straight access and arteriovenous anastomosis.

Microvessels are tiny blood vessels of the cardiovascular system that can be seen under a microscope. Microvessels refer to the small blood vessels that connect the small arteries and venules. They are distributed in various tissues and organs and branched into a network, so they are also called terminal vascular beds. In the order of blood vessel branching, microvessels mainly include arterioles, capillaries, and venules; some also have two short circuits that directly connect the arteries and venules: straight access and arteriovenous anastomosis.

Western Medicine Name

Capillaries

Chinese Medicine Name

Capillaries

English name

capillary

Other name

Blood vessel

Affiliated Department

Internal Medicine-Hematology

Contagious

Non-contagious

Capillary composition

In tissues and organs, one or several arterioles and veins and the capillaries between them constitute the basic unit of microcirculation. Because the structures and functions of various tissues and organs are different, the distribution and composition of microvessels in each tissue have their own characteristics.

arterioles capillaries venules are common patterns;

arterioles capillaries venules, but arteriovenous anastomosis between arteries and venules;

Capillary Vein Capillary, the vein connecting the two groups of capillaries is called portal vein, this type is less, and is found in the liver and lower thalamus-pituitary gland;

Input arterioles capillaries output arterioles capillaries, found in kidneys and islets.

Capillary structure

Arterioles

Also called arterioles, the intima is composed of the endothelium, substrate and subendothelium. Endothelial cells are flat, and the connections between cells are similar to arteries. There are protrusions at the base that pass through the inner elastic membrane to form muscle-endothelial connections with nearby smooth muscle cells, which may pass certain biologically active substances in the blood to muscle cells. The arteries of the central nervous system are mostly without muscle-endothelial connections, and the substrate is thin or inconspicuous. The subendothelial layer is thin and formed from loose connective tissue, with a small amount of collagen fibers and elastic fibers. The inner elastic membrane is thin with window holes. The median membrane is smooth muscles arranged in two or three layers. There are elastic fibers between muscle cells, and an outer elastic membrane separates the median and adventitia. The mediastinum is rich in sympathetic nerves that govern the contraction of smooth muscle. The outer membrane is thin and consists of loose connective tissue, with or without myelinated nerve fibers and nerve endings, containing macrophages, mast cells, plasma cells, and fibroblasts.

Intermediate arterioles

They are collateral or terminal segments of the terminal arterioles, which are tapered, and whose walls are composed of an endothelium and a layer of discontinuous smooth muscle cells. Some have intimal pads similar to arteries. The smooth muscle cells of the intermediate arterioles have protrusions that extend along the longitudinal axis of the vessel. This blood vessel is the main gate that regulates the blood flow of microvessels. The vasomotor contraction cycle is about 2 to 8 seconds. Sympathetic nerve excitation causes the blood vessels to continue to contract, increasing blood flow resistance. Vasoconstriction can cause gradient changes in water and electrolytes in capillary blood flow.

Real capillaries

Capillaries are the most minute blood vessels distributed in the tissues and cells of various organs, and are distributed in a network, with an average diameter of 7-9 m. Because the tube wall has only a layer of flat endothelial cells, oxygen and nutrients in the blood penetrate into the tissues through this. Metabolites between cells and tissues enter the bloodstream. Capillary endothelial cells have window holes, some contain swallowing vesicles, and there are large gaps or gaps between adjacent endothelial cells. These are the morphological foundations for capillary exchange of substances.

Microvenous

There is a gradual change from true capillaries to venules, which are roughly divided into three sections: posterior capillary venules, collecting venules and muscular venules:

Microcapillary veins: 8-30 m in diameter and 50-70 m in length, formed by 2 to 4 capillaries. Their wall structure is similar to that of capillaries. There is a continuous layer of endothelium, and some endothelial cells have window holes and diaphragms. Cells are loosely connected to each other, and there is often a gap of 6 nm between cells, which can pass molecules with a size of 5 to 5.5 nm. The endothelial cells of the capillary veins behind the capillaries in the lymphoid organs are cuboids and are the main entry and exit sites of lymphocytes;

Collective venules, also called pericytic venules, have a diameter of 30-50 m. Their wall structure is characterized by a more complete layer of peripheral cells around the endothelium, and occasionally smooth muscle cells;

Muscle venules: 50 100m in diameter, there are 1 2 layers of smooth muscle around the endothelium, and the outer membrane is very thin. The venules, especially the venules behind the capillaries, play an important role in material exchange. They are permeable to macromolecular substances. Compared with capillaries, venules are more susceptible to temperature, inflammation and allergic reactions. They are sensitive to histamine, serotonin, bradykinin, and prostaglandins, which can easily cause cell connections to loosen or crack, and cause Leakage of blood cells.

Capillary function

The functions of microcirculation of various tissues and organs are different, some mainly provide nutrition and excrete metabolites; some mainly regulate or maintain a constant local environment, such as regulating body temperature, gas exchange, excretion, and hormone delivery. Microvascular function is regulated by nerve and humoral factors, some are rich in vascular motor nerves, and some are sensitive to substances released from nearby cells.