There are 9 ~ 10 pairs of venous valves in the lumen of great saphenous vein. Usually, the two valves are opposite and bag-shaped, which can ensure blood to return to the heart. In addition, the great saphenous vein and the small saphenous vein communicate with the deep vein through veins. The valve passing through the vein faces the deep vein, so that blood can flow from the superficial vein into the deep vein. When the deep venous return is blocked, the venous valve is not completely closed, and the deep venous blood flows back to the superficial vein, which may lead to varicose veins of the lower limbs.
Extended data
Grading:
Venules:
Capillaries gradually become veins, and only a thin layer of connective tissue is initially added around the endothelium. When the diameter reaches 50μm, sparse smooth muscle appears between endothelium and connective tissue. When the diameter is large, the smooth muscle becomes a complete layer, and those with a diameter less than 500μm belong to venules. Veins with a diameter of 0.2 ~ 1 mm are called venules. The intima of venules has only endothelium, the medial membrane has 2 ~ 4 layers of smooth muscle, a small amount of elastic fibers and collagen fibers, and the adventitia is thin and composed of connective tissue.
Intermediate vein:
The diameter of blood vessels is 1 ~ 10 mm, and the wall thickness is about110. In addition to the trunk of vein, anatomically named visceral vein and distal limb vein belong to this category. The intima is thin, the endothelial cells are polygonal, and the endothelium is thin or inconspicuous, containing a small amount of collagen fibers, elastic fibers and fibroblasts. Most of them have no internal elastic membrane, but the blood vessels of lower limbs have thin internal elastic membrane.
The tunica media is thin and dense annular smooth muscle bundles with a little connective tissue between them. The external elastic membrane is thin or non-existent. The adventitia is quite thick, made by connectivetissue. Some blood vessels have more longitudinal smooth muscle bundles, including nutrient blood vessels, lymphatic vessels and nerves.
Great vein:
Their diameters are all more than 9 ~ 10 mm, including external jugular vein, innominate vein, azygos vein, pulmonary vein, external iliac vein, renal vein, adrenal vein, superior mesenteric vein, splenic vein, portal vein and vena cava. The wall of great vein is thin, which is about 1/20 in diameter. The structure of intima is basically the same as that of middle vein. The subcutaneous tissue contains collagen fibers, elastic fibers and longitudinal smooth muscle bundles.
The internal elastic membrane has a large window or rupture. The medium is thin and consists of several layers of smooth muscle, or there is no medium. The outer elastic membrane is not obvious or does not exist. The outer membrane is the thickest, several times thicker than the middle membrane, composed of connective tissue, containing longitudinal elastic fibers and collagen fiber bundles, and often has more longitudinal smooth muscle. There are more nutrient blood vessels and lymphatic vessels than arteries, which can penetrate deep into the intima and are also rich in nerves.
Atypical vein:
The intima of cephalic vein, basilic vein, mesenteric vein, iliac vein, femoral vein, popliteal vein, saphenous vein, uterine vein and dorsal penis vein contains longitudinal or annular smooth muscle. The middle smooth muscle of saphenous vein, femoral vein and popliteal vein is mostly vertical; The media of adrenal vein is almost longitudinal smooth muscle. The adventitia of renal vein, portal vein, splenic vein and phrenic vein is mainly composed of longitudinal smooth muscle.
A long section of superior vena cava and inferior vena cava has no inner side wall, and the outer membrane is thick and rich in longitudinal smooth muscle. The pulmonary vein media is thick, with longitudinal smooth muscle and less elastic tissue. The medial membrane of umbilical vein has medial longitudinal smooth muscle and outer ring smooth muscle. Some veins lack smooth muscle, so there is no medium, such as penile cavernous vein, placental mother vein, splenic trabecular vein, skin and nail bed vein, dural sinus, meninges and cerebral veins, retinal veins and bone veins.
The tunica media of great veins (such as vena cava, jugular vein, innominate vein and subclavian vein) contain collagen fibers and more elastic tissues, most of which are incomplete membranes and alternate with smooth muscle. The venous plexus of spermatic tendril is thick, rich in connective tissue and smooth muscle, less in elastic tissue, and the boundary between media and adventitia is not obvious.
A segment of vena cava and pulmonary vein near the heart, with annular myocardial fibers in the adventitia and a small amount of longitudinal myocardial fibers where these blood vessels lead to the heart.
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