What are veins? Detailed explanation of the classification of human veins

Blood vessels are channels for blood circulation. Without these blood vessels, blood from the heart may not be transported smoothly, and the human body will be in danger of death. Blood vessels are divided into two major categories, namely veins and arteries. Relatively speaking, people know relatively little about veins.

What are veins?

Blood that flows back to the heart through the capillaries or that spurts from the heart to the lungs is called venous blood. The walls of veins are thin, less elastic, have venous valves, and have slow blood flow, making varicose veins more likely to develop (especially in the lower limbs). Because blood exchanges nutrients with the body's tissues in the capillaries, venous blood is dark red.

Common veins

Upper limb veins

The deep veins of the upper limbs all run along with the arteries of the same name. The superficial veins of the upper limbs are: The craniocephalus vein starts from the radial side of the dorsal venous network of the hand, ascends along the forearm and the outer side of the arm, and merges into the axillary vein. The primary vein starts from the ulnar side of the dorsal venous network of the hand, ascends along the ulnar side of the forearm. It merges with the brachial vein at the midpoint of the inner side of the arm, or accompanies the brachial vein upward to be injected into the axillary vein. The median cubital vein connects between the craniocephalus vein and the primary vein in front of the elbow.

Chest veins

The right intercostal vein, bronchial vein and esophageal vein merge into the azygos vein, while the left intercostal vein first merges into the semi-azygos vein or accessory semi-azygos vein, and then into the azygos vein. The azygos vein ascends along the right front of the thoracic vertebral body, arches over the right lung root and merges into the superior vena cava.

Veins of the lower extremities

The deep veins of the lower limbs run along with the arteries of the same name, continuing from the femoral vein to the external iliac vein. The superficial veins of the lower limbs are: the large hidden vein, which originates from the medial end of the dorsal venous arch of the foot, ascends along the medial side of the lower limb along the front of the medial malleolus, and merges into the femoral vein at the upper end of the anterior thigh. The small hidden vein originates from the lateral end of the dorsal venous arch of the foot, passes behind the lateral malleolus, ascends along the back of the calf, and injects into the popliteal vein at the popliteal fossa.

Pelvic vein

There are parietal branches and visceral branches. Parietal branches run along with the arteries of the same name. Visceral branches originate from the venous plexuses around the pelvic organs (such as the vesical plexus, uterine vaginal plexus, and rectal plexus). Both parietal branches and visceral branches flow into the internal iliac vein. The external iliac vein and the internal iliac vein merge into the common iliac vein in front of the sacroiliac joint.

Abdominal veins

The veins in the abdomen are divided into parietal branches and visceral branches. Parietal branches run along with the arteries of the same name and are emptied into the inferior vena cava. Visceral branches, like arteries, can also be divided into paired visceral branches and unpaired visceral branches. Paired visceral branches have the same name as arteries, and most of them are directly emptied into the inferior vena cava; unpaired visceral branches include the superior mesenteric vein, inferior mesenteric vein, and splenic vein that originate from the intestines, spleen, pancreas, and stomach, etc. They converge to form a main venous trunk called the portal vein. The portal vein enters the liver through the hepatic portal vein, branches repeatedly in the liver, and finally merges with the branches of the hepatic artery into the hepatic sinusoidal space, which merges into the intrahepatic small veins, and finally forms three hepatic veins that are injected into the inferior vena cava. The portal vein is a special part of the inferior vena cava system. It transports a large amount of substances absorbed from the stomach and intestines to the liver, where they are synthesized, detoxified, and stored by liver cells.