What are veins? What are the causes of thin veins?

There are thousands of blood vessels of various sizes in the human body, and blood vessels are mainly divided into two categories, arteries and veins. Relatively speaking, veins are not as powerful as arteries, but they should not be underestimated. Some people in life find that their veins have become thinner. What is the reason?

Why do blood vessels become narrower?

In a physiological state, blood vessels can contract and retract to adjust the required blood pressure and blood supply, and this contraction is necessary. If certain blood vessels, such as the coronary arteries of the heart, are stenotic (thrombus), and vasospasm occurs, it can lead to critical conditions such as myocardial ischemia and even sudden death.

What do veins mainly refer to?

Veins are the tubes in the cardiovascular system that conduct and transport blood back to the heart.

The walls of veins are thin, with fewer smooth muscles and elastic fibers, lacking contraction and elasticity, and a flatter cross-section. Veins are blood vessels that carry blood back to the heart, starting from the capillaries and ending at the atria. The blood in the systemic veins contains more carbon dioxide and is dark red. The blood in the pulmonary veins contains more oxygen and is bright red. Small veins start from the capillaries and gradually merge into the middle veins and large veins during the process of returning to the heart, and finally flow into the atria. There are venous valves on the walls of the veins, especially in the veins of the lower limbs, where there are more and more developed ones. They can prevent blood from flowing back and allow blood to flow toward the heart. However, the large veins in the abdominal cavity, such as the portal vein, the superior and inferior caval veins, do not have venous valves, and the blood return to the veins may be affected by the intra-abdominal pressure.

The veins of the macrocirculation can be divided into the superior caval vein, the inferior caval vein and the cardiac vein. The superior caval vein: The superior caval vein is formed by the left and right brachiocephalic veins joining behind the first costochondral joint on the right side, descending vertically and entering the right atrium.