Why does veins contain valves
Although most veins take blood back to the heart, portal veins carry blood between capillary beds. For example, the hepatic portal vein takes blood from the capillary beds in the digestive tract and transports it to the capillary beds in the liver. The blood is then drained in the gastrointestinal tract and spleen, where it is taken up by the hepatic veins and blood is taken back into the heart. Since this is an important function in mammals, damage to the hepatic portal vein can be dangerous.
Blood clotting in the hepatic portal vein can cause portal hypertension, which results in a decrease of blood fluid to the liver. Veins are classified in a number of ways, including superficial vs. Privacy Policy. Skip to main content. Cardiovascular System: Blood Vessels. Search for:. The Venous System. Venules Venules are small blood vessels in the microcirculation that connect capillary beds to veins.
Learning Objectives Describe the venules of the venous system. What might explain this condition in terms of Is the vertebral artery a branch of the aortic arch? What conditions contribute to elevated blood levels of alkaline phosphatase?
Are lymphocytes produced in the bone marrow and then migrate to the thymus gland and lymph nodes What is heart disease? What is the primary cause of heart disease and what symptoms does it How does blood flow back to the heart from the lower extremities, since it is fighting against gravity?
In a heart transplant, if the vagus nerve is not re-transplanted, how is the heart rate kept in check? Pearce JM. The craniospinal venous system. Chummy S. Last's Anatomy.
Caggiati A. The venous valves of the lower limbs. Promoted articles advertising. Loading more images Close Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys. Varicose veins may ache or cause itching or a sensation of tiredness.
Doctors can detect varicose veins by examining the The veins in the legs are particularly at risk of blood clotting or swelling of the vein because when a person is standing, blood must flow upward from the leg veins, against gravity, to reach the heart. Merck and Co. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world.
The Manual was first published in as a service to the community. Learn more about our commitment to Global Medical Knowledge. This site complies with the HONcode standard for trustworthy health information: verify here. Common Health Topics. Problems With the Veins. Venous Disorders. Test your knowledge. An aortic dissection occurs when the inner layer lining of the aortic wall tears and separates from the middle layer of the wall.
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