Question

Which of the following is an example of a portal vein?

Answer 1

Veins carry carbon dioxide in the blood except for a pulmonary vein that carries oxygenated blood from lungs to heart. So pulmonary arteries and pulmonary veins do not carry carbon dioxide. veins emerge from each lung hilum, receiving blood from three or four bronchial veins a piece and draining into the left atrium.

Complete answer:
The portal vein or hepatic vein is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents.
Examples of portal veins are venous blood to the liver. It is formed by the confluence of superior mesenteric, splenic veins, inferior mesenteric, left, right gastric veins and the pancreatic vein.
The portal vein and hepatic arteries form the liver’s dual blood supply. Approx. $75\%$ of hepatic blood flow is derived from the portal vein, while the remains are from hepatic arteries. Unlike other veins, the portal vein does not drain into the heart. Rather it is a venous system which ports blood into capillaries.
Increasing blood pressure in the portal vein called portal hypertension. It is a major complication of liver disease, most commonly cirrhosis. Clinical signs of portal hypertension include those of chronic liver disease like- ascites, esophageal varices, spider nevi, palmar erythema. Collectively, these veins are called the hepatic portal venous system and are an important source of complications in patients with chronic liver disease.
Rarely, children may be born with an absent or underdeveloped portal vein. This condition is known as congenital agenesis of the portal vein. Which also can be related to abnormalities of liver or cardiovascular system. Symptoms may include direct flow of blood from intestine and spleen into systemic veins.

Notes:
Prognosis depends on the nature of the liver and cardiac disease. As well as the location of the shunts. These patients can sometimes manage with medications or surgical procedures. In severe cases liver transplantation may be necessary. So, as we discussed about what portal vein is, its function and importance examples of the vein.