Question

What is the smallest vein in Human body?

Answer 1

Hint: Human blood flows inside tubes called blood vessels. Blood vessels are of three types- Arteries, Veins, and Capillaries. The blood vessels help to transport oxygen, nutrients and hormones to different parts of bodies and removes waste material produced during metabolic reactions from cells to the outside.

Complete answer:
Veins are the collecting blood vessels that carry blood from various parts of the body towards the heart. Valves are present inside these veins to prevent backflow of blood. They carry deoxygenated blood except pulmonary veins that bring oxygenated blood from the lungs to the heart. The walls of veins are comparatively thinner and less elastic than arteries. They have a wide lumen. Blood flows smoothly and slowly inside veins hence there is little pressure.
The smallest veins in the body are known as venules. Blood reaches the venules, from the arteries via the arterioles and capillaries. The venules join into larger veins which eventually carry the blood to the largest veins in the body called vena cava. Blood is then transported from the superior vena cava and inferior vena cava to the right atrium of the heart. There are three types of veins- pulmonary veins, deep veins, and superficial veins.
Pulmonary veins- they carry oxygenated blood from the lungs to the heart.
Deep veins- They are present deep inside our body near the muscle tissue.
Superficial veins- They are present near the surface of our skin and are visible. They appear blue or greenish in colour.

Note:
Veins are present superficially in our body. The blood vessels that are visible to our eyes are all veins. Veins are collapsible. They are full of blood even after death.
Thebesian vein is the smallest cardiac vein. They are valveless veins, that is they don’t have valves present in them. They are present in the walls of all the four chambers.