What are venules?

Venules are a type of blood vessel found within the circulatory system. All blood vessels carry blood from the heart to the body or from the body back to the heart. Arteries and arterioles carry blood from the heart to the body, while veins and venules carry blood back to the heart.

The circulatory system is made up of arteries and arterioles, veins, venules, and capillaries. As the blood vessels move away from the heart, they branch out to form smaller vessels. Capillaries are the smallest blood vessels. They are only one cell thick and their walls are also very thin. This allows oxygen to move out of the blood to surrounding cells and carbon dioxide to move out of the cells into the blood.

Arteries and veins are the largest blood vessels and are closest to the heart. They branch to form smaller arterioles and venules. Capillaries act as the link between arterioles and venules, making the circulatory system a complete system for blood flow.

Venules join capillaries to veins when blood is transported back to the heart and lungs. A vein is much larger than a venule and can carry a much larger volume of blood. Many venules will join with a single vein to carry blood.

Most of the blood carried by the venules is deoxygenated blood. This means that the blood passed through various tissues and organs within the body and oxygen passed from the blood to the cells of the body. The blood must now travel back to the lungs so it can pick up more oxygen to carry back to the body.

When blood leaves the heart, it is pumped around the body by the contractions of the heart, but the same is not true for blood returning to the heart. Blood flow within veins and venules is much slower than in arteries and arterioles. The blood is pumped by contractions in the muscles of the extremities, for example, the legs.

Most of the blood flows against gravity when it travels back to the heart and lungs. Semilunar valves are present within each venule and vein to prevent blood from flowing into the vein or venule. These valves are necessary because blood is not pumped as forcefully and to counteract the effects of gravity on slower moving blood.

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