The venules are tiny blood vessels that return blood to the veins. Only 25 percent of a humans blood are contained in the venules.
The blood in venules of the systemic circulation is deoxygenated. The blood in pulmonary venules is oxygenated.
Capillaries converge to form venules. After the exchange of gases, nutrients, and waste products in the capillary beds, the deoxygenated blood collects into small veins known as venules. These venules then combine to form larger veins, ultimately returning blood to the heart.
Small postcapillary venules consist entirely of endothelium just like capillaries (the larger venules have smooth muscle and thin externa as well). Also both capillaries and venules have no elastic tissues. Postcapillary venules are extremely porous which makes them more like capillaries then veins, and fluid and WBC's move easily into the bloodstream through these walls.
venules
Venules
Venules
Veins
capillaries
Capillaries
The venules draining the small intestine combine to form the superior mesenteric vein.
Renal vein It is not renal vein. It is venules. renal vein is only at one point of the body, were talking capillaries; which are all over the body.
Arterioles are smaller vessels that carry blood away from the heart, while venules are smaller vessels that carry blood back to the heart. By observing the direction of blood flow and the presence of valves (which venules have), one can distinguish between arterioles and venules in the frog's foot vasculature.