Capillary

In blood circulatory system, the capillaries are the smallest blood vessels. They measure anywhere from 5 to 10 microns in diameter and are essential for microcirculation of nutrients and oxygen. They are located in the tissues of organs and assist in supplying them with oxygenated blood, glucose, and nutrients. Apart from this, cellular waste products, carbon dioxide and others are passed back through the capillaries. They are essential components of the circulatory system that work on the micro level between the arteries and the veins. As oxygenated blood is pumped from the heart through the arteries, they enter the arterioles. From the arterioles, they enter the capillaries and then to the cells. The cells are replenished with nutrients, and then the waste products of the cell are carried to the venules through the capillaries to the veins. Fluid exchange occurs in the capillaries through precapillary sphincters. When the sphincter opens, the fluid is allowed and when the sphincter is closed, the fluid is stopped. By this sphincter action and osmosis, fluids, nutrients, and gases are exchanged to supply the cells with glucose, and oxygen and to remove waste products. There are around 10 to 40 million capillaries in the body. They are abundant in the skin, eyes, spleen, liver, kidneys, thyroid, and other organs. They are generally arranged in networks called capillary beds consisting of true capillaries (those branching from arterioles). The capillary blood pressure is comparatively lesser than arterial and venous pressure due to its size and diameter. In people with diabetes, blood glucose measurements are made with blood drawn from the capillaries and from veins. The values of blood sugar levels often vary with both blood samples. People with diabetes also experience a damage to their capillaries. This is because of the microvascular damage diabetes causes. Diabetes is known to cause vessel wall stenosis, which can lead to capillary closure and a host of complications. In the eyes, it can cause diabetic retinopathy. In the kidneys, it can cause diabetic nephropathy. Capillaries get damaged in diabetes due to stiffening of the collagen and degeneration of the elastin.