Blood circulates in our bodies through an amazing network of blood vessels called arteries, veins and capillaries. Capillaries are the smallest blood vessels, being thin and fragile with a diameter of only ten micrometres. They are made of endothelium, a single layer of cells that only allow red blood cells to flow through them in a single file due to their narrow wall structures.
Capillaries form a bed of tiny vessels but with a large surface area within the tissues of the body. They receive oxygenated blood from the arteries through precapillary sphincters that open to allow the blood to flow through. Gases like oxygen and other nutrients like proteins and amino acids are released from them by diffusion into the surrounding tissues of the body. Carbon dioxide and other waste substances are passed on to the veins as waste blood to go back to the heart. According to the type and degree of diffusion required the capillary walls can differ in their thickness. Continuous capillaries allow diffusion of smaller molecules, fenestrated capillaries allow larger molecules and sinusoidal capillaries have larger openings that allow red blood cells and proteins to diffuse into the surrounding tissues.
The organs in the body get their supply of oxygen from the network of capillaries and lymph fluid flows through capillaries ensuring the body gets the maximum amount of oxygen and essential nutrients. They also enable the body to dispose off the waste products being produced through the blood stream. While some parts of the body like the liver and kidneys require a larger capillary network due to their metabolic rates other areas like the epidermis and parts of the eye like the lens and cornea do not require a large capillary network.
The capillaries are also responsible for other body functions like blood clotting and controlling blood pressure. Their healthy function ensures good blood circulation so that the body gets adequate supplies of oxygen and other necessary nutrients for its optimum functioning. Ensuring a good diet and a healthy lifestyle will help strengthen capillaries for good circulation. It is also advisable to avoid excessive smoking and drinking to keep damage to body cells to a minimum.
Another function of the capillaries is to regulate the temperature of the body. They do this by releasing heat generated in the blood into the surrounding tissues to avoid the blood being overheated with the result that the skin appears red. Sometimes hormonal disorders, genetic reasons, temperature extremes or hot spicy food can cause damage to the capillaries resulting in spider veins on the face and nose.