kapilari

Kapilari, scientifically known as capillaries in English, are the smallest blood vessels in the circulatory system, forming the microcirculation between arterioles and venules. Their walls consist of a single layer of endothelial cells supported by a thin basement membrane, and they are often enmeshed with pericytes. The narrow diameter, about 5 to 10 micrometers, and thin walls facilitate the exchange of gases, nutrients, and waste between blood and surrounding tissues.

Capillaries are classified into three main structural types: continuous, fenestrated, and discontinuous (sinusoidal). Continuous capillaries have uninterrupted endothelium and are common in muscle, skin, and the brain, though brain capillaries feature tight junctions contributing to the blood–brain barrier. Fenestrated capillaries possess pores that enhance exchange and are found in the kidneys, small intestine, and endocrine glands. Discontinuous capillaries have larger gaps and incomplete basement membranes, enabling rapid transfer of larger molecules and even cells in organs such as the liver, spleen, and bone marrow.

Exchange across capillaries occurs mainly by diffusion of oxygen, carbon dioxide, glucose, amino acids, and other solutes. Fluid movement is governed by Starling forces, balancing filtration and reabsorption, with transcytosis contributing to selective transport in some tissues. Local vascular regulation, including precapillary sphincters and capillary recruitment, links blood flow to tissue metabolic demand.

Capillaries play a key role in development, tissue repair, and immune responses. Abnormal capillary function or density is associated with various diseases, including diabetes-induced microangiopathy and chronic inflammation.