kapillære

Kapillære are the smallest blood vessels in the body, forming a network that connects arterioles to venules. Their incredibly thin walls, typically only one cell thick, are essential for their primary function: facilitating the exchange of gases, nutrients, and waste products between the blood and the body's tissues. This process, known as capillary exchange, occurs through diffusion, filtration, and reabsorption.

The narrow diameter of capillaries, often just wide enough for a single red blood cell to pass through, slows blood flow and maximizes the surface area available for exchange. This also allows red blood cells to deform and pass through smoothly. Capillaries are distributed throughout virtually all tissues and organs, ensuring that every cell receives the necessary oxygen and nutrients and that waste products are efficiently removed.

The structure of capillaries is adapted to their role. Their walls are composed of a single layer of endothelial cells supported by a basement membrane. This thin, permeable barrier allows for easy passage of small molecules. Larger molecules and even some proteins can pass through through specific transport mechanisms or transient pores. The regulation of capillary blood flow is controlled by precapillary sphincters, which can constrict or dilate to direct blood to areas where it is most needed. This dynamic regulation ensures that tissues receive adequate blood supply based on their metabolic demands.