Kapillærvæggenes

Kapillærvæggene, or capillary walls, are the thin walls that form the boundaries of capillaries, the smallest and most numerous blood vessels in the body. They play a crucial role in the exchange of substances between the bloodstream and the surrounding tissues. The structure of capillary walls varies depending on the type of capillary, but they generally consist of a single layer of endothelial cells, a basal lamina, and an underlying layer of pericytes.

Endothelial cells are flat, continuous cells that line the inner surface of capillaries. They are tightly joined by junctional complexes, which prevent the leakage of blood components into the surrounding tissues. The basal lamina is a thin, extracellular matrix that provides structural support and acts as a barrier to the passage of large molecules. Pericytes are contractile cells that wrap around the capillaries and help regulate blood flow and vascular tone.

The permeability of capillary walls is regulated by various factors, including the diameter of the capillaries, the tightness of the endothelial junctions, and the presence of regulatory molecules. In continuous capillaries, which are found in most tissues, the endothelial cells are tightly joined, and the basal lamina is thick, resulting in low permeability. In fenestrated capillaries, which are found in the kidneys and endocrine glands, the endothelial cells have small pores or fenestrae, allowing for the exchange of small molecules and ions. In sinusoidal capillaries, which are found in the liver and spleen, the endothelial cells are discontinuous, and the basal lamina is thin, resulting in high permeability.

Kapillærvæggene are essential for maintaining the homeostasis of the body by facilitating the exchange of nutrients, oxygen, and waste products between the bloodstream and the surrounding tissues. They also play a role in immune defense by allowing the passage of immune cells and molecules into the tissues.