Capillary permeability refers to the ability of capillaries, the smallest blood vessels in the body, to allow the passage of fluids, molecules, and other substances through their walls and into surrounding tissues. It is a physiological property that plays a crucial role in various bodily processes such as nutrient and waste exchange, immune response, and inflammation.
The capillary walls are composed of a single layer of endothelial cells, which are selectively permeable. This means that they can regulate the movement of substances based on their size, charge, and solubility. Small molecules, such as oxygen, carbon dioxide, glucose, and water, can easily diffuse through the endothelial cells due to their small size and lipid solubility. Larger molecules, such as proteins and blood cells, however, require special mechanisms to cross the capillary walls.
The permeability of capillaries can be influenced by numerous physiological factors, including local chemical signals, blood flow, and inflammation. Certain substances, called mediators, can increase capillary permeability by causing the endothelial cells to contract and form gaps or fenestrations. This phenomenon, known as increased vascular permeability, allows fluid and cells to escape from the capillaries, leading to tissue swelling and inflammation.
Clinically, capillary permeability is assessed using various techniques such as the measurement of hemoglobin leakage or the extravasation of fluorescent dyes. Abnormal capillary permeability can occur in certain diseases, such as sepsis, allergies, and vascular disorders, and can lead to edema (fluid accumulation in tissues) or impaired immune responses.
In summary, capillary permeability refers to the property of capillaries that allows the passage of fluids and molecules through their walls into surrounding tissues. It is a crucial aspect of many physiological
