Capillaries
Capillaries
Capillaries (/kəˈpɪləriːz/; from Latin capillaris, "of hair") are the smallest of a body's blood vessels and are part of the microcirculation. Their endothelial walls are just one cell thick. These microvessels, measuring 5-10 micrometres in diameter, connect arterioles and venules and enable the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste chemical substances between blood and the tissues.
Structure
Capillaries consist of a single layer of Endothelium cells over a thin base membrane, without any smooth muscle tissue. The capillary wall performs the function of a semi-permeable membrane that allows substances to pass through it depending on their size and charge.
Function
Capillaries are responsible for the actual exchange of oxygen and carbon dioxide between the blood and tissue cells. They also distribute nutrients to tissues and carry waste materials away from tissues.
Types of Capillaries
There are three types of capillaries: continuous, fenestrated, and sinusoidal.
- Continuous capillaries are the most common type and are found in most tissues of the body.
- Fenestrated capillaries have pores in the endothelial cells that are spanned by a diaphragm of radially oriented fibrils and allow small molecules and limited amounts of protein to diffuse.
- Sinusoidal capillaries are a special type of open-pore capillary, that have larger openings in the endothelium to allow red and white blood cells and various serum proteins to pass, a process that is aided by a discontinuous basal lamina.
See Also
External links
- Medical encyclopedia article on Capillaries
- Wikipedia's article - Capillaries
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