Quick Facts
A capillary network is any of the minute vessels that connect the arterioles and venules, forming a network in nearly all parts of the body. Their walls act as semipermeable membranes for the interchange of various substances, including fluids, between the blood and tissue fluid. The two principal types are continuous and fenestrated capillaries (Dorland, 2011).
Structure
Capillary vessels form a vascular network known as capillary beds. These capillary networks supply all the body's organs and tissues in the form of an interlacing web of capillaries. Capillaries have only one layer, the tunica intima, consisting of endothelial cells and their basal lamina.
The tunica intima is made up of a single layer of endothelial cells, a very thin basal lamina, and scattered pericytes. The basal lamina provides support to the endothelial cells, while the pericytes provide contractility.
Anatomical Relations
Extensive branching of capillary beds enables capillaries to be in contact with every cell. The rate of blood flow within a capillary bed is slow due to its highly branched nature. This slow blood flow, along with their very thin walls means that capillary beds are the ideal site for exchange of molecules.
Function
The thin walls of capillaries allow for the exchange of gases, nutrients, hormones, and waste products between blood and tissue cells:
List of Clinical Correlates
- Age-related macular degeneration
- Coronary heart disease
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
