Quick Facts
A continuous capillary is one of the two major types of capillaries, found in muscle, skin, lung, central nervous system, and other tissues, and characterized by an uninterrupted endothelium, a continuous basal lamina, fine filaments, and numerous pinocytotic vesicles (Dorland, 2011).
Structure and/or Key Features
Capillaries are the smallest blood vessels, often smaller than the diameter of an erythrocyte (red blood cell). They are very thin-walled and made of endothelial cells that form a tube and their supporting basement membrane. Based on their morphology they are classified as being continuous (non-fenestrated), fenestrated, or discontinuous capillaries.
Continuous capillaries are found in connective tissues, muscle tissue, skin, lungs, and in the central nervous system. Each endothelial cell is joined by tight (occluding) junctions.
Fenestrated capillaries are common in endocrine glands, the kidney, pancreas and the digestive tract. Endothelial cells exhibit very small openings, called fenestrations, through the capillary wall about 70–80 nm in diameter.
Capillaries in the liver, spleen, and bone marrow are typically discontinuous capillaries. The endothelial cells have wide gaps in their cytoplasm and are supported by a discontinuous basement membrane (Ross and Pawlina, 2006).
Anatomical Relations
Capillaries are extensive blood vessel networks within tissues at the end of the arterial tree. They link up with venules so blood returns back to the right side of the heart to be then redirected and re-oxygenated in the lungs.
Function
Capillaries are closely associated with cells and tissues, and so are suited for the exchange of waste products and metabolites, gases, nutrients, etc. between the blood circulation and the extracellular environment of a tissue. Capillaries also deliver chemical messengers from sites of secretions to target organs.
Tight junctions of continuous capillaries restrict exchange with the extracellular environment occurring between endothelial cells.
Fenestrated capillaries facilitate fluid and metabolite absorption.
Discontinuous capillaries permit passage of large proteins e.g., blood plasma proteins across the capillary wall (Ross and Pawlina, 2006).
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Ross, M. H. and Pawlina, W. (2006) Histology: A text and atlas. Lippincott Williams & Wilkins.
