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Etymology: L, capillaris, hairlike, permeare, to pass through
a condition of the capillary wall structure that allows blood elements and waste products to pass through the capillary wall to tissue spaces.
The condition of the capillary wall that enables substances in the blood to pass into tissue spaces or into cells, or vice versa.
See also: permeability
1. pertaining to or resembling a hair.
2. one of the minute vessels connecting arterioles and venules, the walls of which act as a membrane for interchange of various substances between the blood and tissue fluid. (See circulatory system.) The walls consist of thin endothelial cells through which dissolved substances and fluids can pass. At the arterial end, the blood pressure within the capillary is generally higher than the pressure in the surrounding tissues, and the blood fluid and some dissolved solid substances pass outward through the capillary wall. At the venous end of the capillary, the pressure within the tissues is generally higher, and waste material and fluids from the tissues pass into the capillary, to be carried away for disposal. See starling's hypothesis.
a capillary with no pores or other interruptions in the endothelial walls, e.g. in muscle, lung, nervous system.
capillaries with pores are scattered throughout the endothelial walls, e.g. in endocrine glands, intestines, kidneys.
see capillary fragility.
the smallest lymphatic vessel. Consists of an endothelial tube embedded in connective tissue.
see fenestrated capillary (above).
ability of large molecules to pass out of the capillary lumen into surrounding tissue spaces; inflammation, allergy, poisoning, burns cause increased permeability resulting in plasma leakage and edema in surrounding tissues.
capillary refill time (CRT)
the time required for mucosa (oral in horse or dog, vaginal in cow, sheep) which has been blanched by finger pressure to return to a normal pink color. Failure to return promptly is an indication of peripheral circulatory failure, due for example to dehydration or hypovolemic shock.
part of the vasculature of avian skin. Occur together with standard capillaries but they are larger in diameter and may have some smooth muscle cells associated with the endothelial cells.
large and irregularly shaped; occur in endocrine glands, aortic and carotid bodies.