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RESEARCH PRODUCT

Functional Morphology of Human Arteries During Fetal and Postnatal Development

subject

description

The equilibrium between the distending force of the blood pressure and the arterial wall is determined essentially by a simple law of mechanics, the law of Laplace. According to this law, the total force or tension (T) in the vessel’s wall represents the product of the radius of the vessel (r) and the blood pressure (p), T = r.p. The law of Laplace may be used to estimate and compare the tension produced by blood pressure in vessels of different size and thereby determine the increase in functional load on arteries. Since tension increases not only with blood pressure but also with the radius of the vessel, the highest tension is presumably produced in the wall of the ascending aorta where tension amounts to about 200,000 dynes/cm, i.e., 200 g/cm. In the vena cava, which also has a wide lumen but is subject to a much lower blood pressure, the total wall tension is also high, about 20,000 dynes/cm, i.e., 20 g/cm, whereas in the capillary wall, tension is very low — 16 dynes/cm, i.e., 16 mg/cm. Since the radius is small, the thin wall of a capillary can withstand the distending force of capillary blood pressure (F 25 mm Hg.).