Valves Handle High Pressures

Biological Strategy

Humans

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Liquids include water, as well as body fluids such as blood, gastric juices, nutrient-laden liquids, and more. To survive, many living systems must move such liquids within themselves or between locations. Because of their properties, liquids tend to disperse unless they are confined in some way. To address this, living systems have strategies to confine fluids for transport, and to overcome barriers such as gravity, friction, and other forces. Some of these same barriers also provide opportunities. Trees and giraffes face the same challenge: how to move fluids (water and blood, respectively) upward against gravity. But their strategies are quite different. The tree moves water using capillary action and evaporation, possibly due to water’s properties of polarity and adhesion. The giraffe’s tight skin provides pressure to assist in blood circulation. and keep blood from pooling in the legs.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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The aortic valve in vertebrate hearts allows the tissue to expand under high pressures by having elastic properties.

“THE human aortic valve consists of three cusps made of relatively inelastic, muscle-free material about 0.15 mm thick. It opens and shuts about once a second, and withstands a pressure difference of 100 mm of mercury when closed. It usually functions for 70 yr without failure, and works so efficiently that very little blood is regurgitated at each pulse. In order to support this large pressure difference, the cusps must close simultaneously in all operating conditions and should not touch the wall of the aorta, for considerable reversed flow would then be required to close the valve. This action suggests a fluid dynamic control mechanism which positions the cusps away from the wall of the aorta, so that the slightest reversed flow will close the valve.” (Bellhouse and Bellhouse 1968:86)

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References

“The human aortic valve consists of three cusps made of relatively inelastic, muscle-free material about 0.15 mm thick. It opens and shuts about once a second, and withstands a pressure difference of 100 mm of mercury when closed. It usually functions for 70 yr without failure, and works so efficiently that very little blood is regurgitated at each pulse. In order to support this large pressure difference, the cusps must close simultaneously in all operating conditions and should not touch the wall of the aorta, for considerable reversed flow would then be required to close the valve. This action suggests a fluid dynamic control mechanism which positions the cusps away from the wall of the aorta, so that the slightest reversed flow will close the valve.” (Bellhouse and Bellhouse 1968:86)

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Journal article

Mechanism of closure of the aortic valve.

Nature | Bellhouse, B. J.; Bellhouse, F. H.

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