English for doctors. Surface tension forces (most important)

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English for doctors. Surface tension forces (most important)

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33. Surface tension forces

In a liquid, the proximity of adjacent molecules results in large, intermolecular, attractive (Van der Waals) forces that serve to stabilize the liquid. The liquid-air surface produces inequality of forces that are strong on the liquid side and weak on the gas side because of the greater distance between molecules in the gas phase. Surface tension causes the surface to maintain as small an area as possible. In alveoli, the result is a spherically-curved, liquid lining layer that tends to be pulled inward towards the center of the curvature of the alveolus. The spherical surface of the alveolar liquid lining behaves in a manner similar to a soap bubble. The inner and outer surface of a bubble exert an inward force that creates a greater pressure inside than outside the bubble. Interconnected alveoli of different sizes could lead to collapse of smaller alveoli (atelectasis) into larger alveoli, because of surface tension, the pressure inside the small alveolus (smaller radius of curvature) is greater than that of the larger alveolus. Without surfactant, gas would therefore move from smaller to larger alveoli, eventually producing or giant alveolus.

Pulmonary surfactant: Pulmonary surfactant is aphospho-lipid (comprised primarily of dipalmitoyl phosphatidylcholi-ne) synthesized by type II alveolar epithelial cells. Surfactant reduces surface tension, thereby preventing the collapse of small alveoli. Surfactant increases the compliance of the lung and reduces the work of breathing.

Surfactant keeps the alveoli dry because alveolar collapse tends to draw fluid into the alveolar space. Surfactant can be produced in the fetus as early as gestational week 24, but is synthesized most abundantly by the 35th week of gestation. Neonatal respiratory distress syn drome can occur with premature infants, and results in areas of atelectasis, filling of alveoli with transudate, reduced lung compliance, and V/Q mismatch leading to hypoxia and CO ₂ retention

new words

surface tension forces - surface tension forces

liquid - liquid

proximity - proximity

adjacent - adjacent

intermolecular - intermolecular

to stabilize - stabilize

surface - the surface

distance - the distance

phase - phase

tension - tension

spherically-curved - spherically-curved

lining - alignment

inward - inside

towards - to

curvature - curvature

spherical - spherical

soap bubble - soap bubble

inner - internal

to exert - show

interconnected - connected

Author: Elena Belikova

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