Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 23

Since the plasma membrane is a fluid structure consisting predominantly of phospholipid, molecules that are fat-soluble are able to dissolve in the phospholipid bilayer and pass rapidly across by a process called simple diffusion.

Simple diffusion can be defined as:

The passive movement of molecules from a region of high concentration to a region of low concentration until an even distribution of molecules (equilibrium) is achieved.

Gases such as oxygen and carbon dioxide and lipid-based hormones such as steroids including testosterone and oestrogen are highly soluble in the fluid phospholipid bilayer and pass readily into and out of cells via simple diffusion. Simple diffusion also occurs rapidly in the lungs with oxygen inspired at high concentration from the atmosphere before diffusing rapidly across the alveolar air sacs into the blood. Conversely, carbon dioxide is at high concentration in the blood and passes across into the alveoli by simple diffusion before being eliminated during expiration. Concepts such as diffusion are often very abstract in nature, so to help consolidate your understanding of this process, attempt Activity 1.2.