Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 25

Since many of the molecules required by cells are water soluble and not particularly soluble in lipid, they cannot pass across the plasma membrane by simple diffusion. Facilitated diffusion makes use of channel proteins which function as physical passageways to carry molecules across the plasma membrane.

Facilitated diffusion can be defined as:

The passive movement of molecules across the plasma membrane from a region of high concentration to a region of low concentration aided (facilitated) by membrane channel proteins.

Facilitated diffusion is particularly important for getting water-soluble molecules such as sugars, e.g. glucose, into cells. Indeed, as we will see in Chapter 5, when we consume sugar, the hormone insulin is released which increases the number of channel proteins in our plasma cell membranes, facilitating the movement of sugar from the blood into our cells where it can be used to release energy in the mitochondria.