Cell Membranes

Diffusion

Magnitude and Direction of Diffusion Diffusion Rate versus Distance Diffusion through Membranes Mediated-Transport Systems

Facilitated Diffusion Active Transport

Osmosis

Extracellular Osmolarity and Cell Volume Endocytosis and Exocytosis

Endocytosis Exocytosis

Epithelial Transport

Glands

SUMMARY KEY TERMS REVIEW QUESTIONS THOUGHT QUESTIONS

Vander et al.: Human I I. Basic Cell Functions I 6. Movement of Molecules I I © The McGraw-Hill

Physiology: The Across Cell Membranes Companies, 2001

Mechanism of Body Function, Eighth Edition

As we saw in Chapter 3, the contents of a cell are separated from the surrounding extracellular fluid by a thin layer of lipids and protein—the plasma membrane. In addition, membranes associated with mitochondria, endoplasmic reticulum, lysosomes, the Golgi apparatus, and the nucleus divide the intracellular fluid into several membrane-bound compartments. The movements of molecules and ions both between the various cell organelles and the cytosol, and between the cytosol and the extracellular fluid, depend on the properties of these membranes. The rates at which different substances move through membranes vary considerably and in some cases can be controlled—increased or decreased—in response to various signals. This chapter focuses upon the transport functions of membranes, with emphasis on the plasma membrane. There are several mechanisms by which substances pass through membranes, and we begin our discussion of these mechanisms with the physical process known as diffusion.

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Essentials of Human Physiology

Essentials of Human Physiology

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