Magnitude and Direction of Diffusion Diffusion Rate versus Distance Diffusion through Membranes Mediated-Transport Systems
Facilitated Diffusion Active Transport
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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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.