Influences Cell Volume Excitability Acid Base Balance and Metabolism

As the major osmotically active solute in cells, the amount of cellular K.+ is the major determinant of the amount of water in (and, therefore, the volume of) the ICF compartment, in the same way that extracellular Na+ is a major determinant of ECF volume. When cells lose K.+ (and accompanying anions), they also lose water and shrink,- the converse is also true.

The distribution of K+ across plasma membranes—that is, the ratio of intracellular to extracellular K+ concentrations—is the major determinant of the resting membrane potential of cells and, hence, their excitability (see Chapter 3). Disturbances of K+ balance often produce altered excitability of nerves and muscles. Low plasma [K+] leads to membrane hyperpolarization and reduced excitability, muscle weakness is a common symptom. Excessive plasma K+ levels lead to membrane depolarization and increased excitability. High plasma K+ levels cause cardiac arrhythmias and, eventually, ventricular fibrillation, usually a lethal event.

K+ balance is linked to acid-base balance in complex ways (see Chapter 25). K+ depletion, for example, can lead to metabolic alkalosis, and K+ excess to metabolic acidosis. A primary disturbance in acid-base balance can also lead to abnormal K+ balance.

K+ affects the activity of enzymes involved in carbohydrate metabolism and electron transport. K+ is needed for tissue growth and repair. Tissue breakdown or increased protein catabolism result in a loss of K+ from cells.

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Essentials of Human Physiology

Essentials of Human Physiology

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.

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