The Kidneys Normally Maintain K Balance

Figure 24.14 depicts K+ balance for a healthy adult man. Most of the food we eat contains K+. K+ intake (50 to 150 mEq/day) and absorption by the small intestine are unregulated. On the output side, gastrointestinal losses are normally small, but they can be large, especially with diarrhea. Diarrheal fluid may contain as much as 80 mEq K+/L. K+ loss in sweat is clinically unimportant. Normally, 90% of the ingested K+ is excreted by the kidneys. The kidneys are the major sites of control of K+ balance; they increase K+ excretion when there is too much K+ in the body and conserve K+ when there is too little.

Abnormal Renal K+ Excretion. The major cause of K+ imbalances is abnormal renal K+ excretion. The kidneys may excrete too little K+; if the dietary intake of K+ continues, hyperkalemia can result. For example, in Addison's disease, a low plasma aldosterone level leads to deficient K+ excretion. Inadequate renal K+ excretion also occurs with acute renal failure; the hyperkalemia caused by inade-

Input

Ingested K+ 100 mEq/day

Bone, dense connective tissue cartilage K+ 300 mEq

Transcellular fluid K+ 40 mEq

Bone, dense connective tissue cartilage K+ 300 mEq

Extracellular fluid K+ 60 mEq

Intracellular fluid K+ 3,300 mEq

Transcellular fluid K+ 40 mEq

Extracellular fluid K+ 60 mEq

Intracellular fluid K+ 3,300 mEq

Output

Urinary K+ excretion 90 mEq/day

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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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