Renal Acid Base Regulation

The kidneys help to regulate the blood pH by excreting H+ in the urine and by reabsorbing bicarbonate. The H+ enters the filtrate in two ways: by filtration through the glomeruli and by secretion into the tubules. Most of the H+ secretion occurs across the wall of the proximal tubule in exchange for the reabsorption of Na+. This exchange is performed by a transport carrier described as "antiport," because it moves the Na+ and H+ in opposite directions (see chapter 6).

Since the kidneys normally reabsorb almost all of the filtered bicarbonate and excrete H+, normal urine contains little bicarbonate and is slightly acidic (with a pH range between 5 and 7). The mechanisms involved in acidification of the urine and reabsorption of bicarbonate are summarized in figure 17.28.

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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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