Content area
Full text
Because maintaining a normal body pH is essential to the efficient functioning of many physiologic processes, the body has a number of mechanisms that prevent pH fluctuations. Some of these prevent minute-to-minute pH fluctuations over the course of the day, whereas others maintain pH balance from day to day. The kidney plays a key role in both processes. The renal process of bicarbonate reclamation prevents the loss of bicarbonate in the urine and, thus, maintains plasma levels of one substrate that is instrumental to preventing minute-to-minute pH fluctuations. The other renal process, bicarbonate regeneration, replenishes the body's supply of bicarbonate and, thus, maintains pH balance on a day-to-day basis. This article will discuss basic principles of acid-base physiology, the mechanisms that prevent fluctuations in body pH, and the renal processes involved in maintaining a homeostatic pH environment.
Goal:
Discuss the basic principles of acid-base physiology and the mechanisms that prevent fluctuation in body pH.
Objectives:
1. Identify and explain the role of three buffer systems that maintain body pH.
2. Describe a major difference between the bicarbonate reabsorption and generation processes.
3. Discuss the mechanism by which renal processes adapt to changes in daily metabolic acid production.
This article, a continuation of the renal physiology series being published in the Nephrology Nursing Journal, covers renal acidification and is divided into two major sections. The first section reviews principles of acid-base physiology, describing pH and hydrogen ions, buffer systems, and intracellular and extracellular buffering mechanisms. The second section discusses the renal contribution to maintaining pH balance and describes: (a) the reabsorption of filtered bicarbonate, (b) the regeneration of bicarbonate, (c) how hydrogen ion balance is maintained over a 24-hour period, and (d) adaptations that occur in response to changes in the daily acid load.
Principles and Definitions: Acid-Base Physiology
The normal free hydrogen ion concentration in the plasma is 0.000035 - 0.000045 mEq/L. Because this concentration is so low, pH is used to describe it. pH is the negative logarithm of the free hydrogen ion concentration, shown as pH = -log [H+]. Thus, hydrogen ion (H+) concentration defines the pH of a solution. Only free hydrogen ions, also called protons, contribute to the measured pH. If hydrogen ions are bound to other ions (such as...