OBJECTIVE 1: TO REVIEW THE GENERAL FEATURES OF THE BODY
BUFFER SYSTEMS AND TO GAIN A GENERAL UNDERSTANDING OF THEIR INTERACTION
WITH THE KIDNEY.
A. Fig. 9-1 depicts the buffer systems in blood, how these buffer systems react to acid and alkali produced by tissue metabolism, the interrelationships among these buffering system, the excretion of acid and alkali by the kidney, and the excretion of CO2 by the lungs. The two buffer systems are in dynamic equilibrium with the same hydrogen ion concentration (pH), so that a change induced in the concentration of any one factor in either buffer system rapidly affects the other system and a new hydrogen ion concentration in the blood is established. The lungs assist in maintaining a constant blood pH by removing CO2, while the kidney excretes acid in the form of H2PO4 and NH4 and alkali in the form of HCO3.
Fig. 9-1. The acid-base buffering systems of the body. The arrows across the box representing the kidney indicate excretion only. They are not meant to convey any information on the renal mechanism involved.
B. The kidneys correct metabolic disturbances that result from imbalanced food intake or internal metabolic disorders. Normally, in members of a population whose diet contains a significant amount of animal protein, cellular metabolism results in net addition of acid to the blood, approximately 1 mEq/kg body weight/day.
C. The kidneys compensate for respiratory imbalances that result when respiratory disorders alter the rate of ventilation of the lung and subsequently the PCO2 of tissue fluids.
D. Whatever the nature of the disturbance, the response of the kidney leads to the formation and extraction from the plasma of a fluid with an excess or a deficit of acid. The primary result is a return of the H ion concentration of the blood toward the normal level.
E. The primary renal mechanisms involved in acid-base control are:
1. The processes that secrete protons into the tubular fluid.
2. Secretion of HCO3 by the collecting tubule.
3. The manufacture and transport of ammonium.
4. The buffer systems in tubular fluid that react with secreted protons: HCO3-:H2CO3, HPO4=:H2PO4- and NH3:NH4+.
5. The lungs perform the same function of controlling the PCO2 of tubular cells and tubular fluid as they do for other cells and fluids in the body.
QUESTIONS:
1. What are the two major
buffer systems present in the blood? How do they react to the production
of acid by muscle cells? How do the lungs respond? How do they react to
the loss of CO2 during hyperventilation?. How would the buffer systems and
the lungs react to inhibition of acid excretion by the kidney?
2. What are the major renal transport mechanisms
involved in the kidneys=
response to acid base disturbances?
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