Chapter 30 - Regulation of Acid-Base Balance Flashcards
Whys is H+ regulation very precise?
Because the H+ influences almost all enzyme systems in the body.
What is the normal extracellular concentration of H+?
0.00004 mEq/L
What is the definition of a strong acid?
One that rapidly dissociates and releases especially large amounts of H+ in solution
What is the pH range of urine?
4.5 to 8 pH.
What is the normal pH of arterial blood?
7.4 pH.
What is the normal pH of venous blood and interstitial fluid?
7.35 pH.
What are the limits of pH that a person can live for more than a few hours?
6.8 to 8 pH.
What are the 3 primary systems that regulate the H+ concentration in the body fluids?
- Chemical acid-base buffer systems of the body fluids
- Respiratory center
- Kidneys
What is a buffer?
Any substance that can reversibly bind H+.
Describe the bicarbonate buffer system.
A water solution of carbonic acid (H2CO3) and bicarbonate salt (NaHCO3)
How is carbonic acid made in the body?
CO2 + H2O + Carbonic anhydrase
What is the dissociation constant K?
For any acid, the concentration of the acid relative to its dissociated ions
Which system has primary control of the bicarbonate concentration?
Kidneys
Which system has primary control of the PCO2 in the extracellular fluid?
Rate of respiration
What is the difference between a metabolic acidosis and respiratory acidosis?
Metabolic acidosis = decrease in [bicarbonate]
Respiratory acidosis = Increase in [PCO2]
What is the role of the phosphate buffer system?
It plays a major role in buffering renal tubular fluid and intracellular fluids
How do the changes in extracellular pH change the intracellular pH?
The diffusion of the bicarbonate buffer system thru the cell membrane
How do the kidneys regulate extracellular fluid H+ concentration?
- Secretion of H+
- Reabsorption of filtered HCO3-
- Production of new HCO3-
Where does most of the bicarbonate reabsorption and H+ secretion take place in the kidney?
80-90% in the proximal tubule
How are hydrogen ions secreted in the kidneys?
- Thru the sodium-hydrogen counter-transport in the cells of the proximal tubule.
- Thru the active hydrogen pump of the intercalated cells of the late distal and colleting tubules.
How much H+ is secreted in a day?
4400 mEq/day
How is bicarbonate reabsorbed?
Indirectly. First combines w/ H+ to form H2CO3 which becomes CO2 + H20. The CO2 easily moves into the tubular cell, which combines w/ water and carbonic anhydrase to form H2CO3 again. Then it dissolves into HCO3- and H+ again (this is all happening inside the cell). The H+ is secreted while the HCO3 is absorbed into the bloodstream.
How is the bicarbonate expelled from the tubular cell into the bloodstream?
By Na+ _ HCO3 cotransport and Cl- _ HCO3- exchanger.
How much HCO3- is filtered per day?
4320 mEq/day
What happens whenever an H+ secreted into the tubular lumen combines w/ a buffer other than HCO3-?
A net gain of a new HCO3- to the blood.
What happens whenever a NH4+ is excreted?
A new HCO3- is generated and added to the blood.
What is the dominant mechanism by which acid is eliminated in chronic acidosis?
Excretion of NH4+
What are the most important stimuli for increasing H+ secretion by the tubules in acidosis?
- Increase in PCO2 of the extracellular fluid.
2. Increase in H+ concentration of the extracellular fluid (decrease in pH).
What values should we expect to increase/decrease in a simple respiratory acidosis after partial renal compensation?
Reduced plasma pH
Increased CO2
Increased HCO3-
What values should we expect to increase/decrease in a simple metabolic acidosis after partial respiratory compensation?
Low pH
Low HCO3-
Low PCO2
What values should we expect to increase/decrease in a simple respiratory alkalosis after partial renal compensation?
Increased pH
Decreased PCO2
Decreased HCO3-
What values should we expect to increase/decrease in a simple metabolic alkalosis after partial respiratory compensation?
Increased pH
Increased HCO3-
Increased PCO2
