Acid-base balance Flashcards
What is an acid?
A substance that dissociates to release hydrogen ions, thereby reducing pH.
What is a strong acid?
An acid that dissociates completely, e.g. hydrochloric acid (Hcl)
What is a base?
A substance that dissociates to release hydroxide ions or to “tie up” H+ ions, thereby increasing pH.
What do buffer systems in bodily fluids generally consist of?
Combination of a weak acid and the anion released by its dissociation, which functions as a base.
What happens when:
a) acid is added to the buffer system (H+ ions)
b) base is added to the buffer system
a) the anion “mops up” the excess hydrogen, forming more of the weak acid
b) base “ties up” the hydrogen ions; more of the weak acid dissociates to increase the number of H+ ions
What does the Henderson-Hasselbach equation describe?
Useful for estimating the pH of a buffer system:
pH=pK + log [A-]/[HA]
where pK is the dissocation constant of the acid
What is the main physiological buffer system?
The carbonic acid-bicarbonate buffer system
How does the carbonic acid-bicarbonate buffer system protect against decreases in pH?
Addition of hydrogen ions shifts the equilibrium; more carbonic acid is formed, which in turn dissociates into carbon dioxide and water. The carbon dioxide is excreted.
How is precise control of blood pH generally achieved?
The lungs control PC02; the kidneys control bicarbonate
What is the ability to buffer acids limited by?
The availability of bicarbonate ions
What two processes form the kidneys ability to regulate bicarbonate?
The ability to control reabsorption of bicarbonate, and the ability to generate “new” bicarbonate if the bicarbonate reserve is low
When bicarbonate in the tubular fluid is low, what other organic compounds can act as a buffer to “mop up” excreted H+ ions in the urine?
Ammonia and phosphate- acid can be therefore secreted as “acid phosphate” and ammonium ion
What three things does acid secretion by the tubule achieve?
- Reabsorption of bicarbonate
- Formation of acid phosphate (and “new” bicarbonate)
- Formation of ammonium ion (and “new” bicarbonate)
