Acid Base Homeostasis Flashcards
What contributes to the daily acid challenge?
Carbonic acid build up during metabolism Lactic acid build up from anaerobic respiration Ketoacids from incomplete fat metabolism Fat and protein breakdown Fixed acids in the system
What challenge does diarrhoea pose to acid-base homeostasis?
Excessive bicarbonate excretion leads to metabolic acidosis
What challenge does diabetes mellitus pose to acid-base homeostasis?
Excessive production of ketoacids leads to metabolic acidosis
What challenge does vomiting pose to acid-base homeostasis?
Loss of stomach acid leads to metabolic alkalosis
What challenge does renal failure pose to acid-base homeostasis?
Inability to secrete protons leads to metabolic alkalosis
What challenge do ventilatory disorders pose to acid-base homeostasis?
Respiratory acidosis or alkalosis
What are the three methods of compensation for acid-base challenges? What are their relative speeds?
Bicarbonate, protein and phosphate buffering - fast
Respiratory compensation - fast, but partial
Renal compensation - slow and steady
What are the five steps of renal compensation?
Proton and bicarbonate secretion Bicarbonate retention Bicarbonate production Ammonia excretion Buffer regulation
What is the significance of the pH value 4.5?
The urine pH limit is 4.5
Once pH is 4.5, no more proton secretion will occur
Describe proton secretion in the proximal tubule
Na/K/ATPase sets up a sodium and potassium ion concentration across the basolateral membrane
Sodium is brought into the cell from the tubule in exchange for protons
Potassium leaves via the basolateral membrane alongside chloride which creates a chloride concentration gradient
Protons in the cell are converted to anions
Chloride is brought in from the tubule in exchange for H anions
Describe proton secretion in the collecting duct
Carbonic anhydrase converts water and carbon dioxide into proton and bicarbonate
The proton is pumped out via K/H/ATPase and H/ATPase
The proton is combined with bicarbonate in the lumen via carbonic anhydrase
Describe bicarbonate secretion in the collecting duct
Carbonic anhydrase produces bicarbonate which is exchanged for chloride
Describe the process of ammonium excretion
Glutamine is converted into ammonium ion
The ammonium is either converted into ammonia and diffuses passively or exchanged for sodium
A Na/H exchanger pumps protons out of the cell
Ammonia in the lumen is bound to a proton making an ammonium ion which is now trapped in the lumen to buffer the urine
How does phosphate buffer the urine?
Phosphate absorbs hydrogen ions at low pHs
What causes respiratory acidosis?
Carbon dioxide retention
