3 week 18 Flashcards
what is pH? what is normal arterial plasma pH?
- measure of hydrogen ions
- 0.00004 mM or 7.35-7.45
what pH is considered acidosis? alkalosis?
- pH less than 7.35 = acidosis
- pH greater than 7.45 = alkalosis
why can a change in arterial blood pH have profound effects on body function?
because it alters the pH of fluids throughout the body
what are the sources of H+ and main ways to remove it from the body?
- input: diet, metabolism
- output: kidneys, lungs
decrease in CO2 = ____ in hydrogen ions, ___ing pH
decrease, increasing
what are 3 ways to regulate pH? how long does each way take?
- buffering of hydrogen ions (quickest)
- respiratory compensation (minutes)
- renal compensation (hours to days)
what are the most common ICF buffers? ECF?
- ICF buffers = proteins, phosphates
- ECF buffer = bicarbonate
what effect does increased ventilation have on CO2 and pH? what about decreased ventilation?
- increased ventilation = decreased CO2 (increased pH)
- decreased ventilation = increased CO2 (decreased pH)
how do decreases in plasma pH increase ventilation?
- decrease in plasma pH (+acidity) is detected by peripheral and central chemoreceptors
- chemoreceptors increase ventilation which decreases plasma CO2
- decrease in plasma CO2 = increased pH
what are the 2 key steps of renal regulation
- regulate excretion of hydrogen ions and bicarbonate in urine
- regulate synthesis of new bicarbonate in renal tubules
what happens at the proximal tubule vs the distal tubule/collecting duct?
- PROXIMAL TUBULE
- bicarbonate reabsorption coupled to hydrogen ion secretion
- …
- DISTAL TUBULE/COLLECTING DUCT
- acidosis: secretion of hydrogen ions + synthesis of new bicarbonate ions
- OR
- alkalosis: secretion of bicarbonate + reabsorption of hydrogen ions
describe the details of how bicarbonate reabsorption is coupled to hydrogen ion secretion (3)
- filtered bicarbonate combines with secreted H to form carbonic acid, which is converted to water and CO2 by carbonic anhydrase on the apical membrane.
- CO2 diffuses into epithelial cell, where intracellular carbonic anhydrase catalyzes the conversion of CO2 and water to carbonic acid; the carbonic acid then dissociates into bicarbonate and H.
- H ions are secreted by countertransport with Na ions, whereas the bicarbonate is reabsorbed by cotransport with Na and by countertransport with Cl.
describe the details of bicarbonate production and hydrogen secretion by glutamine metabolism? when does this occur? (4)
- occurs in proximal tubule when acidosis is severe.
- glutamine is catabolized to bicarbonate ions + ammonia.
- bicarbonate ions are transported into peritubular fluid by a Na+/HCO3 cotransporter or a HCO3/Cl countertransporter.
- ammonia binds a H ion to form ammonium, which is secreted by countertransport with Na ions.
describe the details of what happens during acidosis in the distal tubule/collecting duct (3)
- RE: bicarbonate synthesis + hydrogen ion secretion
- carbonic anhydrase in the cytosol converts CO2 into carbonic acid, which dissociates into H ions and bicarbonate ions.
- the H ions are secreted by a H pump or a K/H countertransporter; the bicarbonate ions are transported into the peritubular fluid by a HCO3/Cl countertransporter.
describe the details of what happens during alkalosis in the distal tubule/collecting duct (3)
- RE: bicarbonate secretion and hydrogen ion reabsorption
- bicarbonate ions are secreted into the tubular fluid by type B intercalated cells in the collecting duct.
- H-ATPase pump pumps H ions into the peritubular fluid.
