L13 Renal Contribution to Acid/Base Ballance Flashcards
What is acid derived from the hydration of CO2 called?
How is it eliminated?
Volatile Acid
Eliminated Via the Lungs
What is acid derived from the protein metabolism and dietary intake of Sulfates/phosphates called?
How is it eliminated?
Non-Volatile Acid
Kidneys
In order to maintain acid-base balance, the kidney must accomplish what two tasks?
1) Reabsorption of all filtered bicarbonate
2) Excrete the daily non-volatile acid (not derived from hydration of CO2)
How is H+ Excreted?
Hydrogen Ion Secretion: H+ is buffered in the blood, NOT filtered by kidneys as free ions
In the Tubular Fluid Secreted H+:
- Combine with filtered bicarbonate => Bicarbonate Reabsorption
- Combine with urinary buffers to be excreted as ((Titratable Acids and Ammonium**
Segmental Reabsorption of HCO3?
What renal mechanisms come into play to bring pH back to normal when [H+] is elevated?
Cellular Mechanisms for Proximal Tubule H+ and HCO3 Transport?
H+ secretion across apical membrane:
- Primarily via a Na+/H+ antiporter (NHE_3)_
- Via H+ ATPase
Carbonic Anhydrase (CA) plays important role in H+ secretion/HCO3 reabsorption
- Within cells, Carbonic Anhydrase 2 generates H+ and HCO3 from CO2 and H20
- Membrane bound Carbonic Anhydrase 4 produces H20 and CO2 from luminal carbonic acid (H2CO3)
Exit of HCO3 across basolateral membrane:
- Primarily via a Na+/3HCO3 Symporter (NBC1)
- Also via a Cl-/HCO3-antiporter (AE2)
How do Cellular Mechanisms for H+/HCO3 transport by TAL and Early DCT differ from the PCT?
PCT
- H+ secretion across apical membrane occurs primarily via a Na+/H+ antiporter (NHE 3) and via H+-ATPase
- HCO3-reabsorption across basolateral membrane occurs primarily via a Na+/ 3 HCO3-symporter (NBC1) and via a Cl-/HCO3-antiporter
TAL and Early DCT
- H+ secretion across apical membrane occurs primarily via a Na+/H+ antiporter (NHE 2) and via H+-ATPase
- HCO3-reabsorption across basolateral membrane occurs primarily via a Na+/HCO3-symporter (NBC n 1) and via a Cl-/HCO3-antiporter
Type A intercalated cells secrete ____and reabsorb ______
Type B intercalated cells secrete _____ and reabsorb _____
Activity of Type A cells increases when blood _______; activity of Type B cells increases if blood _________
Type A intercalated cells secrete H+ and reabsorb HCO3-
Type B intercalated cells secrete HCO3- and reabsorb H+
Activity of Type A cells (A= ACID) increases when blood academic; activity of Type B (B= BASE) cells increases if blood alkalemia
Cellular Mechanisms for H+ and HCO3 Secretion by Type A Intercalated Cells of the Collecting Duct
H+ secretion across apical membrane occurs by H+/K+ ATPase and H+/ATPase
HCO3-reabsorption across basolateral membrane occurs via a Cl-/HCO3-antiporter (AE-1)
No Na+, K+/ATPase pumps on basolateral side: energy required for transport function of these cells is derived from H+ gradient generated by H+-ATPases on apical side
Aldosterone stimulates H+ ATPase Activity
Cellular Mechanisms for H+ and HCO3 Secretion by Type B Intercalated Cells of the Collecting Duct
H+/HCO3-secretion across apical membrane occurs via Cl-/HCO3-antiporter (Pendrin)
H+ reabsorption across basolateral membrane occurs via ((H+/ATPase((
Titratable Acid vs Ammonium?
A titratable acid refers to any acid that can lose proton(s) in an acid-base reaction
In renal physiology, a titratable acid is a term that refers to non-volatile acids (i.e. phosphoric acid, sulfuric acid) and is used to explicitly exclude ammonium (NH4+)
Ammonium is not measured as part of the titratable acidity because the high pK (pK=9) of ammonium means no H+ is removed from NH4+ during titration to a pH of 7.4
Mechanisms by which tubules add additional HCO3- to plasma?
Reabsorption of filtered HCO3-alone cannot replenish the HCO3-lost during acid neutralization
- PCT production/secretion of Ammonium (NH4+) (Ammonigenesis)- (quantitatively more important): => H+ is excreted, HCO3-is added to the plasma
- In collecting tubule Type A intercallated cells secrete H+ which in the lumen with a buffer other than HCO3- (HPO42-, creatinine, uric acid) => production of “additional” HCO3-for the plasma as CA2 intracellular is able to generate more HCO3
Overall scheme of renal NH3/NH4+ Handling?
Key Point 1: Significant proportion of the NH4+ secreted by _______ is reabsorbed by ____ => ultimately excreted
Key Point 2: NH4+ excretion is ___________ in acidosis
Key Point 1: Significant proportion of the NH4+ secreted by PCT is reabsorbed by TAL => ultimately excreted
Key Point 2: NH4+ excretion is INCREASED in acidosis
__________ stimulates phosphaturia because phosphate serves as a titratable acid buffer. By contrast, __________ increases renal phosphate absorption
Acidosis stimulates phosphaturia because phosphate serves as a titratable acid. By contrast, alkalosis increases renal phosphate absorption