Lecture 18: Renal Control of Acid-Base Balance Flashcards
Why is it important to keep the pH at 7.4?
pH changes affects protein structure and function
How do lungs maintain pH?
How do kidneys maintain pH?
Regulating PaCO2 levels levels via respiration (volatile acids)
Regulating [HCO3-] levels via excretion/resorption (fixed acids)
What is a buffer?
Sponge analogy - a molecule that soaks up as much H+ as it can so that blood doesn’t get too acidic/basic too easily
What are the important physiological buffers?
HCO3-
Hb
H2PO4-
NH4+
How does the ionic shift mechanism serve as a buffer?
If ICF or ECF has higher H+, exchange K+ across the membrane to normalize the pH while also balancing the positive charges
Example: If ICF is more acidic than the ECF. ECF gives 1 K+ to ICF in exchange for an H+ from ICF until they normalize.
What is the Henderson Hasselabalch equation?
pH = 6.1 + log (HCO3-)/0.03 pCO2
In the lungs, how can you “edit “ how much your pH changes?
Fasting breathing = bigger pH change
Directly proportional
Why is HCO3- reabsorbed? Where does this happen mostly?
HCO3- is the main buffer so body wants to keep it in the body
Most HCO3- reabsorbed at PCT
Explain how countercurrent multiplier results in concentrated urine
- TAL permeable to NaCl not H2O > salt flows into interstitium
- TDL permeable to H2O > water flows out to dilute the salt
- remaining filtrate at TDL is now more concentrated
- filtrate continues down to loop of Henle and reaches 1200 mOsm
- moves up the TAL to be diluted as NaCl flows back out to repeat the process
- H2O is reabsorbed at the CT/CD, leaving concentrated urine to be excreted out
What are 2 ways the body replenishes its supply of the HCO3- buffer?
Reabsorb and recycle HCO3- from filtrate at the PCT
Generate new HCO3- at collecting duct
How does HCO3- reabsorption happen at the PCT?
- CO2 and H2O converted to HCO3- and H+ in PCT cell by CA
- HCO3- transported to blood while H+ is brought out to the lumen by Na/H antiporter in exchange for Na+
- H+ in lumen reacts with another HCO3- to form H2O and CO2 again, which is transported to PCT
And repeat
How is new HCO3- generated at the CD?
- Intercalated cells at the CD converts CO2 + H2O into HCO3- and H+ using CA
- HCO3- gets transported to blood for buffer use, H+ is transported to lumen and excreted to urine
What is the main problem with generating new HCO3- in the CD?
It dumps H+ in the lumen, and can get too acidic and damage the nephron
How does the body protect the nephron from acidic damage when generating new HCO3-?
Which one is largely used by the body? Why?
- 2 ways: Use NH3+ and Titratable acids (phosphates) as buffers
- Ammonia, since Glu is readily available in body whereas phosphates are limited supply
How does NH3 help the nephron “buffer” the lumen?
How do titratable acids “buffer” the lumen?
NH3 (made from Glu) and combine with H+ in the lumen to form NH4+
HPO4 filtered from blood into lumen and combines with H+ to form H2PO4
Both prevent accumulation of H+ in the lumen
