16. Renal Physiology Session 3 Flashcards
What molecules are reabsorbed in the early proximal convoluted tubule?
NaHCO3, NaCl, glucose, amino acids.
K reabsorbed via paracellular pathway.
How is NaHCO3 reabsorbed in the PCT?
Via Na+/H+ exchanger located in luminal membrane of epithelial cells.
What enzyme catalyzes the formation of H2CO3 from CO2 and water and vice versa?
Carbonic anhydrase
It will make H2CO3 in the epithelial cells. It will make CO2 and water in the lumen/urine.
What are the effects of carbonic anhydrase inhibitors?
Decreased H+ formation inside PCT cell Decrease of Na+/H+ antiport Increase Na+ and HCO3 in lumen Increased diuresis Increase urine pH Decrease body pH
What is reabsorbed in the thin descending limb of the loop of Henle?
Water
What is reabsorbed in the thick ascending limb of the loop of Henle?
Na+, K+, 2Cl-, Mg2+, Ca2+
Impermeable to water
How are Mg2+ and Ca2+ reabsorbed?
Increased K+ concentration in cells causes K+ to leak into lumen. This creates a positive potential that drives reabsorption of Mg2+ and Ca2+.
What are the consequences of the inhibition of the luminal Na+/K+/2Cl- cotransporter by loop diuretics?
Decreased intracellular Na+, K+, 2Cl-.
Decreased back diffusion of K+, so less Mg2+ and Ca2+ reabsorbed
Decreased urine pH
Increased body pH
How is NaCl reabsorbed in the DCT?
Na+/Cl- cotransporter (NCC)
How is Ca2+ reabsorbed in the DCT?
Calcium channels
Regulated by parathyroid hormone (PTH)
What are the effects of thiazide diuretics on the DCT?
Inhibits Na+/Cl- cotransporter (NCC)
Decreased urine pH
Increased body pH
Also enhances reabsorption of Ca2+ in both DCT and PCT.
What is the most important site for K+ secretion?
Collecting tubule (CCT)
How is Na+ reabsorbed in the collecting tubule?
Epithelial sodium channel (ENaC)
What are the two mechanisms for K+ sparing diuretics? How does this effect pH?
Inhibition of aldosterone receptor, leading to decreased expression of ENaC
Inhibition of ENaC directly
Both increase urine pH, and decrease body pH (where K+ goes, H+ follows).
Where does the secretion and reabsorption of organic acids and bases occur?
Proximal tubule, straight segments
What effect does ADH have on urea permeability in inner medullary collecting ducts (IMCD)?
It increases its permeability and urea diffuses down the gradient into the interstitium. Shortly after, it encounters the loop of Henle and is diffused back in. The process repeats.
What is ADH’s effect on NKCC2 cotransporter in the TAL?
Increases presence of NKCC2 channels. More Na+, C+, and 2Cl- are reabsorbed.
Why is the entire medullary interstitium kept salty?
The descending limb of the LoH is only permeable to water. The hypertonic medulla is the major driving force of water reabsorption. It stays salty because of the pumps in the ascending limb of the LoH.
How does one calculate free water clearance, C(H2O)?
V - Cosm
V: urine flow rate
Cosm: osmolar clearance
If negative, excess solutes are removed. If positive, more excess water is being removed.
How does one calculate osmolar clearance (Cosm)?
(Uosm x V) / Posm
How does one calculate obligatory urine volume (OUV)?
(minimum solute excretion per day) / (max urine concentrating ability)
What is the key cotransporter located in the thick ascending limb of the loop of Henle?
Na+/K+/2Cl- cotransporter (NKCC2)
What channels do aldosterone act on?
Increases expression of ENaC channels in the collecting tubule.
Also increases basolateral Na+/K+ ATPase.
Where does ADH increase the expression of AQP2 channels?
Collecting tubule
