Renal 9 urea, bicarb, buffers Flashcards
No- it is dependent on the development of a favorable concentration gradent and isabsorbed through the paracellular path. 50% is reabsorbed in the porximal convoluted tubule
urea, bicarbonate, and hydrogen
urea transporters
urea, bicarbonate, and hydrogen
critiacal osmol in the medullary interstitium
urea, bicarbonate, and hydrogen
increased nitrogen in the blood
urea, bicarbonate, and hydrogen
1.) Decreased GFR (urea production > urea secretion) 2.) elevated urea production (high protien diet, steroid therapy) 3.) Excessive urea reabsorption in PT (ex: hypovolemia)
urea, bicarbonate, and hydrogen
term typically used to describe pathological increases in urea
urea, bicarbonate, and hydrogen
Can occur in hypovolemic states: GFR falls leading to an increase in plasma creat but there is an increase in reabsorption of Na, other solutes, and water in the proximal tubule die to increased sympathetix activity and increased angiotensin II. BUN increases due to increased GFR and enhanced reabsorption of urea seconday to increased Na and water (development of a more favorable concentration gradient) The Bun: Creat is >20:1 indicating the problem is prerenal
urea, bicarbonate, and hydrogen
GFR falls and there is an increase in BUN and Creat but the ratio remins 10:1
urea, bicarbonate, and hydrogen
both passively (through paracellular route) and actively through the urea transporter
urea, bicarbonate, and hydrogen
1.) increases the permeability to water and urea 2.) stimulates the urea transoprter activity in the medullary collecting duct
urea, bicarbonate, and hydrogen
1.) must excrete an amount of H equal to the daily production of nonvolatile acids 2.) Must prevent the loss of HCO3 in the urine
urea, bicarbonate, and hydrogen
CO2 is blown off during respiration (rate of ventilation determines areterial PCO2)
urea, bicarbonate, and hydrogen
Active process that moves H across the luminal membane into the tubule: H is produced by the reaction between CO2 and water in the lumen, it travels through NHE3 (H transpoter) across the luminal membrane into the lumen(Na moves down its gradient causig secretion of H) . Requires a proton acceptor in the tubular fluid
urea, bicarbonate, and hydrogen
For every proton that gets secreted a bicarbonate gets reabsorbed
urea, bicarbonate, and hydrogen
H-ATPase pump in the luminal membrane of intercalated cells (there also appears to be a K-H-ATPase in the luinal membrane)
urea, bicarbonate, and hydrogen
large lumen negative potential generated by Na reapsorption by principle cells - Coupling between H secretion and Na reabsorption
urea, bicarbonate, and hydrogen
aldosterone stimulates Na reabsorption and therefore increased H secretion and K secretion in intercalated cells
urea, bicarbonate, and hydrogen
H+ is derived pricipally from the hydration of CO2
urea, bicarbonate, and hydrogen
Strong correlation: as PCO2 increase it causes an increase in H secretion
urea, bicarbonate, and hydrogen
Hydrogen secretion
urea, bicarbonate, and hydrogen
4.5 - after this net secretion ceases
urea, bicarbonate, and hydrogen
without proton acceptors secretion would cause a rapid fall in urine pH (due to increased H) and secretion would cease due to back leak of H from the lumen through the tubule and the low lumen pH would inhibit the ATP dependent proton pump. Withough acceptors we wouldnt be able to excrete more than 32 umol H/day (with them we excrete 100,000 umol/day)
urea, bicarbonate, and hydrogen
Bicarbonate (HCO3) - the reaction between secreted H with bicarb normally acomplishes the reabsorption of the entired filtered load of HCO3- (why? Because addition of a hydrogen would allow it to cross the membrane and be reabsorbed )
urea, bicarbonate, and hydrogen
90% reabsorbed in the proximal tubule ( normally the urine is esentially bicarbonate free)
urea, bicarbonate, and hydrogen
Na reabsorption via H+ secretion
urea, bicarbonate, and hydrogen
1.) one Na enters the cell ( Na-H antitransporter) 2.) one HCO3 dissappears from the tubular filtrate 3.) one HCO3 is produced in the cell and reabsorbed (due to CO2 that enters the cell) IN OTHER WORDS: Na enters the cell and H moves into the tubular lumen where it interacts with bicarbonate in the presnce of carbonic anhydrase to form CO2 and H20 (this is the step where bicard disappears) Co2 is then allowed to move into the tubular cel where it interacts to create a bicarbonate that then gets reabsorbed (the HCO3 that is reabsorbed is NOT the same one that was originally in the tubular filtrate
urea, bicarbonate, and hydrogen
present in within the cells and in the brush border of the luminal sufrace of the tubule. Catalyzes the hydration of CO2
urea, bicarbonate, and hydrogen
No Na-H exchanger - relpaced by H-ATPase and H-K ATPase
urea, bicarbonate, and hydrogen
Na-H exchanger
urea, bicarbonate, and hydrogen
not a true transport maximun (because there isnt a transporter) The transport maximum is really a measure of the capacity to secrete H+. Under normal conditions HCO3 is just slightly BELOW the renal threshold
urea, bicarbonate, and hydrogen
phosphate
urea, bicarbonate, and hydrogen
1.) excrete 50-100 mEq of acid in the urine as titratable acid and NH4 each day 2.) produce an equal amount of NEW BICARBONATE in the tubular cells and deliver it to the body fluids
urea, bicarbonate, and hydrogen
these reactions generally occur after most of the major urinary base (HCO3) has been removed from the filtrate. For each mole of H that reacts with NH3 or anouther base in the tubular fluid, one mole of NEW HCO3 is geneated and restored to the body fluid and one mole of H is eliminated in the urine as a nondissociated acid
urea, bicarbonate, and hydrogen
they significantly increase the amount of H that can be secreted while also retoring plasma HCO3 levels
urea, bicarbonate, and hydrogen
it gets largely used up before the minumum urinary pH is achieved (4.5) because its pKa is 6.8 - However, bases with lower pKa can then take over to accept protons
urea, bicarbonate, and hydrogen
equal number of acid and base
urea, bicarbonate, and hydrogen
phosphate (HPO4), urate, creatine, b-hydroxybutyrate (diabetic ketoacidosis), acetoacetat (diabetic ketoacidosis) lactate
urea, bicarbonate, and hydrogen
they are only present in small numbers (or not at all)) and the pHa for some are unfavorable for protonation within the normal range of urinary pH
urea, bicarbonate, and hydrogen
NH3
urea, bicarbonate, and hydrogen
synthysized in tubular cells from glutamine (get 2 NH3 per glutamine) Secreted as NH3 (or NH4+) by all segments of the nephron. NH3 is lipid soluble and secreted by passive diffusion (NH4+ is diffusion trapped)
urea, bicarbonate, and hydrogen
allows for the continued secretion in an cid urine
urea, bicarbonate, and hydrogen
new HCO3 = titratable acid + NH4
urea, bicarbonate, and hydrogen
1.) Availability of urinary base (H+ acceptors) 2.) Changes in aretrial PCO2 (increase PCO2 = Increased H secretion) 3.) Aldosterone excess (can cause hyokalemia or metabilic alkylosis) or deficit (hyperkalemia and metabolic acidosis) 4.) Hyperkalemia (K-H exchange) 5.) Increased Na delivery to the distal nephon (ex: over use of loop or thiazide diuretics - enhanced Na reabsorption leads to H secretion) 6.) Renal tubular acidosis
urea, bicarbonate, and hydrogen
