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25 Cards in this Set
- Front
- Back
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Describe the mechanism for reabsorption of filtered bicarbonate.
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1) H+ secreted from early proximal tubular cells into lumen
2) that H+ combines with filtered bicarb in lumen to make a transient H2CO3 3) this CA dissociates into CO2 + H20 via luminal carbonic anhydrase 4) that CO2 is transferred back into the cell 5) it combines with water to make another transient acid molecule 6) another CA intracellular now acts to dissociate this acid into bicarb and H 7) H goes back to the cycle to caputure another lost HCO3 and the HCO3 in the cell goes into the peritubular capillary |
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What are the 3 roles of the kidney in acid base balance?
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1) resorb bicarb w/o resorbing H+
2) excrete H as titratable acid via secretion of H and synthesis of new HCO3 3) excretion of H as NH4+ with secretion of H and reformation of bicarb |
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How much filtered HCO3 is resorbed?
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around 99% basically almost all
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What are the key points about HCO3 resorption?
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1) net resorption of NaHCO3 without
2) no secretion of H occurs 3) little change of pH of proximal tubular fluid because of luminal CA |
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What influences the resorption of filtered HCO3? (5)
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1) Angiotensin II
2) arterial pCO2 3) Plasma [Cl] 4) Filtred HCO3 load 5) ECF volume |
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How does filtered HCO3 load influence HCO3 resorption?
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you resorb as much as you filter up to 40mEq/L then you have to start excreting HCO3 into the urine
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How does volume contraction and expansion influence HCO3 resorption?
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volume contraction - influences HCO3 resorption because it increases the starling force for reabsorption by decreasing the peritubular capillary hydrostatic pressure and increasing the oncotic pressure
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How does angiotensin II influence HCO3 resorption?
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by stimulating Na H exchange, more H means increased ability to resorb more bicarb
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What two factors come together to contribute to contraction alkalosis?
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1) volume contraction and starling forces
2) angiotensin II |
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How does arterial pCO2 influence HCO3 resorption?
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1)PaCO2 causes more H ions so it would cause more HCO3 resorption
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How does plasma Cl concentration influence HCO3 resorption?
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more CL you have less HCO3 you have
so when you increase Cl you decrease plasma HCO3 so you decrease filtered load and decrease resorption |
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What is the titratable acid that is produced when you are trying to get rid of acid?
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phosphoric acid H2PO4
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Please tell me the steps of making phosphoric acid to excrete excess H+?
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1) H+ is made when intracellular H2CO3 is made by CA and then dissociates
2) the HCO3 is resorbed and the H+ is secreted into the lumen 3) H+ is secreted into the lumen 4) H+ combines with filtered HPO4 to make phosphoric acid 5)H2PO4 is secreted |
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What are the influences on the process of making H+ into excess Phosphoric acid ie. titratable acid?
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1) amount of HPO4 filtered
2) pK of urinary buffer |
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What is the minimum pH value for urine?
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4.4
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What is the ideal urinary buffer range?
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PH of tubular fluid is within 1 unit of buffers pK
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What is the way that the majority of H+ is excreted?
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NH4+
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Where are the three places that the NH4+ excretion occurs?
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1)proximal tubule
2) thick ascending limb of the Loop of Henle 3) intercalated cells of the collecting duct |
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What are the steps of NH4+ excretion?
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1)NH3 is made from glutanmine
2) NH3 is converted to NH4 in the cell 3) NH4 is secreted into lumen by Na H exchanger 4) for every NH4 secreted one new HCO3 is resorbed 5) Some is excreted in urine 6) The rest travels to the TAL where it subs for K on the 3 ion co Xporter and goes to the interstitum 6) NH3 diffuses down its concentration gradient into CD lumen 7) in CD lumen it finds a H+ to combine with 8) now its trapped in CD lumen bc its NH4+ is not lipid soluble 9) excreted |
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What is the effect of lowering the pH on NH4 excretion?
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NH4 form perdominates helping the gradient in the CD
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Is there an increase in NH3 synthesis in respiratory and metabolic acidosis?
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yes but its for chronic/its been a few days
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What is the effect of blood [K] on NH3 synthesis?
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-hyperkalemia inhibits NH3 syntehsis and decreases H+ excretion
-Hypokalemia increases NH3 synthesis and increases H+ secretion |
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In a normal healthy person what is the NH4 vs titratable acid excretion?
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much more H is secreted as NH4+
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What is the H+ secretion situation in DKA?
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1) increase in H+ excretion as NH4
2) elevated excretion of titratable acid using beta hydroxybutyrate as a buffer |
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what is the situation of H+ secretion in chronic renal disease?
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decrease in ability to excrete H+ causing renal tubular acidosis (which is a type of metabolic acidosis)
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