Lecture 19, acid bases Flashcards
Bicarbonate buffer system uses what acid/bases?
- H2CO3
- NaHCO3
- use of carbonic annhydrase
Where can extra HCO3 be excreted from the body?
Kidneys
What is the net result of the combination of CO2 and H2O?
- increased levels of CO2 have the potential to decrease the pH of the blood.
What is the overall effect of lowering the CO2 blood concentration?
- decreased blood CO2 leads to decreased respiratory rate as there the blood pH will be more alkolitic.
- Therefore is [CO2] blood is decreased the CO2 blow-off will be decreased
The major function of the bicarbonate buffer system is what?
-control the levels of bicarb and [H]
What organs help control the bicarbonate buffer system?
- kidneys (bicarbonate concentration)
- lungs (control the pCO2)
Metabolic acidosis disorder is characteristic of what?
- decreased HCO3
Respiratory acidosis occurs how and where?
-from the lungs with increased levels of pCO2
Where does the phosphate buffer system have a major role?
-the renal tubular fluid and intracellular fluids
Why is the phosphate buffer system important in the kidney tubular fluids?
- higher concentration in the tubules
- the lower pH of the tubular fluids allows for a better operating environment for the buffer system
What is the overall net reaction result of the phosphate buffer system?
-strong acid is replaced by additional amounts of weak acid and a salt. Resulting in minimal pH change
What three ways can the kidneys regulate the extracellular H ion?
- reabsorb filtered bicarbonate ion
- secrete H ion
- produce new bicarbonate ions, that would be later reabsorbed
How is bicaronate reabsored into the renal insterstitial fluid and ultimately into the blood stream?
- NzHCO3 combines with H ion, to form H2CO3 and is broken down into CO2 and H2O
- CO2 and H2O is passively absorbed across the membrane, carbonic annhydrase converts the reactants into H2CO3 and breaks down into HCO3 and H ion.
- forming a cyclical pattern to absorb HCO3 and the H ion can move out of the cell via the Na-H exchanger to produce more carbonic acid in the tubular lumen
Where in the nephron does H ion secretion and HCO3 reabsorption occur?
- H ion secretion occurs as secondary active transport except in the descending/ascending thin limbs of henle loop
- active H ion begins in the late distal tubule in the intercalated cells
- 80-90% of bicarbonate reabsorption occurs in proximal tubule
What process occurs in metabolic acidosis in the kidneys?
-regulation to correct the decreased pH, by reabsorbing bicarbonate and secreting new bicarbonate ion into the blood tissue.
What happens in metabolic alkalosis in the kidneys?
-bicarbonate ions are quickly removed from the extracellular fluid, via renal excretion
What is the 2-step process of H ion secretion by the intercalated cells?
- dissolved CO2 in intercalated cells combine with water and form carbonic acid
- carbonic acid dissociates into bicarbonate, becomes rapidly reabosorbed into blood, and H ion is secreted, by H-ATPase into tubular lumen.
What is the best way to describe the incomplete titration?
-There is not a one-to-one amount of ions being absorbed an secreted
What is the minimun amount of pH that the kidneys are able to achieve?
4.5
It is important to allow large amounts of H ion to be excreted, why?
the amount of nonvolatile acid from metabolism would lead to 2667 L of urine a day, if the H ion remained in free solution
How are excess H ions eliminated?
- as bicarbonate ion is formed the H ion is secreted into the lumen by Na-H antiporter.
- H ion binds with phosphate or ammonia to be excreted in urine
- bicarbonate ion is absorbed into the blood as a “new” ion
The phosphate buffer system does what?
Increases the pH of the blood.
- removes H ion from the blood to help form phosphate components, that produce NEW bicarbonate ion that can be secreted into the blood.
- -loss of blood [H] and increase of blood [HCO3]
How can the kidneys correct for alkalosis?
-failure to reabsorb the filtered bicarbonate ion which will lead to decreased blood pH
What process occurs with increased levels of CO2?
-respiratory acidosis
What occurs with decreased levels of bicarbonate ions?
Metabolic acidosis
What is the primary compensating response for respiratory acidosis?
-Increase the plasma concentration of Bicarbonate, initially via the kidney.
Metabolic acidosis is compensated by what function?
- the lungs increase ventilation
- the kidneys can also begin to form new bicarbonate ion to extracellular
When does respiratory alkalosis occur? And what process begins to compensate for it?
- decrease in [CO2]
- caused by hyperventilation
- -reduce plasma HCO3 by increased secretion into tubular lumen
Metabolic alkalosis occurs with what and is compensated how?
- increased plasma [HCO3]
- -compensated by decreasing ventilation and increasing bicarbonate ion secretion into the tubular lumen
What are two buffer systems in the body, and what else can function as a buffer?
- bicarbonate
- phosphate
- proteins act as buffers
What buffer system is the most important buffering system in the renal tubular fluid?
-phosphate buffer system as it is closer to the optimal operating pH.
Compounds that dissociate incompletely into H ions and conjugate base are members of what compounds?
- Weak acids, incompletely dissociate
- Strong acids completely dissociate
The bicarbonate buffer system consists of a bicarbonate buffer salt and what other component?
-weak acid
Primary active H secretion uses H ATPase and occurs in what part of the renal tubules?
late distal tubules with intercalated cells
Most bicarbonate reabsorption occurs in what part of the renal tubule?
- proximal tubule
What occurs with a decrease in bicarbonate ion and results in the decrease in the ratio of bicarbonate ion to carbon dioxide in the extracellular fluid?
- Metabolic Acidosis
- -as the bicarbonate ion level is being decreased
Respiratory alkalosis due to a decrease in CO2 caused by hyperventilation is compensated for by what mechanism?
- renal excretion of bicarbonate ion
What is the effect of Glutamine if it is absorbed into the tubular cells?
- glutamine degrades into 2 ammonium ion and 2 bicarbonate ion.
- new bicarbonate is reabsorbed
- ammonium secreted by Na anti porter
- ultimately buffers the H ion concentration
What does “new bicarbonate ion” refer to?
-production of excess bicarbonate in the tubular cells, as H ion is forced to combine with phosphate or ammonia in the lumen
