ACID BASE BALANCE Flashcards
(35 cards)
non-volatile (fixed) acid
acids that are normally produced during normal metabolic processes in the body or excreted
- cannot be eliminated by ventilation via the lungs
examples of nonvolatile acids
lactic acid, sulfuric and phosphoric acids, keto acids, uremic acids
sources of nonvolatile acids
anaerobic glycolysis (lactic acid), fatty acid oxidation (ketone production), amino acid metabolism, nucleic acid oxidation, fecal base loss
T or F: CO2 is a nonvolatile acid
FALSE
volatility
describes how easily a substance will vaporize
which source of acid is produced in greater amounts in the body?
nonvolatile
- nonvolatile ~50-100mmoles/day
- volatile 15-20 mmoles/day (want this to be low)
normal concentration of bicarb in the blood?
24 mM
role of the kidney in acid-base balance
1- prevent bicarb loss (by reabsorbing ALL bicarb that is freely filtered and replenishing bicarb that was consumed from buffering fixed H+)
2- excrete acid equal to nonvolatile acid production (~50-100mEq/day)
How is bicarb reabsorbed at the PT?
NHE at the proximal tubule reabsorbs Na+ and exchanges for H+ to the ECF
- the H+ binds bicarb –> carbonic acid and carbonic anhydrase converts to CO2 and H2O which can freely enter the cell
- carbonic anhydrase in the cell converts CO2 and H2O to bicarb
- bicarb is shuttled into the blood by a NBCe1 transporter on the BASOLATERAL membrane
NBCe1 transporter
Na+/HCO3- cotransporter 1
- transporter on the BASOLATERAL membrane of tubular cell that shuttles bicarb back into the blood from the kidney
what affect does angiotensin 2 have on the NHE at the proximal tubule?
upregulates the NHE at the proximal tubule to further regulate acid/bicarb balance
where does most bicarb get reabsorbed and why?
at the proximal tubule (~80% bicarb reabsorption)
how much bicarb is reabsorbed at the TAL and DT?
10% and 6% respectively
alpha intercalated cell
cell of the collecting duct that secretes acid and reabsorbs bicarb to maintain acid-base homeostasis
- secretes H+ into the filtrate where buffers (HPO3- and NH3) are present to titrate and form titratable acids in the urine before excretion
intercalated beta cell
cell of the collecting duct that is typically only active during periods of alkalosis
(i.e vomiting)
- secretes bicarb
- has Pendrin transporter to move bicarb into the tubular fluid and returns H+ back into the blood to restore pH
2 major buffers of the kidney
phosphate and ammonium
titratable acid
acid that can pick up free H+ of the acid load
Phosphate as a urinary buffer
titrates free H+ in the filtrate after alpha intercalated cell secretes it
- 1/3 of the acid load
Ammonia as a urinary buffer
titrates free H+ in the filtrate after alpha intercalated cell secretes it
- 2/3 of the acid load
why are urinary buffers critical?
prevents the urine from being too acidic, which would compromise the ability of the kidneys to function
- without buffers, free H+ would be traveling through the kidneys
what is the source of ammonia used to titrate acid in urine?
metabolism of glutamine
where is NH3/NH4+ reabsorbed and secreted?
reabsorbed in TAL and secreted in CD
- H+ is also secreted at CD –> NH4+ excreted in urine
How does the kidney respond to acid loads?
1- reabsorbs ALL bicarb
2- increases H+ excretion in form of titratable acids
3- produces more NH4+
- these are done via enzyme synthesis, transporter regulation etc
what is the minimum pH of urine?
4.5; kidneys can only excrete nanomolars of acid without causing kidney damage
- the kidneys excrete 50-100mEq of acid/day in the form of titratable acids which would not be possible without buffering the H+ with nonvolatile acids
