7. Mechanics of Acid-Base balance Flashcards
(27 cards)
What is the normal plasma pH range?
7.35-7.45
Outside what range of plasma pH is considered incompatible with life?
<6.8
>7.8
What is the urine pH range?
5 - 9
What is the normal extracellular concentration of H+?
40 nmol/L
What can cause metabolic acidosis?
Gain of H+
Loss of HCO3-
What can cause metabolic alkalosis?
Loss of H+
Gain of HCO3-
What controls the PCO2?
Alveolar ventilation
What controls plasma HCO3- concentration?
Renal excretion of H+ and reabsorption of HCO3-
Where does bicarbonate reabsorption take place and which areas reabsorb more bicarbonate?
PCT: 80%
AL of LOH: 10%
DCT: 6%
CD: 4%
Henderson hasselback pH equation including bicarbonate and CO2 and typical values
pH = pK + log [HCO3-]/[CO2] pK= 6.1 HCO3-= 24 mmol/L CO2= 1.2 mmol/L
Describe the davenport diagram
Metabolic alkalosis: HCO3- increases, pH increases
Metabolic acidosis: HCO3- decreases, pH decreases
Respiratory split into chronic and acute
Chronic disorders cross into normal pH as adaptations bring pH back towards normal
Calculate BE if plasma bicarbonate is 34
BE= +10
as normal bicarbonate is 24
Describe the process of excretion of H+ and retention of HCO3-.
H+ reacts with HCO3- in filtrate to form H2CO3
Carbonic anhydrase converts H2CO3 to H2O + CO2
H2O + CO2 are absorbed into the tubular cell and react to form H2CO3
Carbonic anhydrase in the cell converts H2CO3 to H+ + HCO3-
H+ pumped into filtrate via H+ ATPase
Na+ gradient into cells is used to antiport HCO3- into the blood
Name the 2 transporters on the basolateral membrane that allow HCO3- reabsorption
Cl-/ HCO3- exchanger
Na+/ HCO3- cotransporter
What 2 identities can intercalated cells of the CD take?
Alpha: Acid secreting
Beta: Bicarbonate secreting
Describe the mechanisms occurring in an alpha cell of the CD
HCO3- and H+ in filtrate combine
Carbonic anhydrase catalyses formation of water and CO2
CO2 moves into alpha cell, combines with water
Carbonic anhydrase catalyses formation of H+ and HCO3-
Transporters on apical surface drive H+ into filtrate
Cl-/HCO3- exchanger on basolateral membrane allow HCO3- reabsorption
Which 3 transporters on the apical membrane of alpha cells drive H+ back into the filtrate?
Na+/K+ antiporter
H+/K+ ATPase
H+ ATPase
How do the mechanisms in the beta cell differ to that of the alpha cell in the CD?
Mechanisms are the same, just flipped upside down
Bring H+ into body and push HCO3- out
Describe bicarbonate production from AAs
In cuboidal epithelial cells of PCT
AAs e.g. Glutamine split into constituents
The ammonium produced is excreted
HCO3- produced is reabsorbed
What happens to hydrogen phosphate in the filtrate?
When secreting H+, combines with HPO4,2- to form H2PO4-
This is analysable from urine
What movement occurs at the chloride bicarbonate exchanger?
Cl- moves into cell
HCO3- moves out to be reabsorbed
Cl- moves out through channels
Describe the compensatory mechanisms for respiratory acidosis (acute and chronic)
Acute: Intracellular buffering
Chronic: HCO3- generation and increased ammonium excretion
Describe the compensatory mechanisms for respiratory alkalosis (acute and chronic)
Acute: Intracellular buffering
Chronic: decreased HCO3- reabsorption and decreased ammonium excretion
Describe the compensatory mechanisms for metabolic alkalosis
Hypoventilation to decrease CO2 excretion
