Acid-base Balance Flashcards
What is the physiological reference range for pH
Between 7.35-7.45
What are the two things that challenge the body systems maintained of the physiological reference range
Production of CO2: oxidative metabolism
13000-15000 mmol co2/day
Acid production: dietary phosphoproteins and sulphur containing proteins
50-100mmol H+ a day
Co2 is produced
Cells and tissues
Co2 removal from cells and tissues from cell -> plasma -> erythrocytes
Cell Co2--> plasma Co2--> erythrocytes In the erythrocytes Co2 combines with H2O in the presence of carbonic anhydrase to form H+ and HCO3- HCO3 --> plasma swapping with Cl- H+ combines with HBO2 Displaces the O2 from the Hb O2 goes into the cells H+ and Hb combine
Co2 removal at the lungs
Lungs O2 –> plasma O2 –> erythrocytes
O2 displaces H+ from Hb
O2 and Hb combine
H+ reacts with HCO3 which has swapped with Cl- to enter from the plasma
H+ and HCO3 combine in the presence of carbonic anhydrase and produce Co2 and H2O
Co2 them leaves the erythrocytes entering the plasma and then entering the lungs to leave to body
How are the hydrogen ions metabolised
Extracellular buffering and respiratory compensation
Extracellular buffers
Bicarbonate, phosphate, proteins
Renal excretion of H+ and retention of HCO3
Renal buffering what happens to the H+ and how does the HCO3 get regenerated
Distal renal tubule cell
Co2 removed from the peritubular plasma into the distal renal tubule cells here it reacts with H2O in the presence of carbonic anhydrase to make H+ and HCO3-
The HCO3 goes into the peritubular plasma
The H+ moves into the tubular fluid and is buffered by ammonia and phosphate ions
Simplified Henderson hasselbach equation
pH = HCO3/pCO2
How can acidosis arise
Fall in HCO3 with normal PCO2
Rise in PCO2 with normal HCO3
How can alkalosis arise
Rise in HCO3 with normal PCO2
Fall in PCO2 with a normal HCO3
How does compensation happen
Disease process alters the concentration of one of the components the ratio and therefore pH can be returned to normal if the other component concentration is sufficiently altered in the same direction
PH return to normal compensation has occurred
Complete if pH restored and partial if pH near normal
What is the expected compensating response in metabolic acidosis
Compensation takes 12-24 hours
Mechanism: respiratory stimulation –> Dec pCO2
Metabolic acidosis Dec HCO3 retention
Need to remove more PCO2
Need to Dec PCO2 by 0.75-0.8 kPa for every 4mmol of Dec HCO3 retention
Expected compensation for metabolic alkalosis
Compensation takes 12-24 hours
Mechanism: respiratory depression so inc PCO2 conc
PCO2 needs to inc by 0.5kPa for every 4mmol/L of inc HCO3
Expected compensating response for respiratory acidosis
compensation take 2-4 days
Mechanism is renal compensation by inc HCO3 conc
Inc HCO3 by 3mmol/L for every 1kPa of inc pCO2
Expected compensatory response for respiratory alkalosis
Compensation 2-4 days
Mechanism renal compensation by Dec HCO3
Need to be HCO3 by 1.5 mmol/L for every 0.4kPa
