Renal Physio 8 Flashcards
What is normal acid-base status of the body?
Plasma pH close to 7.4 (range 7.35 – 7.45)
[HCO3-]p close to 25 mmol/l (range 23 – 27)
Arterial PCO2 close to 40 mmHg (range 35 – 45)
What is the first barrier to a chnage in acid base balance?
the buffer system
When is a person said to be acidotic?
pH <7.5
When is a person said to be in alkalosis?
pH >7.5
What happens if there is a change in the acid-base balance?
- Compensation: restore to the pH to 7.4 ASAP
2. Correction - restoration of pH and HCO3 and pCO2 to normal
How sare A-B disturbances classified qas?
Respiratory
metabolic
(acidosis and alkalosis in both)
What is the immediate buffering of a pH change?
Immediate dilution of the acid or base in ECF
Blood buffers (i.e. Hb, HCO3-. Acidosis would reduce [HCO3-]p)
deoxygentated blood has a higher affinity for H+ ions than Oxygenated blood
replenish the buffer stores as they deplete quickly
What regulates the concentration of the bicarbonates in the blood?
Kidney
What aregulates the pCO2 in body?
Respiratory system
What can be used to measure the pH and PCO2?
blood-gas analyser
What is the henderson-hasselbach equation
pH [HCO3-]
[CO2]
Davenport diagram
concentration of bicarbonate - y
pH of plasma - x
Causes of repsiratory acidosis
chronic bronchitis
chronic emphysema
airway restriction (bronchial asthma, tumour)
chest injuries
respiratory depression - morphine/ general anesthesia
What is respiratory acidosis?
Retention of CO2 by the body
–> increased formation of carbonic acid –> excess of free H+ ions
What happens if you have an increased concentration of CO2?
increase in plasma con of H+ and HCO3-
but the pH decreases becuase the HCO3 is formed by the same reaction that causes the acidosis and hence they can’t compensate
Co2 retention drives equilibrium to the right
What happens when the reaction moves to the right?
increase in H+ concentration than HCO3- ions
small change in pH leads to a large change in the concentration of H+
When is Uncompensated respiratory acidosis is indicated?
pH < 7.35 and PCO2 > 45 mmHg
what is the compensation of respiratory acidosis?
nothing much as it is the buffer system that compensates and leads to this situation
What drives
increase in H+ ions from the renal tubular cells due as pushed forward by the pCO2
What happens to the bicarbonate ion concentration?
further increase it as a result of renal compensation
What is the correction for respiratory acidosis?
lowering pCO2 by restoration of the normal ventilation
What is respiratory alkalosis?
Excessive removal of CO2 by the body
causes of resp alkalosis
low inspired pO2 at high altitudes
hypercentilation
hysterical overbreathing
hypoxia stimulates the peripheral chemoreceptors –> increase ventilation
gets rid of too much carbon dioxide –> decreased pCO2
What happens in resp alokalosis to the ions?
drives the reaction towards the left hand side
decrease in H+ and HCO3-
lower than normal pCO2
When is Uncompensated respiratory alkalosis indicated
pH > 7.45 and PCO2 < 35 mmHg
What is the correction for respiratory alkalosis?
restoration of normal ventilatory
what is metabolic acidosis?
excess H+ from any other source other than CO2
What is the most common acid base dustrubance?
metabolic acidosis
causes of metabolic acidosis?
Ingestion of acids or acid-producing foodstuffs
Excessive metabolic production of H+
(e.g. lactic acid during exercise or ketoacidosis - DM)
Excessive loss of base from the body
(e.g. diarrhoea – loss of HCO3-, as they aren’t reabsorbed later on)
Uncompensated metabolic acidosis indicated by
pH < 7.35, [HCO3-]p is low
HCO3- is tyring to buffer the excess H+ (as the buffer system isnt involved in the process but it will eventually decrease the HCO3- concentration
What is the compensation for metabolic acidosis?
as a decrease in plasma pH
stimulates the peripheral chemoreceptors to increase ventilation and blow CO2 out
drives the buffer system towards the left hand side –> plasma H+ and HCO3 is reduced.
HCO3 further decreased - with ventilation and
What is the correction for metalbolic acidosis?
kidney is filtering less HCO3 than before
H+ secretion continues and produces TA and ammonium ==> to generate more HCO3
(helps to replenish the blood buffer stores)
urine –> acid secreted and HCO3 restored
additing of more hco3 to bring the plasma conc back to normal
What is the metabolci alkalosis?
Less common than metabolic acidosis
Excessive loss of H+ from the body
Causes of metabolic alkalosis?
Loss of HCl from the stomach (vomiting)
Ingestion of alkali or alkali-producing foods
(e.g. Ingestion of NaHCO3 as an antacid, though not a problem with modern antacids)
Aldosterone hypersecretion (causes stimulation of Na+/H+ exchange at the apical membrane of the tubule; acid secretion)
Uncompensated metabolic alkalosis indicated by:
pH > 7.45, [HCO3-]p is high
What is the compensation for metabolic alkalosis?
respiratory compensation
Increased pH slows ventilation (peripheral chemoreceptors)
CO2 retained, PCO2 rises
drives the qeaction forward, increase H+ secretion, increase the plasma concentration of HCO3 ions (rate of filtration of HCO3 increased as plasma concentration of hco3 increased)
can’t reabsorb all that hco3 hence excreted in the urine
no new TA or NH4+ added
by excreting HCO3 in the urine- –>
Correction ofr MA?
Filtered HCO3- load is so large compared to normal that not all of the filtered HCO3- is reabsorbed
No TA or NH4+ is generated
HCO3- is excreted (urine is alkaline)
[HCO3-]p falls back towards normal
