Physiology 8 Flashcards
What are the normal figures for a normal Acid-Base balance
Plasma pH close to 7.4 (7.35-7.45)
HCO3- close to 25 mmol/L (23-37(
Arterial pCO2 close to 40mmHg (35-45)
What is the main aim if we have a disruption of the normal acid-base
Restore pH asap through compensation
What is compensation of an AB disturbance
the restoration of pH irrespective of what happens to HCO3 and pCO2
What is correction of an AB disturbance
restoration of pH and HCO3 and pCO2 to normal
I.e. all components back to normal
What are the two subdivisions of disturbances of respiratory origin
respiratory acidosis (plasma pH falls) Respiratory alkalosis (plasma pH rises)
What are the two subdivision of non-respiratory origin
Metabolic acidosis (plasma pH falls) Metabolic alkalosis (plasma pH rises
What is the most important buffer
CO2 buffer system
What is a blood buffer
Haemoglobin - oxygenated blood has a greater affinity for ions compared to deoxygenated blood
How are buffers all present in the extracellular fluid
Due to the presence of bicarbonate ions
How quick is the response of the buffer stores
Very quick
What can measure the pH and pCO2 of the blood
A blood gas analyser
WE can then calculate the concentration of HCO3 ions
What is respiratory acidosis characterised by
retention of CO2 by the body
What are some causes of respiratory acidosis
Chronic bronchitis Chronic emphysema airway restriction (bronchial asthma, tumour) Chest injuries respiratory depression
What does a respiratory acidosis result in biochemically
An increase in both the plasma concentrations of both H+ and Bicarb
When both the concentrations of H+ and Bicarb increase, why does it become acidotic
There are many many more H+ ions than bicarb ions (nano rather than milli)
small changes in pH reflect higher changes in the H ion concentrations
If a patient has an uncompensated respiratory acidosis, what will the pH and the pCO2 be
Less than normal pH i.e. 45mmHg because CO2 is retained in the body
Can a buffer buffer itself
no
What is the cause of the respiratory acidosis and what compensates for it
caused by respiratory system
compensated by the renal system
Why can bicarb ions not mop up the excess H+ ions in respiratory acidosis
The bicarb is the underlying issue due to CO2 retention
How does the renal system compensate for respiratory acidosis
H+ secretion is stimulated
All filtered HCO3 is reabsorbed
H+ continues to be secretes and generates titratable acid (combine with phosphate ions) and NH4+
Acid is excreted and “new HCO3-“ is added to the blood
What initially happens to the bicarb concentration in plasma
Rises due to:
a) as a result of the disorder and
b) as a result of the renal compensation (due to excreting acid from the body)
What does the overall correction of the respiratory acidosis require
lowering pCO2 by restoring normal ventilation by restoring normal respiratory function
What is a respiratory alkalosis
Excessive removal of CO2 by the body
What are some examples of respiratory alkalosis
Low inspired pO2 at high altitude (hypoxia stimulates peripheral chemoreceptors, hyperventilation lowers pCO2)
Hyperventilation (causes include fever, brainstem damage)
Hysterical over breathing
What happens into the concentrations of bicarb and H+ in respiratory alkalosis
They both fall
If a patient has an uncompensated respiratory alkalosis, what will the pH and the pCO2 be
pH >7.45 and pCO2
What causes H+ secretion by the kidney (renal tubular cells)
Partial pressure of CO2 (pCO2)
If we reduce the pCO2 what happens to the H+ secretion
it is reduced (it is not enough to absorb the excess bicarb ions)
Renal compensation of respiratory alkalosis does what to the HCO3
Further lowers the HCO3 concentration
What does correction of respiratory alkalosis require
restoration of normal ventilation i.e. come down from high altitude or give oxygen
What is metabolic acidosis
Excess H+ from any source other than CO2
What are some examples of metabolic acidosis
Ingestion of acids or acid-producing foodstuffs
Excessive metabolic production of H+ (e.g. lactic acid during exercise or ketoacidosis)
excessive loss of base from the body (e.g. severe diarrhoea - loss of HCO3 which are normally reabsorbed back into the blood)
Why is the bicarb concentration depleted in metabolic acidosis
As a result of buffering excess H+ or loss of HCO3- from the body
What are the biochemical indications of a metabolic acidosis
pH
What does a decrease in plasma pH stimulate
peripheral chemoreceptors
How might we lower the plasma concentration of H+ ions
quickly increasing Ventilation due to the stimulation of peripheral chemoreceptors
How do we lower the plasma concentration of H+ ions
By stimulating ventilation, we blow off CO2 which then results in lowering H+ and HCO3-
How do we get rid of some of the acid load
We add new bicarbonate ions
Lose H+ in TA and NH4
Why is respiratory compensation essential for metabolic acidosis
Acid load cannot be excreted immediately and therefore respiratory compensation is essential
Why does the concentration of bicarbonate ions further decrease
As a result of increased ventilation
What is metabolic alkalosis
Excess loss of H+ form the body
How might metabolic alkalosis arise
Excessive vomiting
Ingestion of alkali or alkali-producing foods
Aldosterone hypersecretion (stimulation of Na/H exchange at the apical membrane of the tubule; acid secretion)
What is an uncompensated metabolic alkalosis
pH >7.45 and High Bicarbonate concentration
What will the increase in pH lead to
CO2 retention
What lowers the pH in metabolic alkalosis
H+ ions rise (which also causes an increase of HCO3-)
How are bicarbonate ions lowered in metabolic alkalosis
They are excreted in urine and are not reabsorbed
What is the cause of a respiratory alkalosis or acidosis
Respiratory system
What does correction of respiratory alkalosis or acidosis require
Restoration of normal respiratory system function
Why can the respiratory system contribute for a metabolic acidosis/ alkalosis
the respiratory system is not the underlying cause
If there is an increase pCO2, then what happens to the buffer
There is little extracellular buffering and therefore it is up to the renal system to compensate and correct
