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Flashcards in Physiology 8 Deck (50)
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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



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