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Flashcards in Physiology 8 Deck (50):
1

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)

2

What is the main aim if we have a disruption of the normal acid-base

Restore pH asap through compensation

3

What is compensation of an AB disturbance

the restoration of pH irrespective of what happens to HCO3 and pCO2

4

What is correction of an AB disturbance

restoration of pH and HCO3 and pCO2 to normal
I.e. all components back to normal

5

What are the two subdivisions of disturbances of respiratory origin

respiratory acidosis (plasma pH falls)
Respiratory alkalosis (plasma pH rises)

6

What are the two subdivision of non-respiratory origin

Metabolic acidosis (plasma pH falls)
Metabolic alkalosis (plasma pH rises

7

What is the most important buffer

CO2 buffer system

8

What is a blood buffer

Haemoglobin - oxygenated blood has a greater affinity for ions compared to deoxygenated blood

9

How are buffers all present in the extracellular fluid

Due to the presence of bicarbonate ions

10

How quick is the response of the buffer stores

Very quick

11

What can measure the pH and pCO2 of the blood

A blood gas analyser
WE can then calculate the concentration of HCO3 ions

12

What is respiratory acidosis characterised by

retention of CO2 by the body

13

What are some causes of respiratory acidosis

Chronic bronchitis
Chronic emphysema
airway restriction (bronchial asthma, tumour)
Chest injuries
respiratory depression

14

What does a respiratory acidosis result in biochemically

An increase in both the plasma concentrations of both H+ and Bicarb

15

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

16

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

17

Can a buffer buffer itself

no

18

What is the cause of the respiratory acidosis and what compensates for it

caused by respiratory system
compensated by the renal system

19

Why can bicarb ions not mop up the excess H+ ions in respiratory acidosis

The bicarb is the underlying issue due to CO2 retention

20

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

21

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)

22

What does the overall correction of the respiratory acidosis require

lowering pCO2 by restoring normal ventilation by restoring normal respiratory function

23

What is a respiratory alkalosis

Excessive removal of CO2 by the body

24

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

25

What happens into the concentrations of bicarb and H+ in respiratory alkalosis

They both fall

26

If a patient has an uncompensated respiratory alkalosis, what will the pH and the pCO2 be

pH >7.45 and pCO2

27

What causes H+ secretion by the kidney (renal tubular cells)

Partial pressure of CO2 (pCO2)

28

If we reduce the pCO2 what happens to the H+ secretion

it is reduced (it is not enough to absorb the excess bicarb ions)

29

Renal compensation of respiratory alkalosis does what to the HCO3

Further lowers the HCO3 concentration

30

What does correction of respiratory alkalosis require

restoration of normal ventilation i.e. come down from high altitude or give oxygen

31

What is metabolic acidosis

Excess H+ from any source other than CO2

32

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)

33

Why is the bicarb concentration depleted in metabolic acidosis

As a result of buffering excess H+ or loss of HCO3- from the body

34

What are the biochemical indications of a metabolic acidosis

pH

35

What does a decrease in plasma pH stimulate

peripheral chemoreceptors

36

How might we lower the plasma concentration of H+ ions

quickly increasing Ventilation due to the stimulation of peripheral chemoreceptors

37

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-

38

How do we get rid of some of the acid load

We add new bicarbonate ions
Lose H+ in TA and NH4

39

Why is respiratory compensation essential for metabolic acidosis

Acid load cannot be excreted immediately and therefore respiratory compensation is essential

40

Why does the concentration of bicarbonate ions further decrease

As a result of increased ventilation

41

What is metabolic alkalosis

Excess loss of H+ form the body

42

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)

43

What is an uncompensated metabolic alkalosis

pH >7.45 and High Bicarbonate concentration

44

What will the increase in pH lead to

CO2 retention

45

What lowers the pH in metabolic alkalosis

H+ ions rise (which also causes an increase of HCO3-)

46

How are bicarbonate ions lowered in metabolic alkalosis

They are excreted in urine and are not reabsorbed

47

What is the cause of a respiratory alkalosis or acidosis

Respiratory system

48

What does correction of respiratory alkalosis or acidosis require

Restoration of normal respiratory system function

49

Why can the respiratory system contribute for a metabolic acidosis/ alkalosis

the respiratory system is not the underlying cause

50

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