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SM Renal > Physiology 8 > Flashcards

Physiology 8 Flashcards

1
Q

What are the normal figures for a normal Acid-Base balance

A

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)

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2
Q

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

A

Restore pH asap through compensation

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3
Q

What is compensation of an AB disturbance

A

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

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4
Q

What is correction of an AB disturbance

A

restoration of pH and HCO3 and pCO2 to normal

I.e. all components back to normal

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5
Q

What are the two subdivisions of disturbances of respiratory origin

A 
respiratory acidosis (plasma pH falls)
Respiratory alkalosis (plasma pH rises)
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6
Q

What are the two subdivision of non-respiratory origin

A 
Metabolic acidosis (plasma pH falls)
Metabolic alkalosis (plasma pH rises
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7
Q

What is the most important buffer

A

CO2 buffer system

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8
Q

What is a blood buffer

A

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

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9
Q

How are buffers all present in the extracellular fluid

A

Due to the presence of bicarbonate ions

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10
Q

How quick is the response of the buffer stores

A

Very quick

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11
Q

What can measure the pH and pCO2 of the blood

A

A blood gas analyser

WE can then calculate the concentration of HCO3 ions

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12
Q

What is respiratory acidosis characterised by

A

retention of CO2 by the body

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13
Q

What are some causes of respiratory acidosis

A 
Chronic bronchitis 
Chronic emphysema 
airway restriction (bronchial asthma, tumour)
Chest injuries 
respiratory depression
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14
Q

What does a respiratory acidosis result in biochemically

A

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

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15
Q

When both the concentrations of H+ and Bicarb increase, why does it become acidotic

A

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

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16
Q

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

A

Less than normal pH i.e. 45mmHg because CO2 is retained in the body

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17
Q

Can a buffer buffer itself

A

no

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18
Q

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

A

caused by respiratory system

compensated by the renal system

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19
Q

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

A

The bicarb is the underlying issue due to CO2 retention

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20
Q

How does the renal system compensate for respiratory acidosis

A

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

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21
Q

What initially happens to the bicarb concentration in plasma

A

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
Q

What does the overall correction of the respiratory acidosis require

A

lowering pCO2 by restoring normal ventilation by restoring normal respiratory function

23
Q

What is a respiratory alkalosis

A

Excessive removal of CO2 by the body

24
Q

What are some examples of respiratory alkalosis

A

Low inspired pO2 at high altitude (hypoxia stimulates peripheral chemoreceptors, hyperventilation lowers pCO2)
Hyperventilation (causes include fever, brainstem damage)
Hysterical over breathing

25
Q

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

A

They both fall

26
Q

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

A

pH >7.45 and pCO2

27
Q

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

A

Partial pressure of CO2 (pCO2)

28
Q

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

A

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

29
Q

Renal compensation of respiratory alkalosis does what to the HCO3

A

Further lowers the HCO3 concentration

30
Q

What does correction of respiratory alkalosis require

A

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

31
Q

What is metabolic acidosis

A

Excess H+ from any source other than CO2

32
Q

What are some examples of metabolic acidosis

A

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
Q

Why is the bicarb concentration depleted in metabolic acidosis

A

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

34
Q

What are the biochemical indications of a metabolic acidosis

A

pH

35
Q

What does a decrease in plasma pH stimulate

A

peripheral chemoreceptors

36
Q

How might we lower the plasma concentration of H+ ions

A

quickly increasing Ventilation due to the stimulation of peripheral chemoreceptors

37
Q

How do we lower the plasma concentration of H+ ions

A

By stimulating ventilation, we blow off CO2 which then results in lowering H+ and HCO3-

38
Q

How do we get rid of some of the acid load

A

We add new bicarbonate ions

Lose H+ in TA and NH4

39
Q

Why is respiratory compensation essential for metabolic acidosis

A

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

40
Q

Why does the concentration of bicarbonate ions further decrease

A

As a result of increased ventilation

41
Q

What is metabolic alkalosis

A

Excess loss of H+ form the body

42
Q

How might metabolic alkalosis arise

A

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
Q

What is an uncompensated metabolic alkalosis

A

pH >7.45 and High Bicarbonate concentration

44
Q

What will the increase in pH lead to

A

CO2 retention

45
Q

What lowers the pH in metabolic alkalosis

A

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

46
Q

How are bicarbonate ions lowered in metabolic alkalosis

A

They are excreted in urine and are not reabsorbed

47
Q

What is the cause of a respiratory alkalosis or acidosis

A

Respiratory system

48
Q

What does correction of respiratory alkalosis or acidosis require

A

Restoration of normal respiratory system function

49
Q

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

A

the respiratory system is not the underlying cause

50
Q

If there is an increase pCO2, then what happens to the buffer

A

There is little extracellular buffering and therefore it is up to the renal system to compensate and correct

SM Renal (23 decks)

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