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BMS 242 - CVS respiratory > Acid base balance I > Flashcards

Acid base balance I Flashcards

1
Q

Why is acid/base balance so important?

A

Small changes in pH –> huge impacts on the body

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2
Q

How is pH calculated?

A

pH = -log10 [H+]

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3
Q

What is the normal pH range in the body?

A

7.35-7.45

BUT, there are SOME tissues which sit outside of this range

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4
Q

What is the pH scale described as?

What does this mean?

A

1) A log scale
- For every 1 unit change in pH, theres is a X10 change in [H+]

2) A reciprocal scale
- Increase in pH, decrease in [H+]

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5
Q

What does a pH of 7.35-7.45 correspond to in [H+]?

A

45-35 nmoles/litre

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6
Q

What happens to the pH in the capillary bed?

A

Drops from 7.45 to 7.35

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7
Q

What is pH above 7.45 classed as?

A

Alkalosis

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8
Q

What is pH below 7.35 classed as?

A

Acidosis

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9
Q

What 3 major things can fluctuations in [H+] have an effect on?

A

1) Excitability of muscles/nerves
2) Enzyme activities
3) K+ levels

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10
Q

How do changes in [H+] change the excitability of muscles/nerves?

A

Changes the binding of H+ to the ion channels associated with excitability

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11
Q

How do changes in [H+] change enzyme activities?

A

Enzymes are pH sensitive

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12
Q

How do changes in [H+] change K+ levels?

What does this cause?

A

Increase in [H+] concentration in the plasma decreases [K+] in the cell as:

  • Body tries to get rid of H+ in the plasma, by transporting it into the cell
  • As the expense of K+ - transported out

Causes:

  • Hyperkalemia
  • Impact on the excitable cells of the body
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13
Q

What is the pH of gastric secretions?

A

0.7

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14
Q

What is the pH of CSF?

A

7.3

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15
Q

What is the pH of pancreatic secretions?

A

8.1

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16
Q

What is the pH of the final urine?

A

5.4

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17
Q

What are the sources of acid/alkali?

A

1) Metabolism

2) Diet

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18
Q

What produces more H+, metabolism or diet?

A

Metabolism (double at 40mmol/day)

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19
Q

What is lost in the diet?

A

10 mmol/day of OH-

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20
Q

What produces a lot of alkali?

A

Fruit

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21
Q

Why is the western diet an excess of H+?

A

Protein rich - lots of H+

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22
Q

How much excess of H+ is there per day?

Why must happen to this H+?

A

Net excess of 70mmol/day

Must be regulated to prevent acidosis

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23
Q

What are the 3 systems that regulate acid levels in the body?

How long does it take for the 3 systems to act?

A

1) Blood and tissue BUFFERS
- Takes seconds

2) Respiration
- Takes minutes

3) Renal
- Takes hours/days

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24
Q

What do buffers do to regulate H+ levels?

A

Bind to free H+

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25
Q

How does respiration regulate H+ levels?

A

Rids of CO2

26
Q

How does the renal system regulate H+ levels?

A

By direct excretion

27
Q

Where are pH buffers present in the body? (4)

A
  • Blood (plasma and RBC)
  • ECF
  • ICF
  • Urine
28
Q

What are 4 examples of buffers in the body?

A

1) Heamoglobin
2) HCO3-
4) Inorganic phosphate
5) Weak acids/bases on PROTEINS

29
Q

What is the equilibrium system involving bicarbonate?

What happens if increase CO2?

What happens if increase H+?

A

CO2 + H20 H2CO3 H+ + HCO3-

Increase CO2:

1) Shift eq to the RIGHT
2) Extra CO2 bind with H2O and form H2CO3
3) H2CO3 dissociates into H+ + HCO3-
4) pH decreases

Increase H+:

1) Shift eq to the LEFT
2) H+ bind with HCO3 to form H2CO3
3) H2CO3 dissociates into H2O and CO2

30
Q

What is CO2?

A

An acidifier

31
Q

What is the Henderson-Hasselbalch equation?

A

pH = pK + log [HCO3]/[H2CO3]

Where:

  • pK is a constant
  • H2CO3 ~CO2
32
Q

What is the value for pK at 37 degrees C?

A

6.1

33
Q

What is the normal ratio of [HCO3]/[H2CO3]?

A

20:1

34
Q

At pH 7.4, what is the normal [HCO3]?

A

25mM

35
Q

What happens to pH and [HCO3-] when acid is added?

What is this common of?

A

Both low

Common of metabolic acidosis

36
Q

What happens to pH and [HCO3-] when base is added?

What is this common of?

A

Both high

Common of metabolic alkalosis

37
Q

What happens when decrease CO2?

What is this common of?

A

High pH and low [HCO3-]

Common of respiratory alkalosis

38
Q

What happens when increase CO2?

What is this common of?

A

Low pH and high [HCO3-]

Common of respiratory acidosis

39
Q

What is ‘metabolic acidosis/alkalosis’ to do with?

A

Addition or loss of acid/base from the body

40
Q

What is ‘respiratory acidosis/alkalosis’ to do with?

What does this highlight a problem with?

A

Level of CO2 in the body

Highlights a problem with the lungs

41
Q

What is the chemical control of ventilation?

How?

A

Peripheral and central chemoreceptors

Regulate the blood gas composition: PO2, PCO2, pH

42
Q

What 3 things triggers chemoreceptors?

A

1) Hypoxia (low O2)
2) Hypercapnia (high CO2)
3) Acidosis

43
Q

What happens when the chemoreceptors are activated?

What does this lead to?

A

Increase in VENTILATION

Leads to:

  • Increase in O2
  • Decrease in CO2
  • Increase in pH
44
Q

Where are peripheral chemoreceptors found?

A

In the carotid and aortic bodies

45
Q

What do the peripheral chemoreceptors regulate?

A

Plasma

46
Q

What is the MAIN stimulus for the peripheral chemoreceptors?

What does it cause them to do?

A

Hypoxia (low PO2)

Causes them to increase firing rate

47
Q

When the peripheral chemoreceptors are activated, where do they send signals through?

To where?

A

Through:

  • Sinus nerve
  • Glosso-pharyngeal nerve
  • Vagus nerve

To:

  • Medulla and respiratory centres
  • Which feed into the respiratory system to change breathing
48
Q

What is the main cell type in the peripheral chemoreceptor?

A

Glomus cell

49
Q

What is the structure of the carotid body?

A

Contains:

  • Glomus cells
  • Type II supporting cells
  • Sinusoids
  • Parasympthetic and sympathetic chemoreceptors
50
Q

Describe glomus cells?

A

Neural phenotype - fire action potentials when O2 drops

Release NEUROTRANSMITTERS - activate the cranial nerve afferents to the respiratory centres

51
Q

What are sinosoids?

A

Enlargement of blood vessel

52
Q

What do the PS and S ganglion cells do in the carotid body?

A
  • INPUT into the chemoreceptors
  • Regulate blood flow
  • Fine-tune activation
53
Q

How are aortic peripheral chemoreceptors different to carotid body peripheral chemoreceptors?

A

Small

Less well studied

54
Q

Describe the action potential firing in the glomus cell

A

1) Inhibition of BK K+ channels by increase PCO2, decrease O2 or decrease pH
2) Depolarisaion
3) Action potential firing
4) Voltage gated Ca2+ open - increase intracellular Ca2+
5) Fusion of vesicles containing neuroT - neuroT release
6) Afferent fibre stimulation
7) Signals to the rep centre

55
Q

What at the neurotransmitters released by the glomus cells onto the cranial afferents?

A
  • Ach
  • Dopamine
  • NA
  • 5-HT
  • Substance P
  • ANP
56
Q

How are hypoxia, hypercaptina and pH linked?

A

1) Sensitivity to PO2 changes with acid/base status

2) Sensitivity to PCO2 changes with pH

57
Q

What happens to sensitivity of the peripheral chemoreceptor to PO2 if pH decrease/CO2 increase?

A

Increases

58
Q

What happens to sensitivity of the peripheral chemoreceptor to PO2 if pH increase/CO2 decrease?

A

Decrease

59
Q

What happens to sensitivity of the peripheral chemoreceptor to PCO2 if pH increase increase?

A

Decrease

60
Q

What happens to sensitivity of the peripheral chemoreceptor to PCO2 if pH increase decrease?

A

Increase

BMS 242 - CVS respiratory (15 decks)

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