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Semester 3: Respiratory > Session 4 > Flashcards

Session 4 Flashcards

1
Q

What are the features of carbon dioxide when compared with posterior

A

It is more soluble
It reacts chemically with water
React with haemoglobin as well
2.5 times as much in arterial blood

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2
Q

CO2 control is more important for pH than for transporting it from the tissues to the lungs. True/False

A

True

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3
Q

What is the pH range that arterial blood must be kept in?

A

7.35-7.45

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4
Q

How does CO2 interact with arterial blood?

A

Reacts with water in plasma and red blood cells. It is not there as a waste product

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5
Q

What does dissolved CO2 form in blood?

A

Reacts with water to form carbonic acid

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6
Q

Why is does the amount of carbonic acid need to be controlled>

A

Dissociates quickly to hydrogen ions and hydrogen carbonate ions.

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7
Q

The reaction that form carbonic acid from CO2 and water is irreversible. True/False

A

False. It reversible and rate of reaction depends on reactants and products

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8
Q

What does the pH of plasma depend on?

A

-Depends on how much CO2 reacts to form H+ (dissolved CO2 pushes the reaction to the right and HCO3- pushes the reaction to the left)
This depends on dissolved CO2 and concentration of hydrogen carbonate

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9
Q

What determines how much CO2 dissolved in the plasma?

A

-Partial pressure of CO2

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10
Q

What happens to plasma pH when pCO2 rises?

A

Becomes more acidic

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11
Q

What happens to the plasma pH when the pCO2 falls?

A

It will become more alkaline

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12
Q

What is the determining factors for dissolved CO2?

A

pCO2 of alveoli which is controlled by rate of breathing

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13
Q

What does high HCO3- prevent from happening in the blood?

A

Prevent nearly all dissolved CO2 from reacting

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14
Q

What determines the pH of arterial blood?

A

Ratio of HCO3- and pCO2.

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15
Q

What is the Henderson-Hasselbalch equation?

A

pH=pK+log([HCO3-])/(pCO2 X 0.23))

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16
Q

What enzyme speeds up the reaction that speeds up hydrogen carbonate production in red blood cells?

A

Carbonic anhydrase

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17
Q

How do the red blood cells produce hydrogen carbonate?

A
  • H+ ions bind to the negatively charged Hb inside the red blood cells
  • Chloride-bicarbonate exchanger transports HCO3- out of red blood cells which is left front he reaction between CO2 and H2O.
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18
Q

Eythrocytes control concentration of HCO3- in plasma. True/False

A

False. They merely produce HCO3-.

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19
Q

What determine the amount of HCO3- that is produced by the erythrocytes?

A

Binding of H+ to haemoglobin

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20
Q

What is the main determant of plasma hydrogen carbonate? pCO2 or erythrocytes ?

A

Most of the HCO3- comes from the red blood cells

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21
Q

What is the role of the kidney in controlling HCO3-?

A

The kidney controls the amount of HCO3- by varying the excretion of bicarbonate.

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22
Q

How does hydrogen carbonate buffer extra acid?

A

Acids react with HCO3- to produce CO2. Therefore the bicarbonate decreases.
CO2 produced is removed by breathing and pH changes are minimised

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23
Q

What determine arterial pCO2?

A

Alveolar pCO2 which determine how much CO2 is dissolved. This therefore affects pH.

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24
Q

pCO2 is higher in venous blood than arterial blood. True/false

A

True. It is returning from metabolically active tissue so more CO2 is dissolved

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25
Q

What does the buffering of H+ by the haemoglobin depend on?

A

Level of oxygenation

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26
Q

What happens to the amount of H+ ions that can bind to Hb as more O2 binds to Hb?

A

The haemoglobin switches into the R state

-Less H+ ions bind as a result

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27
Q

What happens to the amount of H+ ions that can bind to Hb as less O2 binds to Hb?

A

The haemoglobin switches to the T state

-More H+ ions bind

28
Q

How does the amount of CO2 increase in plasma in the venous system?

How does this affect the pH?

A
  • Less O2 bound to Hb so haemoglobin switches to the T state
  • More H+ ions bind to Hb
  • More HCO3- can be produced and is exported to the plasma
  • Therefore more CO2 is present in plasma in venous system.

-More HCO3- is also present so therefore ratio is similar. Small change in plasma pH as both CO2 and HCO3- have increased

29
Q

What happens when venous blood arrives at the lungs?

A
  • Hb picks up O2 and goes into R-state
  • Causes Hb to give up the extra H+ it took on at the tissues
  • H+ reacts with HCO3- to form CO2
  • CO2 is breathed out
30
Q

How are carbamino compounds formed?

A
  • CO2 binds directly to amine groups on the globulin on Hb.
  • This contribute to the CO2 transport but it is not part of the acid base balance
  • This is CO2 given up at the lungs
31
Q

Why are more carbamino compounds formed at the tissues?

A

-The pCO2 is higher and unloading of oxygen facilitates binding of CO2 to haemoglobin

32
Q

What are the forms that CO2 is transported in?

A
  • Dissolved CO2
  • Hydrogen carbonate
  • Carbamino compounds
33
Q

What is the main role of CO2 in blood?

A

-Acts as part of the pH buffering system

Only 8% of the total CO2 is transported

34
Q

What is hypercapnia?

A

Rise in pCO2

35
Q

What is hypocapnia?

A

Fall in pCO2

36
Q

What is hypoxia?

A

Fall in pO2

37
Q

How does exercise affect the partial pressure of CO2 and O2?

A
  • pO2 drops and pCO2 rises

- Breathing more will restore both

38
Q

What is hyperventilation?

A

Ventilation increase without change in metabolsim

39
Q

What is hypoventilation?

A

Ventilation increase without change in metabolism

40
Q

What happens to pCO2 and pO2 in hyperventilation?

A
  • pO2 will rise

- pCO2 will fall

41
Q

What happens to pCO2 and pO2 in hypoventilation?

A
  • pO2 will fall

- pCO2 will rise

42
Q

What happens if the pO2 changes without a change in CO2?

A

Correction of the pO2 will cause the pCO2 to drop

This leads to hypocapnia

43
Q

Control system are in place to prevent marked hypoxia. True/False

A

True

44
Q

What is the effect of CO2 on plasma pH if bicarbonate remains unchanged?

A
  • If pCO2 increase then pH falls
  • If pCO2 decreases then pH rises

Small changes in pCO2 lead to large changes in pH.

45
Q

What are the effects of pH falling and pH rising?

A
  • If pH falls below 7.0 then enzymes become denatured

- If pH rises above 7.6 free calcium concentration drops leading to tetany

46
Q

What are the effects of hypercapnia on plasma pH?

A

-Respiratory acidosis due to fall in plasma pH

47
Q

What are the effects of hypocapnia on plasma pH?

A

-Respiratory alkalosis due to rise in plasma pH

48
Q

How does the kidney compensate for respiratory acidosis?

A
  • Kidneys increase reabsorption of HCO3-
  • This compensate for the the increase in HCO3-

(can take 2-3 days)

49
Q

How does the kidney compensate for respiratory alkalosis?

A
  • Kidneys decrease reabsorption of HCO3-
  • This compensates for the decrease in HCO3-

(can take 2-3 days)

50
Q

How does metabolic acidosis occur?

A
  • If tissues produce acid, this reacts with HCO3-
  • Fall in [HCO3-] leads to fall in pH
  • This causes metabolic acidosis
51
Q

How is metabolic acidosis compensated for?

A
  • Compensated for by changing ventilation
  • Increased ventilation lowers pCO2
  • Restores pH towards normal
52
Q

How does metabolic alkalosis occur?

A
  • If the plasma HCO3- rises
  • Plasma pH rises
  • Causes metabolic alkalosis
53
Q

How is metabolic alkalosis compensated for?

A

-Decreasing ventilation so that pO2 falls and pCO2 increases

54
Q

How are the respiratory pathways controlled?

A
  • Sensores located in CNS and the periphery feed information back to the control centre for processing
  • Ventilation is adjusted as necessary
55
Q

What are the examples of peripheral chemoreceptors?

A

-Carotid and aortic bodies

56
Q

What stimulates the peripheral chemoreceptors and what does it lead to?

A

Large falls in pO2 stimulate the peripheral chemoreceptors. This leads to

  • Increased breathing
  • Changes in the heart rate
  • Changes in blood flow distribution which increases the glow to the brain and kidneys
57
Q

What is the sensitivity of the peripheral chemoreceptors to the pCO2?

A

Relatively insensitive to pCO2

58
Q

What is the sensitivity of the central chemoreceptors to the pCO2?

A

Sensitive to the pCO2

59
Q

Where are the central chemoreceptors found?

A

Medulla of the brain

60
Q

Why isn’t the central chemoreceptor affected by bicarbonate ions and H+ but it is affected by CO2?

A
  • The ECF and CSF is impermeable to HCO3- and H+ due to the blood brain barrier
  • The blood brain barrier is selective permeable to CO2 however
61
Q

How do the central chemoreceptors work?

A
  • Respond to changes in the pH of cerebrospinal-spinal fluid
  • CSF is operated from blood by the blood brain barrier
  • CSF [HCO3-] is controlled by choroid plexus cells
  • CSF pCO2 is determined by arterial pCO2
62
Q

How is CSF pH determined?

A
  • Determined by ratio of [HCO3-]
  • [HCO3-] fixed in the short term as the blood brain brairer is impermeable to HCO3-
  • Falls in pCO2 lead to rise in CSF pH
  • Rises in pCO2 lead to falls in CSF pH
  • Persisting changes in pH corrected by choroid plexus cells which change the [HCO3-]
63
Q

How do the central chemoreceptors counteract an increase in the pCO2?

A
  • Elevated pCO2 drives the CO2 into the CSF across the blood brain barrier
  • CSF [HCO3-] is initially constant
  • CSF pH falls
  • Fall in CSF pH detected by central chemoreceptors
  • Drives increased ventilation
  • This lowers the pCO2 to restore the CSF pH
64
Q

What is the action of the choroid plexus?

A
  • Determine what is normal
  • CSF [HCO3-] determine which pCO2 is associated with normal CSF pH.
  • CSF [HCO3-] therefore sets the control system to a particular pCO2
  • Can be reset by changing CSF [HCO3-] with persistent hypercapnia
65
Q

How does persisting hypoxia affect the central chemoreceptors?

A
  • Hypoxia is detected by the peripheral chemoreceptors which will trigger increase in ventilation
  • pCO2 will fall further and this causes decrease in ventilation
  • CSF composition compensates for the altered pCO2
  • Choroid plexus cells selectively add H+ or HCO3- into the CSF
  • Central chemoreceptors accept the pCO2 as normal
66
Q

How does persisting hypoxia and hypocapnia affect the central chemoreceptors?

A
  • Hypoxia and hypercapnia
  • Respiratory acidosis
  • Decreased pH of CSF
  • Peripheral and central chemoreceptors stimulate breathing
  • Acidic pH undesirable for neurone
  • Therefore choroid plexus needs to adjust the pH of CSF
  • Addition of HCO3-
  • Central chemoreceptors accepted the high pCO2 as normal

Semester 3: Respiratory (4 decks)

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