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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
What does the buffering of H+ by the haemoglobin depend on?
Level of oxygenation
26
What happens to the amount of H+ ions that can bind to Hb as more O2 binds to Hb?
The haemoglobin switches into the R state | -Less H+ ions bind as a result
27
What happens to the amount of H+ ions that can bind to Hb as less O2 binds to Hb?
The haemoglobin switches to the T state | -More H+ ions bind
28
How does the amount of CO2 increase in plasma in the venous system? How does this affect the pH?
- 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
What happens when venous blood arrives at the lungs?
- 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
How are carbamino compounds formed?
- 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
Why are more carbamino compounds formed at the tissues?
-The pCO2 is higher and unloading of oxygen facilitates binding of CO2 to haemoglobin
32
What are the forms that CO2 is transported in?
- Dissolved CO2 - Hydrogen carbonate - Carbamino compounds
33
What is the main role of CO2 in blood?
-Acts as part of the pH buffering system Only 8% of the total CO2 is transported
34
What is hypercapnia?
Rise in pCO2
35
What is hypocapnia?
Fall in pCO2
36
What is hypoxia?
Fall in pO2
37
How does exercise affect the partial pressure of CO2 and O2?
- pO2 drops and pCO2 rises | - Breathing more will restore both
38
What is hyperventilation?
Ventilation increase without change in metabolsim
39
What is hypoventilation?
Ventilation increase without change in metabolism
40
What happens to pCO2 and pO2 in hyperventilation?
- pO2 will rise | - pCO2 will fall
41
What happens to pCO2 and pO2 in hypoventilation?
- pO2 will fall | - pCO2 will rise
42
What happens if the pO2 changes without a change in CO2?
Correction of the pO2 will cause the pCO2 to drop | This leads to hypocapnia
43
Control system are in place to prevent marked hypoxia. True/False
True
44
What is the effect of CO2 on plasma pH if bicarbonate remains unchanged?
- If pCO2 increase then pH falls - If pCO2 decreases then pH rises Small changes in pCO2 lead to large changes in pH.
45
What are the effects of pH falling and pH rising?
- If pH falls below 7.0 then enzymes become denatured | - If pH rises above 7.6 free calcium concentration drops leading to tetany
46
What are the effects of hypercapnia on plasma pH?
-Respiratory acidosis due to fall in plasma pH
47
What are the effects of hypocapnia on plasma pH?
-Respiratory alkalosis due to rise in plasma pH
48
How does the kidney compensate for respiratory acidosis?
- Kidneys increase reabsorption of HCO3- - This compensate for the the increase in HCO3- (can take 2-3 days)
49
How does the kidney compensate for respiratory alkalosis?
- Kidneys decrease reabsorption of HCO3- - This compensates for the decrease in HCO3- (can take 2-3 days)
50
How does metabolic acidosis occur?
- If tissues produce acid, this reacts with HCO3- - Fall in [HCO3-] leads to fall in pH - This causes metabolic acidosis
51
How is metabolic acidosis compensated for?
- Compensated for by changing ventilation - Increased ventilation lowers pCO2 - Restores pH towards normal
52
How does metabolic alkalosis occur?
- If the plasma HCO3- rises - Plasma pH rises - Causes metabolic alkalosis
53
How is metabolic alkalosis compensated for?
-Decreasing ventilation so that pO2 falls and pCO2 increases
54
How are the respiratory pathways controlled?
- Sensores located in CNS and the periphery feed information back to the control centre for processing - Ventilation is adjusted as necessary
55
What are the examples of peripheral chemoreceptors?
-Carotid and aortic bodies
56
What stimulates the peripheral chemoreceptors and what does it lead to?
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
What is the sensitivity of the peripheral chemoreceptors to the pCO2?
Relatively insensitive to pCO2
58
What is the sensitivity of the central chemoreceptors to the pCO2?
Sensitive to the pCO2
59
Where are the central chemoreceptors found?
Medulla of the brain
60
Why isn't the central chemoreceptor affected by bicarbonate ions and H+ but it is affected by CO2?
- 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
How do the central chemoreceptors work?
- 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
How is CSF pH determined?
- 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
How do the central chemoreceptors counteract an increase in the pCO2?
- 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
What is the action of the choroid plexus?
- 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
How does persisting hypoxia affect the central chemoreceptors?
- 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
How does persisting hypoxia and hypocapnia affect the central chemoreceptors?
- 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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