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Respiratory System > Carbon Dioxide In Blood And Chemical Control Of Breathing > Flashcards

Carbon Dioxide In Blood And Chemical Control Of Breathing Flashcards

1
Q

How much more carbon dioxide is there in arterial blood than oxygen?

A

2.5 x

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2
Q

What is the total content of carbon dioxide in arterial blood?

A

21 mmol/L

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3
Q

What is the total content of oxygen in arterial blood?

A

8.9 mmol/L

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4
Q

What range must we keep arterial blood pH between?

A

7.35 - 7.45

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5
Q

How do we work out the concentration of carbon dioxide dissolved?

A

Solubility of CO2 x partial pressure CO2

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6
Q

What is the solubility factor of carbon dioxide at 37’C?

A

0.23 mmol/L/kPa

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7
Q

How does carbon dioxide reaction with water?

A

CO2 and water reacts to form carbonic acid (H2CO3)
Very quickly dissociates to form H+ and HCO3-
Reversible reaction

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8
Q

What does the pH of the blood depend on?

A

CO2 dissolved that reacts to form H+

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9
Q

What is the partial pressure of CO2 in the alveoli determined by?

A

Rate of breathing

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10
Q

What happens to the partial pressure of CO2 if we hyperventilate?

A

Decreases

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11
Q

What happens to the partial pressure of CO2 if we hypoventilate?

A

PCO2 increases

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12
Q

What is the normal concentration of HCO3- in the plasma?

A

25 mmol/L

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13
Q

What is the cation mostly associated with HCO3-?

A

Na+

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14
Q

How does a high HCO3- affect CO2?

A

Pushes the equation to the left
Prevents nearly all of the CO2 from reaction
Therefore plasma is alkaline

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15
Q

What is the equation for calculating pH from pCO2 and HCO3-?

A

Henderson-Hasselbach Equation

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

pK = constant 6.1 at body temperature

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16
Q

What is the normal ratio of HCO3- to CO2?

A

20:1

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17
Q

Which enzyme speeds up the reaction of CO2 and water?

A 
Carbonic anhydrase (CA)
In RBCs
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18
Q

What happens to the products of the CO2 reaction in a RBC?

A

H+ ions bind to negatively charged Hb

Chloride bicarbonate exchanger (antiporter) transports HCO3- out of RBCs

19
Q

Where is the concentration of HCO3- in the body controlled?

A

Kidneys

20
Q

What happens when the body produces acids?

A

React with HCO3- to produce CO2

Removed via breathing

21
Q

What happens when venous blood arrives at the lungs?

A

Hb picks up oxygen - goes into R state
Hb gives up the extra H+ it took on in the tissues
H+ reacts with HCO3- to form CO2 which is breathed out

22
Q

Describe the formation of carbamino compounds

A

Carbon dioxide binds directly to proteins
Carbon dioxide binds directly to amine groups on globin of Hb
More carbamino compounds formed at the tissues because partial pressure of carbon dioxide higher

23
Q

Name the 3 forms in which carbon dioxide is transported

A

Dissolved carbon dioxide (10%)
As hydrogen carbonate (60%)
As carbamino compounds (30%)

24
Q

What is the concentration of carbon dioxide in the venous blood?

A

23 mmol/L

25
Q

What is the partial pressure range for CO2 in the blood?

A

4.2 - 6.0 kPa

26
Q

What is the partial pressure range for oxygen in the blood?

A

9.8 - 14.2 kPa

27
Q

What is the reference range for concentration of HCO3- in the blood?

A

21-29 mmol/L

28
Q

Why can the partial pressure of oxygen drop considerably before saturation is markedly affected?

A

Plateau at the top of the oxygen-Hb saturation curve

Cooperative binding of Hb

29
Q

How long does the compensation of acidosis or alkalosis take in the kidneys?

A

Correction to the needed level of HCO3- takes 2-3 days

30
Q

How is metabolic acidosis compensated by changing ventilation?

A

Increased ventilation
Decreases partial pressure of carbon dioxide
Increases the pH

31
Q

What do central chemoreceptors detect?

A

H+

32
Q

What do peripheral chemoreceptors detect?

A

Oxygen
Carbon dioxide
H+

33
Q

Where are peripheral chemoreceptors located?

A

Carotid and aortic bodies

34
Q

What do large falls in pO2 stimulate?

A

Increased breathing
Changes in HR
Changes in blood flow distribution

35
Q

What are peripheral chemoreceptors typically insensitive to?

A

pCO2

36
Q

Where are the central chemoreceptors located?

A

Medulla of brain

37
Q

What are the central chemoreceptors detecting?

A

The partial pressure of carbon dioxide

Changes in pH of the CSF

38
Q

What controls the concentration of HCO3- in the CSF?

A

Choroid plexus cells

39
Q

What is the pCO2 in the CSF determined by?

A

Arterial pCO2

40
Q

Why does the pH change in the CSF in response to change in pCO2?

A

HCO3- cannot compensate for the change in pCO2 because the BBB is impermeable to HCO3-
(Persisting changes in pH will be corrected by the choroid plexus cells but takes a long time)

41
Q

What happens when there is an elevated pCO2?

A 
pH decreases 
Detected by the central chemoreceptors 
Increased ventilation 
Decreased pCO2
Restore CSF pH
42
Q

What happens in persisting hypoxia?

A

Detected by peripheral chemoreceptors
Increased ventilation
(This decreases CO2 which can be bad if a type 2 resp failure)

43
Q

What happens during persisting hypercapnia?

A

Respiratory acidosis
Decreased pH of CSF
Peripheral and central chemoreceptors increase ventilation

Respiratory System (13 decks)

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