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Flashcards in Physiology Deck (252):
1

what is the internal respiration equation?

food + oxygen = energy + carbon dioxide (+ water)
consumption of oxygen and production of carbon dioxide

2

what does external respiration refer to?

the exchange of oxygen and carbon dioxide between external environment and the cells of the body

3

how many steps are involved in external respiration?

4

4

what is the 1st step of external respiration?

ventilation

5

what is the 2nd step of external respiration?

gas exchange between alveoli and blood

6

what is the 3rd step of external respiration?

gas transport in the blood

7

what is the 4th step of external respiration?

gas exchange at tissue level

8

what does ventilation (1st step of external respiration) involve?

the mechanical process of gas exchange between the armosphere and the alveoli

9

what does 'gas exchange between alveoli and blood' (2nd step of external respiration) involve?

exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries

10

what does 'gas transport in the blood' (3rd step of external respiration) involve?

the binding and transport of oxygen and carbon dioxide in the circulating blood

11

what does 'gas exchange at tissue level' (4th step of external respiration) involve?

the exchange of oxygen and carbon dioxide between the blood in the systemic circulation and the body cells

12

what 3 body systems are involved in external respiration?

respiratory system
cardiovascular system
haematology system

13

What is Boyle's Law?

for a given mass of gas -at a certain temperature- as the volume of the gas increases, the pressure exerted by the gas decreases.

14

air flows down a pressure gradient ___ pressure to a region of ___ pressure

high pressure to a region of low pressure

15

when is the intra-alveolar pressure equivalent to the atmospheric pressure?

before inspiration

16

What does expansion of the thorax and lungs do to the intra-alveolar pressure?

makes it fall below atmospheric pressure (Boyle's Law)
this allows air to move from atmosphere into lungs down pressure gradient

17

what 2 forces hold the thoracic wall and the lungs in close opposition?

1. intrapleural fluid cohesiveness
2. the negative intrapleural pressure

18

how does the intrapleural fluid keep thoracic wall and lungs in close opposition?

the water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart, therefore pleural membranes tend to stick together

19

how does the negative intrapleural pressure keep the thoracic wall and lungs in close opposition?

the sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and chest wall, therefore lungs are forced to expand outwards while the chest is forced to squeeze inwards

20

what 3 pressures are important in ventilation?

atmospheric pressure
intra-alveolar pressure
intrapleural pressure

21

what is the atmospheric pressure at sea level?

760mmHg

22

what is usually the intrapleural pressure?

756mmHg

23

when the external intercostal muscle contract what do they cause?

elevation of the ribs, causing the sternum to move upwards and forwards- increases AP dimension of thoracic cavity

24

what type of process is inspiration?

active
(brought about by contraction of inspiratory muscles)

25

what type of process is normal expiration?

passive
(brought about by relaxation of inspiratory muscles)

26

what 2 properties allows the lung to recoil to their preinspiratory size during expiration?

elastic connective tissue in the lungs
alveolar surface tension

27

what does the recoil of lungs do to the intra-alveolar pressure?

makes it rise above atmospheric pressure
(Boyle's Law)
this allows air to move from lungs to atmosphere down a pressure gradientq

28

what is a traumatic pneumothorax?

a puncture wound in the chest wall causing a collapsed lung

29

what is a spontaneous pneumothrax?

a hole in the lung itself causing a collapsed lung

30

why do holes in either the chest wall of lung wall cause collapsed lungs?

they permit air to enter the pleural cavity and abolish the transural pressure gradient causing the lung to collapse to its unstretched size

31

what is alveolar surface tension?

attraction between water molecules at liquid air interface on the internal surface of the alveoli producing a force which resists the stretching of the lungs

32

what would happen if the alveoli were lined with water alone on the internal surface?

surface tension would be too strong and the alveoli collapse

33

What is LaPlace's Law

P= 2T/r
where:
P = inward directed collapsing pressure
T = surface tension
r = radius of the alveoli
so collapsing pressure varies directly with surface tension but varies indirectly with to radius

34

what happens to the tendency of the alveoli to collapse if the radius of the alveoli is decreased?

increased tendency to collapse

35

what mixture intersperses between the water molecules lining the alveoli and lowers the alveolar surface tension?

surfactant

36

what is surfactant made of?

a complex misture of lipids and proteins

37

what type of cell secretes surfactant?

type II alveoli

38

in what type of alveoli is surfactant more effective in? (small or big alveoli?)

small alveoli

39

what does surfactant prevent from happening?

the smaller alvoli collapsing and emptying their air contents intp the larger alveoli

40

what causes respiratory distress syndrome of the new born?

premature babies may not have enough pulmonary surfactant and so the baby makes very strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs

41

when is surfactant synthesised in the developing fetal lungs?

late in pregnancy

42

what 3 forces keep the alveoli open? (ie overcome surface tension)

transmural pressure gradient
pulmonary surfactant
alveolar interdependence

43

what happens when an alveolus starts to collapse?

the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus causing it to open again
(alveolar interdependence)

44

what are the accessory muscles of inspiration?

sternocleidomastoid
scalenus

45

what are the major muscles of inspiration?

diaphragma
external intercostal muscles

46

when are the accessory muscles of inspiration used?

during forceful inspiration

47

what are the muscles of active expiration?

internal intercostal muscles
abdominal muscles

48

what device is used to measure lung volumes and capacities?

spirometer

49

what one volume can the spirometer not measure?

residual volume

50

What is the tidal volume? (TV)

volume of air entering or leaving lungs during a single breath

51

what is the inspiratory reserve volume? (IRV)

extra volume of air that can be maximally inspired over and above the typical resting tidal volume

52

what is the average tidal volume? (TV)

500ml

53

what is the average inspiratory reserve volume? (IRV)

3000ml

54

what is the inspiratory capacity? (IC)

the maximal volume of air that can be inspired at the end of a normal quiet expiration
(IC = TV + IRV)

55

what is the average inspiratory capacity? (IC)

3500ml
(500ml + 3000ml)

56

what is the expiratory reserve volume? (ERV)

extra volume of air that can be actively expired by aximal contraction beyond the normal volume of air after a resting tidal colume

57

what is the average expiratory reserve volume? (ERV)

1000ml

58

what is the residual volume? (RV)

minimal volume of air remaining in the lungs even after a maximal expiration

59

what is the average residual volume?

1200ml

60

what is the functional residual capacity? (FRC)

the volume of air in the lungs at the end of a normal expiration
(FRC = ERV +RV)

61

what is the average functional residual capacity?

2200ml
(1000 + 1200ml)

62

what is the vital capacity? (VC)

maximal volume of air that can be moved out during a single breath following a maximal inspiration
(VC = IRV + TV + ERV)

63

what is the average vital capacity?

4500ml
(3000ml + 500ml + 1000ml)

64

what is the total lung capacity? (TLC)

maximal volume of air that the lungs can hold
(TLC = VC + RV
TLC = IRV + TV + ERV + RV)

65

what is the average total lung capacity?

5700ml
(4500ml + 1200ml)
(3000ml + 500ml + 1000ml + 1200ml)

66

what is the forced expiratory volume in 1 second? (FEV1)
[a dynamic volume]

the volume of air that can be expired during the first second in a FVC (forced vital capacity)

67

what is the normal FEV1%?
(FEV1/FVC ratio)

>75%

68

what does spirometry allow you to create?

a volume time curve

69

what 3 things does a volume time curve produced from spirometry allow you to determine?

the FV
FEV1
FEV1%

70

in an obstructive lung disease, what is the FEV%?
(FEV1/FVC ratio)

<75% (reduced)

71

in an obstructive lung disease, what happens to the FEV1 and the FVC?

FEV1- reduced
FVC- normal (4500ml)

72

in a restrictive lung disease, what happens to the FEV1 and the FVC?

FEV1- reduced
FVC- reduced

73

in an restrictive lung disease, what is the FEV%?
(FEV1/FVC ratio)

>75% (normal)

74

what does airway flow vary with?

varies directly with pressure
varies indirectly with resistance
(as pressure increases flow increases. as resisance increases flow decreases.)

75

why does air usually flow in the airways with only a small pressure gradient?

resistance to flow in the airways is normally very low

76

what does parasympathetic stimulation cause in the smooth muscles of the airways?

bronchoconstriction

77

what does sympathetic stimulation cause in the smooth muscles of the airways?

bronchodilation

78

in obstructive disease which is more difficult- expiration or inspiration?

expiration

79

what effect happens during active expiration that causes no problem in normal people but is problematic for patients with airway obstruction?

dynamic airway compression

80

what 2 things does dynamic airway compression cause an increased pressure in?

alveoli
airways

81

what is dynamic airway compression not a problem for normal people?

despite the increased airway resistance, the pressure in the alveoli gets high enough so there is no change in air flow

82

why is dynamic airway compression problematic for patients with airway obstruction?

if there is an airway obstruction, the alveoli pressure wont be high enough to overcome the increased airway resistance- causing air-trapping behind the blackade

83

in addition to obstructed airways, what other type of airways are more likely to collapse?

diseased airways

84

what can aggravate the problem of dynamic airway compression in patients with airway obstruction?

if the patient also has decreased elastic recoil of the lungs
(ie patient with emphysema and obstructed airway caused by COPD)

85

what does a peak flow meter do?

measures the maximum speed at which a patient can move air out of lungs- peak flow rate

86

what does a decrease in peak flow rate show?

possible obstructive lung disease

87

what does peak flow rate in normal adults vary with?

age, sex, height

88

what is pulmonary compliance?

a measure of effort that has to go into stretching or distending the lungs

89

what type of pattern of lung volumes with a decreaed pulmonary compliance show?

restrictive pattern

90

what do pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia and absence of surfactant do to the pulmonary compliance?

decrease pulmonary compliance

91

in restrictive disease which is more difficult- expiration or inspiration?

inspiration

92

what occurs in emphysema?

increased compliance due to loss of elastic recoil (hard to get air out of the lungs- hyperinflation)

93

what physiological factor can cause pulmonary compliance to increase?

age

94

what is the name of the area of the airways where there is inspired air but it is not available for gas exchange?

anatomical dead space

95

Pulmonay ventilation (L)=

tidal volume (L/breath) x respiratory rate (breath/min)

96

what is the normal pulmonary ventilation rate under normal resting conditions?

6L/min

97

why is alveolar ventilation less than pulmonary ventilation?

anatomical dead space

98

alveolar ventilation =

(tidal volume - dead space volume) x Resp Rate

99

what is the normal alveolar ventilation rate under normal resting conditions?

4.2L/min

100

what is pulmonary ventilation?

the volume of air breathed in and out per minute

101

what is alveolar ventilation?

the volume of air exchanged between the atmosphere and the alveoli per minute

102

to increase pulmonary ventilation (ie during exercise) both tidal volume (depth) increases and resp rate increase. which is more advantagous?

tidal volume (depth)
[because of the dead space]

103

what is perfusion?

the rate at which blood is passing through the lungs

104

what is considered as alveolar dead space?

ventilated alveoli which are not adequately perfused with blood

105

physiological dead space =

anatomical death space + alveolar dead space

106

what usually increases significantly in disease? (anatomical or alveolar dead space)

alveolar dead space

107

what type of controls act on the smooth muscle of airways and arterioles to match airflow to blood flow? (ventilation to perfusion matching)

local controls

108

what happens when perfusion > airflow?

increased perfusion causes accumulation of CO2 in the alveoli
the increased CO2 causes decreased airway resistance leading to increased airflow

109

what happens when airflow > perfusion?

increased ventilation causes increased alveolar O2 concentration
increased alveolar O2 concentration causes increased blood flow to match larger airflow

110

what is alveolar oxygen sats are potent pulmonary vasoconstrictors?
(local control)

hypoxia

111

what alveolar oxygen sats are potent pulmonary vasodilators?
(local control)

increased O2

112

what alveolar CO2 sats are potent bronchodilators?
(local control)

increased CO2

113

what alveolar CO2 sats are potent bronchoconstrictors?
(local control)

decreased CO2

114

what tissue cell oxygen sats are potent systemic vasodilators?
(local control)

hypoxia

115

what tissue cell oxygen sats are potent systemic vasoconstrictors?
(local control)

increased O2

116

what 4 factors influence the rate of gas exchange across the alveolar membrane?

1. partial pressure gradient of O2 and CO2
2. diffusion coefficient for O2 and CO2
3. surface area of alveolar membrane
4. thickness of alveolar membrane

117

what is Dalton's law of parital pressures?

the total pressure exerted by a gaseous mixture = the sum of the partial pressures of each individual component in the gas mixture
(P total = P1 + P2 + P3...)

118

what is the partial pressure of a gas in a mixture of gases that don't react with each other?

the pressure that gas wold exert if it occupied the total volume for the mixture in the absence of the other components

119

what contributes to about 47mmHg of the total pressure in the lungs?

water vapour pressure

120

what is the pressure of inspired air?
(without the water vapour)

713mmHg
(760-47mm)

121

considering oxygen makes up 21% of the air concentration, what is the the partial pressure of inspired oxygen (PiO2)?
[remember without water vapour, the pressure of inspired air = 712mmHg]

0.21 x 731= 150mmHg

122

What is the alveolar gas equation?

PAO2 = PiO2- [PaCO2/0.8]

123

what is the normal arterial PCO2?

40 mmHg

124

at a normal arterial PCO2 what is the PAO2?

PAO2 = 150mmHg - [40/0.8]
=100mHg

125

what is the PAO2?

the partial pressure of O2 in alveolar air

126

what is the PiO2?

the partial pressure of O2 in inspired air

127

what is PaO2?

the partial pressure of O2 in arterial blood

128

what is PaCO2?

the partial pressure of CO2 in arterial blood

129

what does the respiratory exchange ratio (RER) mean?

the ratio of CO2 produced and O2 consumed
CO2:O2

130

for someone eating a mixed diet what is the average respiratory exchange ratio?

0.8

131

how do you convert mmHg pressure to kPa?

kPa = mmHg/7.5

132

what is the normal venous pressure of oxygen?

40mmHg

133

what is the O2 partial pressure gradient across the pulmonary capillaries (from alveoli to blood)?

60mmHg (8kPa)
(100mmHg - 40mmHg)

134

what is the normal venous pressure of CO2?

46mmHg

135

what is the CO2 partial pressure gradient across the pulmonary capillaries (from blood to alveoli)?

6mmHg (0.8kPa)
(46mmHg-40mmHg)

136

what 2 partial pressure of oxygen are the same?

PAO2 and PaO2 = 100mmHg

137

what 2 partial pressures of CO2 are the same?

PAO2 and PaO2 = 40mmHg

138

what is the O2 partial pressure gradient across systemic capillaries (from blood to tissue cell)?

>60mmHg (>8kPa)
(100mmHg - <40mmHg)

139

what is the CO2 partial pressure gradient across systemic capillaries (from tissue cell to blood?)

>6mmHg (>0.8kPa)
(46mmHg - <40mmHg)

140

what is the diffusion co-efficient?

the solubility of gas in membranes

141

compare the diffusion co-efficients of CO2 and O2?

CO2 diffusion coefficient = 20x diffusion coefficient for O2
(ie CO2 is more soluble in membranes than O2)

142

why is a small gradient between PAO2 and PaO2 normal?

ventilation-perfusion match is usually not perfect

143

what does a big gradient between PAO2 and PaO2 indicate?

problems with gas exchange in the lungs or a right to left shunt in the heart

144

what is Fick's Law of diffusion?

the amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportionate to its thickness

145

what type of alveolar cells does gas exchange occur across?

type 1 alveolar cells

146

what happens to the rate of gas transfer across the alveolar membrane as the partial pressure gradient increases?

rate of gas transfer increases

147

what happens to the rate of gas transfer across the alveolar membrane as the surface area increases?

rate of gas transfer increases

148

what happens to the rate of gas transfer across the alveolar membrane as the thickness increases?

rate of gas transfer decreases

149

what happens to the rate of gas transfer across the alveolar membrane as the diffusion coefficient increases?

rate of transfer increases

150

what is the main influence for the rate of oxygen transfer across the alveolar membrane?

the partial pressure gradient

151

what is the main influence for the rate of carbon dioxide transfer across the alveolar membrane?

the diffusion coefficient

152

what are the 7 non-respiratory functions of the respiratory system?

1. route for water loss and heat elimination
2. enhances venous return
3. helps maintain normal acid-base balance
4. enables speech, singins and other vocalizations
5. defends agasint inhaled foreign matter
6. remoes, modifies, activates or inactivates various materials passing through the pulmonary circulation
7. nose serves as the organ of smell.

153

What is Henrys Law?

the amount of a given gas dissolved in a given type and volume of liquid (at a constant temp) is proportional to the partial pressure of the gas in equilibrium with the liquid

154

what happens to the concentration of gas in a liquid, if the partial pressure of the gas in equilibrium to the liquid is increased?

the concentration of gas in a liquid will also increase

155

when a gas is in a equilibrium between the gaseous phase and the liquid phase, what is the partial pressure of the gas in solution equal to?

the partial pressure of the gaseous phase

156

as the partial pressure increases, what happens to the amount of O2 dissolved in the blood? (Henry's law)

dissolved O2 increases

157

in what forms is O2 present in the blood?

bound to haemoglobin (98.5%)
physically dissolved (1.5%

158

how many haem groups does each haemoglobin molecule contain?

4 haem groups

159

when is haemoglobin considered fully saturated?

when all the Hb present is carrying its maximum O2 load

160

what is the primary factor which determins the percent saturation of haemoglobin?

PO2

161

what is the average resting PO2 at systemic capillaries?

5.3kPa

162

what is the normal PO2 at pulmonary capillaries?

13.3kPa

163

what is the DO2I?

Oxygen delivery index
(ml/min/meter^2)

164

DO2I =

CaO2 x Cl

165

what is CaO2?

oxygen content of arterial blood (ml/L)

166

what is Cl?

the cardiac index - related the cardiac output to the body surface area (L/min/meter^2)

167

what is the normal range for cardiac index? (CI)

2.4-4.2L/min/meter^2

168

CaO2 =

1.34 x [Hb] x SaO2

169

one gram of haemoglobin carries how much oxygen when fully saturated? (in millilitres)

1.34ml

170

what is SaO2?

the percentage of Hb saturated with O2?

171

what is SaO2 determined by?

PO2

172

what 3 broad reasons can oxygen delivery to the tissues be impaired by?

respiratory disease
heart failure
anaemia

173

what does binding of one molecule of oxygen (O2) to Hb do to the affinity of Hb for O2?

increases the affinity of Hb for O2
(co-operativity, sigmoid curve)

174

what happens to the haemoglobin molecule when all sites are occupied?

flattens

175

how many chains does haemoglobin contain?

2 alpha chains
2 beta chains
(4 in total)

176

what is the functional ion of a haem group?

iron (Fe++)

177

What does the Bohr effect do?

causing a shift of the haemoglobin saturation sigmoid curve to the right (ie decreased affinity for oxygen and therefore increased release of O2)

178

what 4 factors cause the Bohr effect?

increased PCO2
increased [H+]
increased temp
increase 2,3-biphosphoglycerate

179

where does the Bohr effect usually hapen?

at tissues
(they want the increased release of oxygen from haemoglobin)

180

how many haem groups does myoglobin have per molecule?

one haem group

181

which has cooperative binding- haemoglobin or myoglobing?

haemoglobin

182

what shape is a haemoglobin dissociation curve?

sigmoid

183

what shape is a myoglobin dissociation curve?

hyperbolic

184

when does myoglobin release O2?

at a very low PO2

185

what is the function of myoglobin?

provides short-term storage for O2 for anaerobic conditions

186

where is myoglobin physiologically present?

skeletal and cardiac muscles

187

what does presence of myoglobin in the blood indicate?

muscle damage

188

what are the 3 ways CO2 is transported in the blood?

solution (10%)
as bicarbonate (60%)
as carbamino compounds (30%)

189

compare the solubility of carbon dioxide to oxygen?

CO2 is 20 times more soluble than O2

190

what is the equation for the transformation of carbon dioxide into bicarbonate?

CO2 + H2O (reversible with) H2CO3 (reversible with) H+ + HCO3-

191

what enzyme converts CO2 + H20 to H2CO3?

carbonic anhydrase

192

where does the conversion of carbon dioxide to bicarbonate take place?

in red blood cells

193

a byproduct of the conversion of cardbon dioxide to bicarbonate is a H+ atom, what does this bind with?

Hb to make HbH

194

how are carbamino compounds formed?

by combination of CO2 with terminal amine groups in blood proteins

195

what is formed when carbon dioxide combines with the globulin of haemoglobin?

carbamino-haemoglobin

196

in which form is the haemoglobin more readily able to bind CO2?

reduced Hb (ie with no oxygen molecules attached) more readily binds with CO2 than HbO2

197

What is the Haldane effect?

removing O2 from Hb increases the ability of Hb to pick up CO2 and CO2 generated H+

198

what do the Bohr effect and the Haldane effect work in synchrony to facilitate?

the liberation of O2 and the uptake of CO2 and CO2 generated H+ at tissues

199

what neurones generate the breathing rhythm (act as a pacemaker) for respiration?

pre-botzinger complex in the medullary respiratory centre

200

what causes contraction of inspiratory muscles and therefore causes inspiration?

firing of the dorsal respiratory group neurones in the medullary respiratory centre

201

what causes relaxation of inspiratory muscle and therefore causes passive expiration?

ceased firing of the dorsal respiratory group neurones in the medullary respiratory centre

202

what neurone group does increased firing of the dorsal respiratory group neurones in the medullary respiratory centre excite?

the ventral respiratory group neurones

203

what causes contraction of internal intercostals and abdominal muscles and therefore causes active/forceful expiration?

firing of the ventral respiratory group neurones in the medullary respiratory centre

204

the rhythm that is generated in the medulla can be modified from neurones where else in the brain?

the pons

205

What signal from the pons stimulates the termination of inspiration? (ie causes dorsal neurones to stop firing)

firing of neurones from the pneumotaxic centre of the pons

206

when is the pneumotaxic centre in the pons stimulated?

when dorsal respiratory neurones fire

207

what type of breathing occurs without the pneumotaxic centre?

apneusis

208

describe apneusis?

breathing is prolonged inspiratory gasps with brief expiration

209

what is the main function of the pneumotaxic centre?

inhibition of inspiration

210

what impulses excite the dorsal neurones in the medullary respiratory centre?

firing from neurones from the apneustic centre in the pons

211

what is the main function of the apneustic centre?

prolongs inspiration

212

what are the 4 types of involuntary (reflex) modifications of breathing?

1. Hering-Breuer Reflex
2. joint receptors reflex
3. stimulation of respiratory centre
4. cough reflex

213

what 5 ways can the respiratory centre be involuntary stimulated to increase ventilation during exercise?

body movement
temperature
adrenaline
impulses from cerebral cortex
accumulation of CO2 and H+ generated by active muscles

214

what is the Hering-Breuer reflex?

pulmonary stretch receptors detect how much the lung has expand and when the lung has inflated sufficiently they send an afferent trigger which inhibits inspiration

215

what is the purpose of the Hering-Breuer reflex?

to prevent over-inflation of the lungs,
but not active during normal respiratory cycle

216

What is the joint receptor reflex?

impulses from moving limbs reflexly increase breathing

217

what does the joint receptor reflex contribute to?

the necessary increased ventilation during exercise

218

why does recovery phase of exercise take time for ventilation rate to return to normal?

takes time to wash the chemical triggering increased ventilation out

219

what is the function of the cough reflex?

helps clear airways of dust, dirt or excessive secretion

220

when is the cough reflex activated?

irritation of the airways or tight airways

221

what is the events that occur during a cough reflex?

1. irritation of airways/tight airways
2. afferent discharge
3. short intake of breath
4. closure of larynx
5. contraction of abdominal muscles to increase intra-alveolar pressure
6. opening of the larynx
7. expulsion of air at high speed

222

what type of feedback control is the chemical control of respiration?

negative feedback

223

what do chemoreceptors do?

sense the values of gas tensions

224

what are the controlled variables in the chemical feedback control of respiration?

blood gas tensions

225

where are peripheral chemoreceptors located?

arch of aorta
carotid bodies

226

what do peripheral chemoreceptors sense?

tension of oxygen and carbon dioxide
[H+] in the blood

227

where are central chemoreceptors located?

near the surface of the medulla of the brainstep

228

what do central chemoreceptors respond to?

[H+] of the cerebrospinal fluid (CSF)

229

how is the cerebrospinal fluid separated from the blood?

by the blood-brain barrier

230

what is the blood-brain barrier impermeable to?

H+
HCO3-
proteins

231

what diffuses readily across the blood brain barrier?

CO2

232

what happens when CO2 diffuses across the blood brain barrier?

dissociated into H+ ions
as there is a low protein content of the CSF the ions produced arent buffered well and so stimulate the central chemoreceptor

233

what is the term used to describe high carbon dioxide concetrations in the blood?

hypercapnia

234

as hypercapnia increases slightly what happens to ventilation?

increases rapidly:
to remove excess CO2

235

what happens to the respiratory centre neurones when there is severe hypoxia?

become depressed and so there is a poor ventilation

236

as a general trend, what happens when PO2 increases?
(ignore extreme hypoxia)

ventilation decreases

237

as altitude increases what happens to the partial pressure of oxygen?

decreases

238

what type of chemoreceptors cause the effect of hypoxic drive of respiration?

peripheral chemoreceptors
(only they can detect oxygen levels, central only detect CO2 levels through CO2 generated H+)

239

when is the hypoxic drive of respiration stimulated?

when PaO2 < 8kPa

240

when does the hypoxic drive of respiration become important?

in patients with chronic CO2 retention (ie COPD)
high altitudes

241

why does hypoxia at high altitudes occur?

decreased partial pressure of inspired oxygen (PiO2)

242

what is the acute response to hypoxia at high altitudes?

hyperventilation + increased cardiac outpus

243

what are 5 chronic adaptations to high altitude hypoxia?

1. polycythaemia
2. increase 2,3-biphosphoglycerate produced within RBC
3. increased number of capillaries
4. increased number of mitochondria
5. kidneys conserve aid

244

why is polycythaemia a useful adaptation to high altitude hypoxia?

increases O2 carrying capacity of the blood

245

why is increased 2,3-biphosphoglycerate production within the RBS a useful adaptation to high altitude hypoxia?

allows O2 to be offloaded more easily into tissues
(Bohr's effect)

246

why is increased number of capillaries a useful adaptation to high altitude hypoxia?

allows blood to diffuse more easily

247

why is increased number of mitochondria a useful adaptation to high altitude hypoxia?

allows O2 to be used more efficiently

248

why is metabolic conservation of acid a useful adaptation to high altitude hypoxia?

decreases pH (metabolic acidosis) which allows O2 to be ofloaded more easily into tissues
(Bohr's effect)

249

what receptors cause the H+ drive of respiration?

peripheral chemoreceptors

250

what is the function of the H+ drive of resiration?

adjusts for acidosis caused by the addition of non-carbonic acid H+
(eg lactic acid or diabetic ketoacidosis)

251

what does the H+ drive of respiration cause?

hyperventilation and incresaes elimination of CO2 from the body (reduces body acid content)

252

what receptors cause the CO2 drive of respiration?

central chemoreceptors