Physiology Flashcards
(252 cards)
1
Q
what is the internal respiration equation?
A
food + oxygen = energy + carbon dioxide (+ water)
consumption of oxygen and production of carbon dioxide
2
Q
what does external respiration refer to?
A
the exchange of oxygen and carbon dioxide between external environment and the cells of the body
3
Q
how many steps are involved in external respiration?
A
4
4
Q
what is the 1st step of external respiration?
A
ventilation
5
Q
what is the 2nd step of external respiration?
A
gas exchange between alveoli and blood
6
Q
what is the 3rd step of external respiration?
A
gas transport in the blood
7
Q
what is the 4th step of external respiration?
A
gas exchange at tissue level
8
Q
what does ventilation (1st step of external respiration) involve?
A
the mechanical process of gas exchange between the armosphere and the alveoli
9
Q
what does ‘gas exchange between alveoli and blood’ (2nd step of external respiration) involve?
A
exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries
10
Q
what does ‘gas transport in the blood’ (3rd step of external respiration) involve?
A
the binding and transport of oxygen and carbon dioxide in the circulating blood
11
Q
what does ‘gas exchange at tissue level’ (4th step of external respiration) involve?
A
the exchange of oxygen and carbon dioxide between the blood in the systemic circulation and the body cells
12
Q
what 3 body systems are involved in external respiration?
A
respiratory system
cardiovascular system
haematology system
13
Q
What is Boyle’s Law?
A
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
Q
air flows down a pressure gradient ___ pressure to a region of ___ pressure
A
high pressure to a region of low pressure
15
Q
when is the intra-alveolar pressure equivalent to the atmospheric pressure?
A
before inspiration
16
Q
What does expansion of the thorax and lungs do to the intra-alveolar pressure?
A
makes it fall below atmospheric pressure (Boyle’s Law)
this allows air to move from atmosphere into lungs down pressure gradient
17
Q
what 2 forces hold the thoracic wall and the lungs in close opposition?
A
- intrapleural fluid cohesiveness
2. the negative intrapleural pressure
18
Q
how does the intrapleural fluid keep thoracic wall and lungs in close opposition?
A
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
Q
how does the negative intrapleural pressure keep the thoracic wall and lungs in close opposition?
A
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
Q
what 3 pressures are important in ventilation?
A
atmospheric pressure
intra-alveolar pressure
intrapleural pressure
21
Q
what is the atmospheric pressure at sea level?
A
760mmHg
22
Q
what is usually the intrapleural pressure?
A
756mmHg
23
Q
when the external intercostal muscle contract what do they cause?
A
elevation of the ribs, causing the sternum to move upwards and forwards- increases AP dimension of thoracic cavity
24
Q
what type of process is inspiration?
A
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?
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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
