Respiratory Physiology Flashcards
1
Q
<p>What does internal respiration refer to?</p>
A
<p>The intracellular mechanisms which consumes O2 and produces CO2</p>
2
Q
<p>External Respiration</p>
A
<p>Sequence of events that lead to the exchange of O2 and CO2 between the external environment and cells of the body</p>
3
Q
<p>How many steps does external respiration involve?</p>
A
<p>Four steps</p>
4
Q
Explained Steps of External Respiration
A
<p>1. Ventilation - gas exchange between the atmosphere and air sacs in the lungs
2. Exchange - of O2 and CO2 between air in alveoli and blood coming to lungs (in pulmonary arteries)
3. Transport - of O2 and CO2 in the blood between the lungs and the tissues
4. Exchange - of O2 and CO2 between the blood in the systematic capillaries and the body cells</p>
5
Q
Summarised Four Steps of External Respiration
A
- Ventilation
- Gas exchange between alveoli and blood
- Gas transport in the blood
- Gas exchange at the tissue level
6
Q
What are the four body systems involved in external respiration?
A
- Respiratory system
- Cardiovascular system
- Haematology system
- Nervous system
7
Q
Definition of Ventilation
A
The mechanical process of moving air between the atmosphere and alveolar sacs
8
Q
Boyle’s Law
A
- At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas
To put it simply…
- As the volume of gas increases, the pressure exerted by the gas decreases
9
Q
For air to flow into the lungs during inspiration the intra-alveolar pressure must become _____ than the atmospheric pressure
A
less
10
Q
What are the two distinct phases in respiration?
A
- Inspiration (inhalation)
- Expiration (exhalation)
11
Q
During inspiration the _____ and _____ expand as a result of what?
A
- Thorax
- Lungs
- Contraction of inspiratory muscles
12
Q
Where is the thorax?
A
Region of the body formed by the…
- Sternum
- Thoracic Vertebrae
- Ribs
13
Q
What are the two forces that hold the thoracic wall and lungs in close opposition?
A
(1) The intrapleural fluid cohesiveness
(2) The negative intrapleural pressure
14
Q
What is meant by the INTRAPLEURAL FLUID COHESIVENESS
A
- Water molecules in the inrapleural fluid are attracted to each other and resist being pulled apart
- So membranes stick together
15
Q
What is meant by the NEGATIVE INTRAPLEURAL PRESSURE
A
- The sub-atmospheric intrapleural pressure create a transmural pressure gradient across the lung wall and chest wall
- Lungs are forced to expand outwards while the chest is forced to squeeze inwards
16
Q
Three pressures important in ventilation
A
- Atmospheric pressure
- Intra-alveolar (intrapulmonary) pressure
- Intrapleural (intrathoracic) pressure
17
Q
Inspiration is an ____ process depending on _____ _______
A
- Active
- Muscle contraction
18
Q
Volume of the thorax is increased _______ by contraction of the ________ flattening out its dome shape
A
- vertically
- diaphragm (major inspiratory muscle)
19
Q
What muscle contraction lifts the ribs and moves out the sternum?
A
The external intercostal muscle contraction
“bucket handle” mechanism
20
Q
During inspiration the chest wall and lungs are…
A
stretched
21
Q
Increase in size of lungs during inspiration does what to the intra-alveolar pressure?
A
Causes the intra-alveolar pressure to fall
22
Q
Why does the intra-alveolar pressure fall when the size of lungs increases?
A
The air molecules become contained in a larger volume (BOYLE’S LAW)
23
Q
What occurs after the increase in size of lungs during inspiration?
A
- Air then enters the lungs down its pressure gradient until the intra-alveolar pressure becomes equal to atmospheric pressure
24
Q
Normal expiration is a ______ process brought about by the ______ of inspiratory muscles
A
- Passive process
- Relaxation
25
Process of Expiration
- Chest wall and stretched lungs recoil to preinspiratory size because of their elastic properties
- Recoil of lungs makes the intra-alveolar pressure rise as air molecules are contained in a smaller volume (BOYLE'S LAW)
- Air then leaves lungs down pressure gradient until intra-alveolar pressure becomes equal to atmospheric pressure
26
What is Pneumothorax
Air in the pleural space (normally filled with fluid not air)
27
Pneumothorax can be...
-
-
- Spontaneous
- Traumatic
- Iatrogenic
28
How does pneumothorax occur?
- Air enters the pleural space from outside or from the lungs
- This air can abolish the transmural pressure gradient leading to the lung collapsing
29
What can happen with pneumothorax?
The lung can collapse
30
Small pneumothorax can be what?
Symptomatic
31
What are the symptoms of pneumothorax?
- Shortness of breath
| - Chest pain
32
What are the physical signs of pneumothorax?
- Hyperresonant
- Percussion Note
- Decreased/absent breath sounds
33
What causes the lungs to recoil during expiration?
- Elastic connective tissue in the lungs (whole structure bounces back into shape)
- Alveolar surface tension
34
What is alveolar surface tension?
- Attraction between water molecules at liquid air interface
35
What does alveolar surface tension produce?
Produces a force which resists the stretching of the lungs
36
What would happen if the alveoli were lined with water alone
The surface tension would be too strong so the alveoli would collapse
37
What does the law of LaPlace state?
The smaller alveoli (with smaller radius - r) have a higher tendency to collapse
38
What is pulmonary surfactant?
A complex mixture of lipids and proteins secreted by type II alveoli
39
What does pulmonary surfactant do?
Pulmonary surfactant lowers the surface tension of smaller alveoli more than that of large alveoli
40
What is the purpose of pulmonary surfactant lowering the surface tension of smaller alveoli
Prevents the smaller alveoli from collapsing and emptying their air contents into larger alveoli
41
LaPlace's Law Formula
P = 2T / r
42
What is P in LaPlace's Law?
The inward directed collapsing pressure
43
What is T in LaPlace's Law?
Surface Tension
44
What is r in LaPlace's Law?
Radius of the bubble
45
Developing fetal lungs are unable to do what?
Unable to synthesize surfactant until late in preganancy
46
Premature babies may not have enough of what?
Pulmonary surfactant
47
Premature babies not having enough pulmonary surfactant causes what?
Respiratory distress syndrome of the new born
48
Respiratory distress syndrome means the baby has to do what to breathe?
Make very strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs
49
What is another factor that keeps the alveoli open?
The Alveolar Interdependence
50
What is the alveolar interdependence
- If and alveolus starts to collapse, surrounding alveoli are stretched
- Surrounding alveoli then recoil exerting expanding forces in the collapsing alveolus to open it
51
Name the forces keeping the alveoli open
- Transmural pressure gradient
- Pulmonary surfactant
- Alveolar Interdependence
52
Name the forces promoting alveolar collapse
- Elasticity of stretched lung connective tissue
| - Alveolar surface tension
53
What are the major inspiratory muscles?
- Diaphragm
| - External Intercostal Muscles
54
What are the Accessory Muscles of Inspiration?
| contracts only during forceful inspiration
- Sternocleidomastoid
- Scalenus
- Pectoral
55
What are the muscles of active expiration?
| contracts only during active expiration
- Abdominal Muscles
| - Internal Intercostal Muscles
56
What is IC?
Inspiratory capacity
| - Maximum volume of air that can be inspired at the end of a normal quiet expiration
57
What is ERV?
Expiratory Reserve Volume
- Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume
58
What is RV?
Residual Volume
| - Minimum volume of air remaining in the lungs even after a maximal expiration
59
What is VC?
Vital Capacity
| - Maximum volume of air that can be moved out during a single breath following a maximal inspiration
60
What is IRV?
Inspiratory Reserve Volume
| - Extra volume of air that can be maximally inspired over and above the typical resting tidal volume
61
What is TV?
Tidal Volume
| - Volume of air entering or leaving lungs during a single breath
62
What is FRC?
Functional Residual Capacity
| - Volume of air in lungs at the end of normal passive expiration
63
What is TLC?
Total Lung Capacity
| - Total volume of air the lungs can hold
64
What is the average value of tidal volume?
0.5L
65
What is the average value of inspiratory reserve volume?
3.0L
66
Average value of expiratory reserve volume?
1.0L
67
Average value of residual volume?
1.2L
68
What is the inspiratory capacity average value?
3.5L
69
What is the inspiratory capacity equation?
IC = IRV + TV
70
What is the functional residual capacity equation?
FRC = ERV + RV
71
What is the functional residual capacity average value?
2.2L
72
What is the vital capacity equation?
VC = IRV + TV + ERV
73
What is the vital capacity average value?
4.5L
74
What is the total lung capacity equation?
TLC = VC + RV
75
What is the total lung capacity average value?
5.7L
76
Residual volume cannot be measured by what?
Cannot be measured by spirometry
77
If residual volume cannot be measured by spirometry what else cannot be measured?
Total lung volume
78
Residual volume increases when...
Elastic recoil of the lungs is lost e.g. in emphysema
79
What does a volume time curve allow you to determine?
- Forced Vital Capacity (FVC)
| - Forced Expiratory Volume in one second (FEV1)
80
What is forced vital capacity (FVC)?
The maximum volume that can be forcibly expelled from the lungs following a maximum inspiration
81
What is forced expiratory volume in one second (FEV1)?
The volume of air that can be expired during the first second of expiration in a forced vital capacity (FVC) determination
82
What is the FEV1/FVC ratio?
The proportion of forced vital capacity that can be expired in the first second
83
How to calculate the FEV1/FVC ratio?
- (FEV1/FVC) X 100%
| - Normally more than 70%
84
Dynamic Lung Volumes are useful in the diagnosis of what?
Obstructive and Restrictive lung disease
85
What is the formula to calculate airway resistance?
F = deltaP / R
- F = flow
- P = pressure
- R = resistance
86
Resistance to flow in the airway is normally very ______ and therefore air moves with a small _____ _____
- low
| - pressure gradient
87
What is primary determinant of airway resistance?
- The radius of the conducting airway
88
What does parasympathetic stimulation do to the bronchi?
Causes bronchoconstriction
89
What does sympathetic stimulation do to the bronchi?
Causes bronchodilation
90
REMEMBER
| Sympathetic stimulation does what?
Fight or flight
| Reacts to stresses
91
REMEMBER
| Parasympathetic stimulation does what?
Rest and digest
92
What is a disease state?
- A disordered or incorrectly functioning organ
- E.g. COPD or asthma
- Can cause significant resistance to airflow
- Makes expiration more difficult than inspiration so more and more air gets trapped in the lungs
93
What happens to the airways during inspiration?
- Pulled open by the expanding thorax
| - Intrapleural pressure falls
94
Where is the pleural cavity?
Between the parietal pleura (outter layer) attached to the chest wall and the visceral pleura (inner layer attached to lungs)
95
What happens to the chest during expiration?
- The chest recoils
| - Intrapleural pressure rises
96
What is the intrapleural pressure?
- The pressure within the pleural cavity
| - Pressure within the pleural cavity is slightly less than atmospheric pressure normally
97
What does pressure being applied to the alveolus do?
Helps push air out of the lungs
| - Pressure applied not always desirable as can compress the alveolus
98
Rising pleural pressure during active expiration does what?
Compresses the alveoli and the airway
99
Dynamic airway compression makes active expiration to be more dificult in patients with...
- Airway obstruction
| - Causes no problems in normal people
100
Increased airway resistance causes an increase in airway pressure upstream, what does this help with?
Helps open the airways by increasing the driving pressure between the airways and the alveolus (i.e. the pressure downstream)
101
If there is an obstruction in the airways (e.g. COPD or asthma), what happens to the driving pressure between the alveolus and airway
- The pressure is lost over the obstructed segment
- Causes a fall in airway pressure along airway downstream
- Resulting in airway compression by the rising pleural pressure during active expiration so collapse
102
Problem of obstructed airways becomes worse if...
Patient also has decreased elastic recoil of lungs
103
What is the purpose of a peak flow meter?
- Gives an estimate of peak flow rate which assesses airway function
- Useful in patients with obstructive lung disease
104
How is peak flow rate measured?
- Measured by giving the patient a short sharp blow into the peak flow meter
- Best of three attempts usually taken
- Varies with age and height
105
What is pulmonary compliance?
A measure of effort that has to go into stretching or distending the lungs
106
What is pulmonary compliance measured in?
Volume change per unit of pressure change across the lungs
107
What factors decrease pulmonary compliance?
- Pulmonary fibrosis
- Pulmonary oedema
- Lung collapse
- Pneumonia
- Absence of surfactant
108
Decreased pulmonary compliance means what?
- Greater change in pressure is needed to produce a given change in volume
- Causes shortness of breath especially on exertion
- May cause a restrictive pattern of lung volumes in spirometry
109
When may pulmonary compliance become increased?
If the elastic recoil of the lungs is lost
| - Occurs in emphysema, patients have to work harder to get the air out of the lungs (hyperinflation of lungs)
110
Compliance increases with what?
Increasing age
111
For quiet breathing, what percentage of total energy expenditure is required?
3% of total energy expenditure
112
What is the phrase used to describe how lungs operate?
"half full"
113
In what situations is work of breathing increased in?
- When pulmonary compliance is decreased
- Airway resistance increased
- Elastic recoil decreased
- When there is a need for increased ventilation
114
What is pulmonary ventilation?
Volume of air breathed in and out per minute
115
What is alveolar ventilation?
Volume of air exchanged between the atmosphere and alveoli per minute
116
What is anatomical deadspace?
Area where air remains in the airways which is not available for gas exchange
117
How is pulmonary ventilation (L) calculated?
Pulmonary ventilation = tidal volume (L/breath) x respiratory rate (breath/min)
118
Alveolar ventilation is less than pulmonary ventilation due to the presence of...
Anatomical dead space
119
How is alveolar ventilation calculated?
Alveolar ventilation
| = (tidal volume - dead space volume) x respiratory rate
120
To increase pulmonary ventilation...
Both the depth (tidal volume) and the rate of breathing (BR) increase
121
Why is it more advantageous to increase the depth of breathing?
Because of dead space
122
The transfer of gases between the body and atmosphere depends upon what two features?
- Ventilation
| - Perfusion
123
What is perfusion?
The rate at which blood is passing through the lungs
124
What is ventilation?
The rate at which gas is passing through the lungs
125
What is alveolar dead space?
Ventilated alveolar which are not adequately perfused with blood
126
What is dead space like in healthy people?
- Very small dead space
| - Little performance
127
What is physiological dead space?
Anatomical dead space + alveolar dead space
128
When could the alveolar dead space increase significantly?
In disease
129
Local controls in the ventilation perfusion match in the lungs act on what?
- Act on smooth muscles of airways and arterioles
| - To match airflow to blood flow
130
Accumulation of CO2 in alveoli can be a result of
Increased perfusion
131
What does accumulation of CO2 in alveoli do?
Decreases airway resistance
| Leads to increased airflow
132
Increase in alveolar O2 can be a result of what?
Increased ventilation
133
What does increase in alveolar O2 do?
- Increase ventilation
- Causes pulmonary vasodilation
- Increased blood flow to match larger airflow
134
Name the areas in which perfusion is greater than ventilation?
- CO2 increases
- O2 decreases
- Dilation of local airways
- Constriction of local blood vessels
- Airflow increases
- Blood flow decreases
135
Name the areas in which ventilation is greater than perfusion?
- CO2 decreases
- O2 increases
- Constriction of local airways
- Dilation of local blood vessels
- Airflow decrease
- Blood flow increase
136
What is the effect of O2 on pulmonary arterioles?
- Decreased O2 means vasoconstriction
| - Increased O2 means vasodilation
137
What is the effect of O2 on systemic arterioles?
- Decreased O2 means vasodilation
| - Increased O2 means vasoconstriction
138
What are the four factors that influence the rate of gas exchange across alveolar membrane?
- Partial pressure gradient of O2 and CO2
- Diffusion coefficient for O2 and CO2
- Surface area of the alveolar membrane
- Thickness of the alveolar membrane
139
What does the partial pressure of a gas determine?
Determines the pressure gradient for that gas
140
What is Dalton's Law of Partial Pressures?
The total pressure exerted by a gaseous mixture
equals
The sum of partial pressures of each individual component in the gas mixture
141
P(total) =
P1 + P2 + ... + Pn
142
What is the partial pressure of gas?
Pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume
Occupied by the mixture at a given temperature
143
How to calculate the partial pressure of oxygen in the alveolar air
PAO2 = PiO2 - [PaCO2/0.8]
144
What is PAO2?
Partial pressure of O2 in alveolar air
145
What is PiO2?
Partial pressure of O2 in inspired air
146
What is PaCO2?
Partial pressure of CO2 in arterial blood
147
What is the 0.8 in the alveolar gas equation?
Respiratory exchange ratio
148
The air in the respiratory tract is saturated with what?
Water
149
What is the O2 partial pressure gradient from alveoli to blood across pulmonary capillaries?
60 mm Hg (8 kP)
150
What is the CO2 partial pressure gradient from alveoli to blood across pulmonary capillaries?
6 mm Hg (0.8 kP)
151
What is the O2 partial pressure gradient from blood to tissue cell across systemic capillaries?
> 60 mm Hg (8 kP)
152
What is the CO2 partial pressure gradient from tissue cell to blood across systemic capillaries?
> 6 mm Hg (0.8 kP)
153
The partial pressure gradient for CO2 is much ______ than that for O2
smaller
154
What offset the difference in partial pressure gradient for CO2 and O2?
- CO2 is more soluble in membranes than O2
155
What is the diffusion coefficient for a gas?
The solubility of gas in membranes
156
How much more is the diffusion coefficient for CO2 than that of O2?
20 times more
157
How big is the gradient between alveolar PO2 (PAO2) and arterial PO2 (PaO2)?
Small gradient
158
What would a big gradient between PAO2 and PaO2 indicate?
- Problems with gas exchange in the lungs
| - Right to left shunt in the heart
159
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
- inversely proportional to thickness of the sheet
160
The lungs have a very extensive ______ ______ network
Pulmonary capillary
161
Remember: The pulmonary circulation receives the entire what?
Receives the entire cardiac output
162
What are the three respiratory membranes?
- Alveoli
- Pulmonary Capillaries
- Narrow Interstitial Space
163
Name 3 non-respiratory functions of the respiratory system
- Route for water loss and heat elimination
- Enhances venous return
- Helps maintain normal acid-base balance
- Enables speech, singing and other vocalisations
- Defends agains inhaled foreign matter
- Removes, modifies, activates or inactivates various materials passing through the pulmonary circulation
- Nose serves as the organ of smell
164
What does Henry's Law State?
The amount of a given gas dissolved in a given type and volume of liquid at a constant temperature is:
- proportional to the partial pressure of the gas in equilibrium with the liquid
165
According to Henry's law, if the partial pressure in the gas phase is increased the concentration of the gas in the liquid phase would...
Increase proportionally
166
The partial pressure of a gas in solution is its partial pressure in the gas mixture with which it is in...
equilibrium
167
The O2 amount dissolved in blood is proportional to what?
Proportional to partial pressure (Henry's Law)
168
Most O2 in the blood is transported bound to what?
Bound to haemoglobin in the red blood cells
169
What two forms is O2 present in the blood?
- Bound to haemoglobin
| - Physically dissolved (very little O2)
170
Haemoglobin can form a reversible combination with...
O2
171
Each haemoglobin (Hb) molecule contains how many haem groups?
4 haem groups
172
Haemoglobin is considered _______ _______ when all the Hb present is carrying its maximum _____ _____
- Fully saturated
| - O2 Load
173
Each haem group ______ binds to one _____ ______
- reversibly binds
| - O2 molecule
174
What is the Po2?
The primary factor which determines the percent saturation of haemoglobin with O2
175
How to calculate the oxygen delivery index (DO2I)?
DO2I = CaO2 x CI
176
What is CaO2?
Oxygen content of arteril blood (ml/L)
177
What is CI?
Cardiac Index (L/min/metre^2)
178
How is the oxygen delivery index (DO2I) measured?
ml/min/metre^2
179
Cardiac index relates the cardiac output to the...
Body surface area
180
Oxygen delivery to the tissues is a function of...
- Oxygen content of arterial blood
| - Cardiac output
181
How do you calculate the oxygen content of arterial blood (CaO2)?
CaO2 = 1.34 x [HB] x SaO2
182
Why 1.34 when calculating the oxygen content of arterial blood?
One gram of Hb carries 1.34ml of O2 when fully saturated
183
What is [Hb}?
Haemoglobin concentration (gram/L)
184
What is SaO2?
%Hb saturated with O2
| - determined by PO2
185
What determines the O2 content of arterial blood?
- Determined by the haemoglobin concentration [Hb]
| - Saturation of Hb with O2
186
Oxygen delivery to the tissues can be impaired by what?
- Respiratory disease
- Heart failure
- Anaemia
187
How does respiratory disease decrease partial pressure of inspired oxygen?
- Decrease arterial PO2
- So decrease Hb saturation with O2
- So decrease O2 content of the blood
188
How does anaemia decrease partial pressure of inspired oxygen?
- Decreases Hb concentration
| - So decreases O2 content of the blood
189
How does heart failure decrease partial pressure of inspired oxygen?
- Decreases cardiac output
190
The binding of one O2 to Hb increases the affinity of what? for what?
Hb for O2
191
Why is the sigmoid significant?
- Flat upper portions means moderate fall in alveolar Po2 will not affect oxygen loading much
- Steep lower part means peripheral tissues get a lot of oxygen for a small drop in capillary Po2
192
What is the Bohr Effect?
- Decrease in oxygen affinity of haemoglobin
In response to decreased blood pH
- Which results from increased carbon dioxide concentration in the blood
193
How does foetal haemoglobin (HbF) differ from adult haemoglobin?
In the structure
- HbF has 2 ALPHA subunits
- And 2 GAMMA subunits
194
HbF interacts more/less with 2,3-Biphosphoglycerate in red blood cells
less
195
HbF has a higher/lower affinity for O2 compared to adult haemoglobin (HbA)
higher
196
HbF having a higher affinity for O2 than HbA means what?
It would allow O2 to transfer from mother to foetus even if the PO2 is low
197
Myoglobin is present in what muscles?
Skeletal and cardiac muscles
198
How many haem groups are there per myoglobin molecule?
One haem group per myoglobin molecule
199
What is cooperative binding of oxygen?
- Occurs with haemoglobin
| - As oxygen binding increases, the affinity of haemoglobin for more oxygen increases
200
What is increased in haemoglobin caused by?
A conformational or structural change in the haemoglobin molecule
201
Does myoglobin have cooperative binding for O2?
No
202
Myoglobin releases O2 at very high/low PO2
Low
203
What does myoglobin provide for anaerobic conditions
Short-term storage of O2
204
Presence of myoglobin in the blood indicates what?
Muscle damage
205
Oxygen picked up by the blood must be transported in the ______ to the tissues for cellular use
blood
206
CO2 produced at tissues must be transported in the ______ to the lungs for removal from the body
blood
207
What are the three means of CO2 transport in the blood?
- Solution (10%)
- As Bicarbonate (60%)
- As Carbamino Compounds (30%)
208
CO2 in solution follows which law?
Henry's Law
209
Carbon dioxide is how many times more soluble than oxygen?
20 times more soluble
210
What molecule forms Bicarbonate in the blood?
Carbonic Anhydrase
211
Where does the formation of bicarbonate occur?
Occurs in red blood cells
212
Carbamino compounds are formed by what?
Formed by combination of CO2 with terminal amine groups in blood proteins
213
What part of haemoglobin is especially important when forming carbamino-haemoglobin
Globin
214
Formation of carbamino compounds is rapid even without what?
Enzymes
215
Reduced Hb can bind more _____ than _____
CO2 than HbO2
216
What is the Haldane Effect?
Removing O2 from Hb increases the ability of Hb to pick-up CO2 and H+ generated by CO2
217
The Boher effect and the Haldane effect work together to facilitate what?
O2 liberation and uptake of CO2 an H+ generated by CO2 at tissues
218
The Bohr Effect facilitates the removal of O2 from haemoglobin at tissue level by shifting the O2-Hb dissociation curve to what direction?
To the right
219
What effect is occuring when oxygen shifts CO2 dissociation curve to the right?
The Halden Effect
220
What happens to the Hb in the lungs as they pick up O2?
Their ability to bind to CO2 and H+ weakens
221
What is the major rhythm generator in the neural control of respiration?
The medulla
222
Fairly normal ventilation retained if section _____ medulla, ventilation ceases if section ______ medulla
- above
| - below
223
It is now generally believed that the breathing rhythm is generated by a network of neurons called what?
The Pre-Botzinger complex
224
What behavior do the neurons of the Pre-Botzinger complex display?
Pacemaker activity
225
Where are the neurons of the Pre-Botzinger complex located?
Near the upper end of the medullary respiratory centre
226
What gives rise to inspiration?
- Rhythm generated by Pre-Botzinger complex
- Excites Dorsal respiratory group neurones (inspiratory)
- Fire in bursts
- Firing leads to contraction of inspiratory muscles
- When firing stops, passive expiration occurs
227
What happens during "active" expiration during hyperventilation?
- Increased firing of dorsal neurones excites a second group: Ventral respiratory group neurones
Leading to forceful expiration
228
In normal, quiet breathing ventral neurones do not activate what muscles?
Active expiratory muscles
229
The rhythm generated in the medulla can be modified by neurones located where?
In the pons
230
Without the pneumotaxic centre what happens?
Breathing is prolonged inspiratory gasps with brief expiration
231
What is the name that decsribes prolonged inspiratory gasps with brief expiration?
Apneusis
232
What is the apneustic centre for?
Impulses from these neurones excite inspiratory area of the medulla which prolongs inspiration
233
Rhythm can be modified by inputs from what?
Pons
234
Respiratory centres are influenced by stimuli received from what receptors?
- Higher brain centres
- Stretch receptors
- Juxtapulmonary (J) receptors
- Joint receptors
- Baroreceptors
- Central chemoreceptors
- Peripheral chemoreceptors
235
Give three examples of higher brain centres
- Cerebral cortex
- Limbic system
- Hypothalamus
236
What are stretch receptors?
- In the walls of bronchi and bronchioles
| - Cause the inlation Herin-Breur reflex (guard against hyperinflation)
237
What are the Juxtapulmonary (J) receptors?
- Stimulated by pulmonary capillary congestion and pulmonary oedema
- Also stimulated by pulmonary emboli - rapid shallow breathing
238
What are joint receptors stimulated by?
Joint movement
239
What do baroreceptors do?
Increase ventilatory rate in response to decreased blood pressure
240
What receptors relate to the chemical control of respiration?
- Central chemoreceptors
| - Peripheral chemoreceptors
241
What are 4 examples of involuntary modifications of breathing?
- Pulmonary stretch receptors Hering-Breuer Reflex
- Joint Receptors Reflex in Exercise
- Stimulation of repsiratory centre by temperature, adrenalinenor impulses from cerebreal cortex
- Cough reflex
242
What are five factors that may increase ventilation during exercise?
- Reflexes originating from body movement
- Adrenaline release
- Impulses from the cerberal cortex
- Increase in body temperature
- Later: accumulation of CO2 and H+ generated by active muscles
243
Chemical control of respiration is an example of what feedback control system?
Negative Feedback Control System
244
What are the controlled variables in the chemical control of respiration?
-The blood gas tensions (especially carbon dioxide)
245
What receptors sense the values of the gas tensions?
Chemoreceptors
246
What receptors sense tension of oxygen and carbon dioxide (and H+ concentration) in the blood?
Peripheral chemoreceptors
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What does the pneumotaxic centre do to inspiration when stimulated?
Terminates inspiration
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What does the apneustic centre do to inspiration when stimulated?
Excites the inspiratory area of the medulla
249
When are pulmonary stretch receptors activated?
Activated during inspiration
250
What happens when pulmonary stretch receptors are discharged?
Inhibits inspiration
| - Hering-Breuer Reflex
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Do pulmonary stretch receptors switch off during normal respiratory cycle?
Unlikely
- only activated at large >>1litre tidal volumes
- maybe important in newborn babies
- may prevent over-inflation lungs during hard exercise
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What do joint receptors do?
- Impulses from moving limbs reflexly increase breathing
| - Contribute to increased ventilation during exercise
253
Where is the cough reflex receptor located?
Centre in the medulla
254
What is the cough reflex?
- Vital part of body defence mechanisms
| - Helps clear airways of dust, dirt or excessive secretions
255
When is the cough reflex activated?
Activated by irritation of airways or tight airways
256
What does afferent discharge of the cough reflex stimulate?
- Short intake of breath
- Closure of the larynx
- Contraction of abdominal muscles (increases intra-alveolar pressure)
- Opening of the larynx and expulsion of air at high speed
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Where are the central chemoreceptors located?
Near the surface of the medulla of the brainstem
258
What do the chemoreceptors respond to?
H+ concentration of the cerebrospinal fluid (CSF)
259
Cerebrospinal fluid (CSF) is separated fro the blood by what?
Separated by the blood brain barrier
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What is the blood brain barrier impermeable to?
Impermeable to H+ and HCO3-
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What can the blood brain barrier readily diffuse?
Readily diffuses CO2
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CSF contains less ______ than blood and hence is less ______ than blood
- protein
| - buffered
263
What is hypoxia?
Body is deprived of adequate oxygen supply
264
What is hypercapnia
Abnormally elevated carbon dioxide levels in the blood
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When is the hypoxic drive of respiration stimulated?
Stimulated only when arterial Po2 falls to low levels (<8.0 kPa)
266
Hypoxic drive is not important in normal respiration but may become important in patients with what?
- In patients with chronic CO2 retention (eg. patients with COPD)
- Important at high altitudes
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What is hypoxia at high altitudes caused by?
Caused by decreased partial pressure of inspired oxygen (PiO2)
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What are the acute responses to decreased partial pressure of inspired oxygen (PiO2)?
- Hyperventilation
| - Increased cardiac output
269
What are symptoms of acute mountain sickness?
- headache
- fatigue
- nausea
- tachycardia
- dizziness
- sleep disturbance
- exhaustion
- shortness of breath
- unconsciousness
270
What are the chronic adaptations to high altitudes hypoxia?
- Increased RBC production
- Increased 2,3 BPG produced within RBC
- Increased number of capillaries
- Increased number of mitochondria
- Kidneys conserve acid
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What receptor does the effect of the H+ drive of respiration go through?
Peripheral Chemoreceptors
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What molecule does not readily cross the blood brain barrier?
H+
273
What major role do peripheral chemoreceptors play?
Adjusting for acidosis caused by the addition of non-carbonic acid H+ to the blood
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What does the stimulation of the peripheral chemoreceptors by H+ cause?
Causes...
- hyperventilation
- increase in elimination of CO2 from the body (CO2 can generate H+ so its increased elimination help reduce H+ in the body) (important in acid-base balance)
