Physiology Flashcards

(72 cards)

1
Q

What are the four steps of external respiration?

A

Ventilation
Gas exchange between alveoli and blood
Gas transport in the blood
Gas exchange at tissue level

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2
Q

What is ventilation?

A

The mechanical process of moving air between the atmosphere and alveolar sacs

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3
Q

What does Boyle’s law state?

A

As the volume of a gas increases the pressure exerted by the gas decreases
(At a constant temperature)

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4
Q

What two forces hold the thoracic wall and the lungs in close opposition?

A

The intrapleural fluid cohesiveness

The negative intrapleural pressure

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5
Q

How does the intrapleural fluid cohesiveness hold the thoracic wall and the lungs in close opposition?

A

The water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart - this holds the pleural membranes together

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6
Q

How does the negative intrapleural pressure hold the thoracic wall and the lungs in close opposition?

A

The sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and across the chest wall
I.e. the pressure is lowest in the pleural cavity

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7
Q

What three pressures are important in ventilation?

A

Atmospheric pressure
Intra-alveolar pressure
Intrapleural pressure

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8
Q

What does the external intercostal muscle do during inspiration?

A

Contracts to lift the ribs and move out the sternum

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9
Q

How is the volume of the thorax increased vertically during inspiration?

A

Contraction of the diaphragm - this flattens out its dome shape

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10
Q

What does the increase in size of the lungs do to the intra-alveolar pressure?

A

Causes it to drop

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11
Q

What does the drop in intrathoracic pressure during inspiration result in?

A

Air entering the lungs by following a pressure gradient

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12
Q

Is expiration a passive or active process?

A

Passive

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13
Q

How is expiration brought about?

A

Relaxation of inspiratory muscles - the chest wall and stretched lungs recoil to their preinspiratory size because of their elastic properties

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14
Q

What does the recoiling of the lungs do to the intra-alveolar pressure?

A

Causes it to rise

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15
Q

What does the rise in intrathoracic pressure during expiration result in?

A

Air passes out of the lungs by following a pressure gradient

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16
Q

What causes the lungs to recoil during expiration?

A

Elastic connective tissue in the lungs

Alveolar surface tension

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17
Q

What is the alveolar surface tension?

A

The attraction between water molecules at liquid air interface i.e. the walls of the alveoli
This produces a force which resists the stretching of the lungs

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18
Q

What would happen to the alveoli if they were lined with water alone?

A

The surface tension would be too strong and the lung would collapse

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19
Q

What chemical is present to reduce alveolar surface tension?

A

Surfactant

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20
Q

What does the law of Laplace state?

A

The small alveoli i.e. the alveoli with smaller radius have a higher tendency to collapse

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21
Q

How does surfactant reduce the alveolar surface tension and which alveoli does it have more of an effect on?

A

Intersperses between the water molecules lining the alveoli

Lowers the surface tension of smaller alveoli more

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22
Q

What is alveolar interdependence?

A

If an alveolus starts to collapse the surrounding alveoli are stretched, and then recoil: this exerts expanding forces in the collapsing alveolus to open it

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23
Q

What is the tidal volume?

A

The volume of air entering or leaving the lungs in a normal breath (500ml)

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24
Q

What is the inspiratory reserve volume?

A

Extra volume of air which can be inspired over and above the resting tidal volume (3000ml)

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25
What is the inspiratory capacity?
The inspiratory reseve volume and the tidal capacity (3500ml)
26
What is the expiratory reserve volume?
The extra volume of air that can be actively expired beyond the normal tidal volume (1000ml)
27
What is the residual volume?
The minimum volume of air remaining in the lungs even after a maximal expiration (this is to keep them patent) (1200ml)
28
What is the functional residual capacity?
The volume of air in the lungs after normal tidal expiration i.e. residual volume + expiratory reserve volume (2200ml)
29
What is the vital capacity?
The maximum volume of air that can be expired after a maximal inspiration i.e. ERV + TV + IRV (4500ml)
30
What is the total lung capacity?
The maximum volume of air that the lungs can hold (RV + VC) (5700ml)
31
What changes in spirometry will occur in obstructive lung disease?
FVC normal, FEV1 reduced, FEV1/FVC reduced
32
What changes in spirometry will occur in restrictive lung disease?
FVC reduced, FEV1 reduced, FEV1/FVC normal
33
What changes in spirometry will occur in a combination of obstructive and restrictive lung disease?
FVC reduced, FEV1 reduced, FEV1/FVC reduced
34
What is pulmonary compliance?
The measure of effort that has to go into stretching or distending the lungs
35
What factors decrease pulmonary compliance?
``` Pulmonary fibrosis Pulmonary oedema Lung collapse Pneumonia Absence of surfactant ```
36
Why does decreased pulmonary compliance result in shortness of breath?
A greater change in pressure is needed to produce a given change in volume - the lungs are stiffer
37
When might pulmonary compliance become abnormally increased?
If the elastic recoil of the lungs is lost e.g. in emphysema
38
What is anatomical dead space?
The inspired air that remains in the airways and is not available for gas exchange
39
How can pulmonary ventilation be calculated?
Tidal volume x respiratory rate
40
Why is alveolar ventilation less than pulmonary ventilation?
Because of the presence of anatomical dead space
41
How can alveolar ventilation be calculated?
(Tidal volume - dead space) x respiratory rate
42
What is the definition of pulmonary ventilation?
The volume of air breathed out and in per minute
43
What is the definition of alveolar ventilation?
The volume of air exchanged between the atmosphere and alveoli per minute
44
To increase pulmonary ventilation, what is the most useful thing to do and why?
Increase the depth of breathing because of dead space
45
What is the definition of perfusion?
The rate at which blood is passing through the lungs
46
What is the V/Q ratio at the bottom of the lung?
Blood flow > ventilation
47
What is the V/Q ratio at the top of the lung?
Ventilation > blood flow
48
What is alveolar dead space?
Ventilated alveoli which are not adequately perfused with blood
49
What is the physiological dead space?
The anatomical dead space + the alveolar dead space
50
What physiological response does an increase of CO2 in an alveoli (due to increased perfusion) trigger?
Relaxation of airway smooth muscle Dilation of local airways This decreases airway resistance which results in increased airflow to the affected alveoli
51
What physiological response does a decrease in O2 in an alveoli (due to decreased ventilation) trigger?
Contraction of local pulmonary arteriolar smooth muscle Constriction of local blood vessels Increased vascular resistance Decreased blood flow
52
Why would an increase in O2 in an alveoli result in increased local pulmonary blood flow?
To balance up the V/Q mismatch that has occurred and to oxygenate as much blood as possible
53
What is the diffusion coefficient of a gas?
The solubility of the gas in membranes
54
How is most oxygen transported in the blood?
Bound to haemoglobin
55
In what two forms is oxygen present in blood?
Dissolved in blood | Bound to haemoglobin
56
What might shift the oxygen-haemoglobin dissociation curve to the right?
An increase in PCO An increase in [H+] An increase in temperature An increase in 2,3-bisphosphoglycerate
57
What shape is the oxygen-haemoglobin dissociation curve?
Sigmoid
58
What shape is the oxygen-myoglobin dissociation curve?
Hyperbolic
59
How is CO2 transported in the blood?
In solution As bicarbonate - main form of transport As carbamino compounds
60
Where does the formation of bicarbonate in the blood take place?
Red blood cells
61
What enzyme facilitates the formation of bicarbonate in blood?
Carbonic anhydrase
62
How are carbamino compounds formed?
Combination of CO2 with terminal amine groups in blood proteins
63
Where is the breathing rhythm generated?
A network of neurones called the pre-botzinger complex
64
Where is the pre-botzinger complex generated?
The upper end of the medullary respiratory centre
65
Where is the impulse for inspiration generated?
The dorsal group of neurones in the medulla
66
What happens during hyperventilation when there is increased firing from the dorsal group of neurones?
The ventral respiratory group neurones are activated which excite internal intercostal muscles, abdominal muscles etc.
67
What is the pneumotaxic centre?
An area in the pons which can modify the respiratory rhythm generated in the medulla
68
What does stimulation of the pneumotaxic centre do?
Terminates inspiration
69
What is the apneustic centre?
An area in the pons which can modify the respiratory rhythm generated by the medulla
70
What does stimulation of the apneustic centre do??
Prolongs inspiration
71
When are pulmonary stretch receptors activated and what is this reflex called?
During inspiration | Hering-Breuer reflex
72
How does joint movement modify breathing?
Impulses from moving limbs reflexively increase breathing