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Flashcards in Physiology Deck (72):
1

What are the four steps of external respiration?

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

2

What is ventilation?

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

3

What does Boyle's law state?

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

4

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

The intrapleural fluid cohesiveness
The negative intrapleural pressure

5

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

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

6

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

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

7

What three pressures are important in ventilation?

Atmospheric pressure
Intra-alveolar pressure
Intrapleural pressure

8

What does the external intercostal muscle do during inspiration?

Contracts to lift the ribs and move out the sternum

9

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

Contraction of the diaphragm - this flattens out its dome shape

10

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

Causes it to drop

11

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

Air entering the lungs by following a pressure gradient

12

Is expiration a passive or active process?

Passive

13

How is expiration brought about?

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

14

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

Causes it to rise

15

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

Air passes out of the lungs by following a pressure gradient

16

What causes the lungs to recoil during expiration?

Elastic connective tissue in the lungs
Alveolar surface tension

17

What is the alveolar surface tension?

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

18

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

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

19

What chemical is present to reduce alveolar surface tension?

Surfactant

20

What does the law of Laplace state?

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

21

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

Intersperses between the water molecules lining the alveoli
Lowers the surface tension of smaller alveoli more

22

What is alveolar interdependence?

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

23

What is the tidal volume?

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

24

What is the inspiratory reserve volume?

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

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