Physiology

Question 1

What are the four steps of external respiration?

Answer 1

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

Question 2

What is ventilation?

Answer 2

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

Question 3

What does Boyle’s law state?

Answer 3

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

Question 4

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

Answer 4

The intrapleural fluid cohesiveness

The negative intrapleural pressure

Question 5

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

Answer 5

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

Question 6

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

Answer 6

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

Question 7

What three pressures are important in ventilation?

Answer 7

Atmospheric pressure
Intra-alveolar pressure
Intrapleural pressure

Question 8

What does the external intercostal muscle do during inspiration?

Answer 8

Contracts to lift the ribs and move out the sternum

Question 9

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

Answer 9

Contraction of the diaphragm - this flattens out its dome shape

Question 10

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

Answer 10

Causes it to drop

Question 11

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

Answer 11

Air entering the lungs by following a pressure gradient

Question 12

Is expiration a passive or active process?

Answer 12

Passive

Question 13

How is expiration brought about?

Answer 13

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

Question 14

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

Answer 14

Causes it to rise

Question 15

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

Answer 15

Air passes out of the lungs by following a pressure gradient

Question 16

What causes the lungs to recoil during expiration?

Answer 16

Elastic connective tissue in the lungs

Alveolar surface tension

Question 17

What is the alveolar surface tension?

Answer 17

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

Question 18

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

Answer 18

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

Question 19

What chemical is present to reduce alveolar surface tension?

Answer 19

Surfactant

Question 20

What does the law of Laplace state?

Answer 20

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

Question 21

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

Answer 21

Intersperses between the water molecules lining the alveoli

Lowers the surface tension of smaller alveoli more

Question 22

What is alveolar interdependence?

Answer 22

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

Question 23

What is the tidal volume?

Answer 23

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

Question 24

What is the inspiratory reserve volume?

Answer 24

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

Question 25

What is the inspiratory capacity?

Answer 25

The inspiratory reseve volume and the tidal capacity (3500ml)

Question 26

What is the expiratory reserve volume?

Answer 26

The extra volume of air that can be actively expired beyond the normal tidal volume (1000ml)

Question 27

What is the residual volume?

Answer 27

The minimum volume of air remaining in the lungs even after a maximal expiration (this is to keep them patent) (1200ml)

Question 28

What is the functional residual capacity?

Answer 28

The volume of air in the lungs after normal tidal expiration i.e. residual volume + expiratory reserve volume (2200ml)

Question 29

What is the vital capacity?

Answer 29

The maximum volume of air that can be expired after a maximal inspiration i.e. ERV + TV + IRV (4500ml)

Question 30

What is the total lung capacity?

Answer 30

The maximum volume of air that the lungs can hold (RV + VC) (5700ml)

Question 31

What changes in spirometry will occur in obstructive lung disease?

Answer 31

FVC normal, FEV1 reduced, FEV1/FVC reduced

Question 32

What changes in spirometry will occur in restrictive lung disease?

Answer 32

FVC reduced, FEV1 reduced, FEV1/FVC normal

Question 33

What changes in spirometry will occur in a combination of obstructive and restrictive lung disease?

Answer 33

FVC reduced, FEV1 reduced, FEV1/FVC reduced

Question 34

What is pulmonary compliance?

Answer 34

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

Question 35

What factors decrease pulmonary compliance?

Answer 35

``` Pulmonary fibrosis Pulmonary oedema Lung collapse Pneumonia Absence of surfactant ```

Question 36

Why does decreased pulmonary compliance result in shortness of breath?

Answer 36

A greater change in pressure is needed to produce a given change in volume - the lungs are stiffer

Question 37

When might pulmonary compliance become abnormally increased?

Answer 37

If the elastic recoil of the lungs is lost e.g. in emphysema

Question 38

What is anatomical dead space?

Answer 38

The inspired air that remains in the airways and is not available for gas exchange

Question 39

How can pulmonary ventilation be calculated?

Answer 39

Tidal volume x respiratory rate

Question 40

Why is alveolar ventilation less than pulmonary ventilation?

Answer 40

Because of the presence of anatomical dead space

Question 41

How can alveolar ventilation be calculated?

Answer 41

(Tidal volume - dead space) x respiratory rate

Question 42

What is the definition of pulmonary ventilation?

Answer 42

The volume of air breathed out and in per minute

Question 43

What is the definition of alveolar ventilation?

Answer 43

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

Question 44

To increase pulmonary ventilation, what is the most useful thing to do and why?

Answer 44

Increase the depth of breathing because of dead space

Question 45

What is the definition of perfusion?

Answer 45

The rate at which blood is passing through the lungs

Question 46

What is the V/Q ratio at the bottom of the lung?

Answer 46

Blood flow > ventilation

Question 47

What is the V/Q ratio at the top of the lung?

Answer 47

Ventilation > blood flow

Question 48

What is alveolar dead space?

Answer 48

Ventilated alveoli which are not adequately perfused with blood

Question 49

What is the physiological dead space?

Answer 49

The anatomical dead space + the alveolar dead space

Question 50

What physiological response does an increase of CO2 in an alveoli (due to increased perfusion) trigger?

Answer 50

Relaxation of airway smooth muscle Dilation of local airways This decreases airway resistance which results in increased airflow to the affected alveoli

Question 51

What physiological response does a decrease in O2 in an alveoli (due to decreased ventilation) trigger?

Answer 51

Contraction of local pulmonary arteriolar smooth muscle Constriction of local blood vessels Increased vascular resistance Decreased blood flow

Question 52

Why would an increase in O2 in an alveoli result in increased local pulmonary blood flow?

Answer 52

To balance up the V/Q mismatch that has occurred and to oxygenate as much blood as possible

Question 53

What is the diffusion coefficient of a gas?

Answer 53

The solubility of the gas in membranes

Question 54

How is most oxygen transported in the blood?

Answer 54

Bound to haemoglobin

Question 55

In what two forms is oxygen present in blood?

Answer 55

Dissolved in blood | Bound to haemoglobin

Question 56

What might shift the oxygen-haemoglobin dissociation curve to the right?

Answer 56

An increase in PCO An increase in [H+] An increase in temperature An increase in 2,3-bisphosphoglycerate

Question 57

What shape is the oxygen-haemoglobin dissociation curve?

Answer 57

Sigmoid

Question 58

What shape is the oxygen-myoglobin dissociation curve?

Answer 58

Hyperbolic

Question 59

How is CO2 transported in the blood?

Answer 59

In solution As bicarbonate - main form of transport As carbamino compounds

Question 60

Where does the formation of bicarbonate in the blood take place?

Answer 60

Red blood cells

Question 61

What enzyme facilitates the formation of bicarbonate in blood?

Answer 61

Carbonic anhydrase

Question 62

How are carbamino compounds formed?

Answer 62

Combination of CO2 with terminal amine groups in blood proteins

Question 63

Where is the breathing rhythm generated?

Answer 63

A network of neurones called the pre-botzinger complex

Question 64

Where is the pre-botzinger complex generated?

Answer 64

The upper end of the medullary respiratory centre

Question 65

Where is the impulse for inspiration generated?

Answer 65

The dorsal group of neurones in the medulla

Question 66

What happens during hyperventilation when there is increased firing from the dorsal group of neurones?

Answer 66

The ventral respiratory group neurones are activated which excite internal intercostal muscles, abdominal muscles etc.

Question 67

What is the pneumotaxic centre?

Answer 67

An area in the pons which can modify the respiratory rhythm generated in the medulla

Question 68

What does stimulation of the pneumotaxic centre do?

Answer 68

Terminates inspiration

Question 69

What is the apneustic centre?

Answer 69

An area in the pons which can modify the respiratory rhythm generated by the medulla

Question 70

What does stimulation of the apneustic centre do??

Answer 70

Prolongs inspiration

Question 71

When are pulmonary stretch receptors activated and what is this reflex called?

Answer 71

During inspiration | Hering-Breuer reflex

Question 72

How does joint movement modify breathing?

Answer 72

Impulses from moving limbs reflexively increase breathing