RESPIRATION PHYSIOLOGY

Question 1

Define ventilation.

Answer 1

The mechanical process of gas exchange between the atmosphere and the alveoli of the lungs.

Question 2

Describe gas exchange between alveoli and blood.

Answer 2

exchange of CO2 and O2 between alveoli and the blood in pulmonary capillaries.

Question 3

Describe gas transport in the blood.

Answer 3

Binding and transport of O2 and CO2 between the lungs and tissues via circulating blood.

Question 4

Describe gas exchange at tissue level.

Answer 4

The exchange of O2 and CO2 between blood in systemic capillaries and the tissues/body cells.

Question 5

Define Boyle’s Law.

Answer 5

Boyle’s Law states that at any constant temperature, as the volume of a gas increases, the pressure exerted by the gas decreases and vice versa.

Question 6

Define atmospheric pressure.

Answer 6

Pressure exerted by the weight of the gas in the atmosphere on objects on the earth’s surface (760mmHg at sea level).

Question 7

Define intra-alveolar pressure.

Answer 7

The pressure within the alveoli (760mmHg when in equilibrium with atmospheric pressure).

Question 8

Define intra-pleural pressure.

Answer 8

The pressure within the pleural sac, i.e. the pressure exerted outside the lungs but within the thoracic cavity (usually less than atmospheric, typically 756mmHg).

Question 9

Describe intrapleural fluid cohesiveness.

Answer 9

One of the forces which holds the thoracic wall and lungs in close opposition. Water molecules in intrapleural fluid resist being pulled apart, accounting for the pleural membranes tendency to stick together.

Question 10

Describe negative intrapleural pressure.

Answer 10

The sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung and chest walls, forcing the lungs to expand outwards and the chest to squeeze inwards.

Question 11

Transmural pressure gradient.

Answer 11

LUNGS: alveolar pressure pushes outwards, intrapleural pressure pushes inward. Pressure difference creates transmural pressure gradient that pushes on the lungs, stretching them to fill the larger thoracic cavity.

Across thoracic wall, atmospheric pressure pushes inward and intrapleural pressure pushes outwards. Pressure difference creates a transmural pressure gradient that pushes inward and compresses the thoracic wall.

Question 12

Process of inspiration.

Answer 12

Active process, depending on the contraction of inspiratory muscles, in which air flows from high-pressure regions to low pressure regions down a pressure gradient.

Question 13

Describe the intra-alveolar pressure before inspiration.

Answer 13

Intra-alveolar pressure is equivalent to atmospheric pressure before inspiration.

Question 14

What must happen to intra-alveolar pressure in order for air to flow into the lungs during inspiration?

Answer 14

Intra-alveolar pressure must become less than atmospheric pressure.

Question 15

During inspiration, the thorax and lungs expand as a result of what?

Answer 15

Contraction of inspiratory muscles. External intercostal muscle contraction lifts the ribs and moves out the sternum (bucket-handle mechanism). Movement of ribs results in a change of the anteroposterior diameter of the thorax.

Question 16

How is thorax volume increased vertically?

Answer 16

Contraction of the diaphragm - flattening out its dome shape, innervated by C3, 4, 5 of the phrenic nerve.

Question 17

How does intra-alveolar pressure become equal to atmospheric pressure?

Answer 17

Increased size of lungs causes intra-alveolar pressure to fall as air molecules become contained in larger volume (Boyle’s Law). Air then enters lungs down a pressure gradient, until intra-alveolar pressure becomes equal to atmospheric pressure.

Question 18

How are the airways pulled open during inspiration?

Answer 18

Expanding thorax and falling intrapleural pressure.

Question 19

Define normal expiration.

Answer 19

Passive process caused by relaxation of inspiratory muscles.

Question 20

What property enables chest wall and stretched lungs to recoil to their pre-inspiratory size?

Answer 20

elastic connective tissue

Question 21

What does recoil of the lungs cause?

Answer 21

Increase in intra-alveolar pressure, as air molecules are contained in a smaller volume.

Question 22

What happens to intrapleural pressure during expiration?

Answer 22

Intrapleural pressure increases.

Question 23

Define dynamic airway compression.

Answer 23

The compression of the alveoli and airways by rising pleural pressure during active expiration. Makes active expiration difficult in patients with airway obstruction.

Question 24

Pressure applied to alveoli aids in what?

Answer 24

Expelling air from the lungs.

Question 25

What is alveolar surface tension?

Answer 25

Attraction between water molecules resisting stretching of the lungs.

Question 26

Describe the Law of Laplace.

Answer 26

Alveoli with a smaller radius, r, have a higher tendency to collapse.

Question 27

What is pulmonary surfactant?

Answer 27

Complex mixture of lipids and proteins secreted by type II alveoli, lowering alveolar surface tension by interspersing between water molecules.

Question 28

What does pulmonary surfactant prevent in smaller alveoli?

Answer 28

Lowers their surface tension, preventing them from collapsing and emptying their contents into larger alveoli.

Question 29

Describe alveolar interdependence.

Answer 29

Helps to keep alveoli open, by stretching and recoiling surrounding alveoli if an alveolus starts to collapse. Thus exerting expanding forces on the collapsing alveolus to open it.

Question 30

What forces keep the alveoli open?

Answer 30

Transmural pressure gradient, pulmonary surfactant and alveolar interdependence.

Question 31

What forces promote alveolar collapse?

Answer 31

Elasticity of stretched pulmonary connective tissue fibres and alveolar surface tension.

Question 32

What effect does pneumothorax have on transmural pressure gradient?

Answer 32

Abolishes it.