Overview Of Respiration and Respiratory Mechanics

Question 1

Explain internal respiration

Answer 1

Internal respiration refers to the intracellular mechanisms which consume O2 and CO2

Question 2

Explain external respiration

Answer 2

External respiration is the sequence of events leading to exchange of CO2 and O2 between the external environment and the cells of the body

Question 3

What are the 4 steps of external respiration

Answer 3

1. Ventilation
2. Gas exchange between alveoli and blood
3. Gas transport in the blood
4. Gas exchange at the tissue level

Question 4

Explain ventilation - first step of external respiration

Answer 4

Ventilation is the process of moving air between the atmosphere and alveolar sacs

Question 5

Describe the opposing forces acting on the lungs

Answer 5

Forces keeping the alveoli open:

• transmural pressure gradient
• pulmonary surfactant
• alveolar independence

Elastic forces promoting alveolar collapse:

• elastic recoil of lungs and chest wall
• alveolar surface tension

Question 6

Explain how the lungs adhere to the chest wall and follow its movement

Answer 6

1. Transmural pressure gradient: the sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and across the chest wall
2. The intrapleural fluid cohesiveness: the water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart. Hence the pleural membranes tend to stick together.

Question 7

Explain the respiratory mechanisms and the relationship between atmospheric, intra-alveolar and intra-pleural pressures

Answer 7

Atmospheric pressure - pressure caused by weight of gas in atmosphere on earths surface. 760mmHg

Intra-alveolar pressure - pressure within the lung alveoli. 760mmHg

Intrapleural pressure - pressure exerted outside the lungs within the pleural cavity. Usually less than atmospheric pressure

Question 8

Explain the significance of transmural pressure gradient across the lung wall and across the chest wall

Answer 8

Transmural pressure gradient is essential for the expansion of the lungs

Question 9

Explain what happens to the pressure during a pneumothorax

Answer 9

Pneumothorax - air in pleural space.

Can abolish transmural pressure gradient (by raising intrathoracic pressure) leading to lung collapse

Question 10

Explain Boyle’s Law

Answer 10

At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas

As the volume of a gas increases the pressure exerted by the gas decreases

Question 11

Processes of inspiration and expiration

Answer 11

Inspiration is an active process brought about by contraction of inspiratory muscles

Normal expiration is a passive process bought about by relaxation of inspiratory muscles

Question 12

Which inspiratory muscles are used during normal resting breathing

Answer 12

The diaphragm is the major inspiratory muscle and increases the volume of the thorax vertically on contraction

The external intercostal muscle contraction lifts the ribs and moves out the sternum

Question 13

How do the lungs recoil

Answer 13

Elastic connective tissue in the lungs helps the structure bounce into shape

Alveolar surface tension is attraction between water molecules at liquid air interface and produces a force which resists the stretching of the lungs

Question 14

What is the role and importance of pulmonary surfactant

Answer 14

According to the law of LaPlace: smaller alveolar have a higher tendency to collapse

Pulmonary surfactant lowers alveolar surface tension by interspersing between the water molecules lining the alveoli

Question 15

Explain alveolar independence

Answer 15

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