Lecture 2

Question 1

Define Boyle’s Law

Answer 1

Pressure exerted by a gas is inversely proportional to its volume

Question 2

What is the pleural cavity?

Answer 2

The pleura is a double layer of serous membrane that surrounds each lung. The space between these two membranes is the pleural cavity and is filled with 3ml of fluid.

Question 3

Name the two membranes of the pleura

Answer 3

Visceral pleural membrane - coats the outer surface of the lungs
Parietal pleural membrane - coats the inner surface of the ribs

Question 4

Describe the three relevant pressures in the thoracic cavity

Answer 4

Intra-thoracic pressure - pressure inside the lungs and can be positive or negative
Intra-pleural pressure - pressure inside the pleural cavity and should always be negative
Transpulmonary pressure - this is the difference between the alveolar pressure and the intra-pleural pressure and should always be positive

Question 5

What is the biggest muscle of expiration?

Answer 5

The diaphragm

Question 6

What are the mechanics of inspiration?

Answer 6

The external intercostal muscles pull the rib cage outwards and upwards and the diaphragm moves downwards to increase volume of the lungs and draw air in.

Question 7

What are the mechanics of expiration?

Answer 7

The intercostal muscles and the diaphragm relax and air is forced out the lungs. Most of the time this is a passive process but abdominal muscles can be used to do this faster. They contract and force the contents of the abdominal cavity up pushing on the thoracic cavity, making it smaller, increasing the pressure and forcing air out.