anatomy of chest wall and breathing mechanics

Question 1

Describe how the muscles of respiration act to inc and dec thoracic volume:

Answer 1

Boyles law: pressure exerted by gas is inverse to volume. Therefore an increase in volume leads to a decrease in pressure.

The muscles of inspiration are – the diaphragm, external intercostals, sternocleidomastoid and scalenes.

The muscles of expiration are – the internal intercostals and abdominals

Expiration is passive at rest however these muscles are utilised in severe respiratory load.

As the diaphragm contracts it moves down which increases the thoracic volume which leads to a drop in pressure which pulls air into the lungs

Question 2

describe what the parietal and visceral pleura does:

Answer 2

Visceral pleural membrane – coats outer surface of the lungs

Parietal pleural membrane – coats the inner surface of ribs

The parietal pleura is sensitive to pain, temperature and pressure however the visceral pleura is not

Question 3

Relate Boyle’s law to the mechanics of breathing:

Answer 3

Boyle’s law states in a closed space, the pressure exerted by a gas is inversely proportional to its volume

Therefore an increase in volume leads to a decrease in pressure and a decrease in volume leads to an increase in pressure

Question 4

Explain why intrapleural pressure is always less than alveolar pressure:

Answer 4

The pleural cavity is always lined by a thin layer of fluid that’s secreted by the visceral layer of the pleura.

This fluid is constantly pumped from the pleural cavity into lymphatic vessels.

The pumping of fluid creates the negative pressure in the pleural cavity.

This keeps the lungs always inflated.