Anatomy of the Chest Wall and the mechanisms of Breathing Flashcards
Boyle’s Law
states that the pressure exerted by a gas is inversely proportional to to its volume (P a 1/V).
Note that gases (singly or in mixtures) move from areas of high pressure to areas of low pressure
How much fluid is in the pleural sac
5ml of pleural fluid
What is the function of the pleural fluid
Acts as a lubricant to allow the lungs to glide across the ribs and the friction caused by this causes the membranes resist separation meaning that when the ribs expand so do the lungs
Describe what happens to the relationship between the lungs and pleural membranes when a pneumothorax occurs
Air flows in-between the membranes causing the lung to collapse to its unstreched size
Describe the mechanism of breathing
Breathing occurs because the thoracic cavity changes volume, based on Boyles Law increasing the volume of gas decreases the pressure and vice versa. Gases always move from high pressure to low pressure.
When we inhale the volume of gas in lungs increases=low pressure so the gas inside leaves to the atmosphere when we exhale. This leaves the lungs with high pressure as there is low volume, so we inhale. This alternates to allow breathing to occur.
Which muscles are used when we breathe?
Inspiration uses external intercostals muscles and the diaphragm.
Expiration is passive at rest, but uses internal intercostal and abdominal muscles during severe respiratory load.
What does the contraction of the external intercostal muscles do?
The external intercostals increase the anterior, posterior and lateral dimensions
Describe the action of the diaphragm during breathing?
Relaxed during expiration - in its domed shape
Contracts during inspiration - increases the thoracic volume, the muscle moves inferiorly
Describe the movement of the ribs and sternum during inspiration
Pump handle motion increases anterior and posterior movement
Bucket handle motion increases lateral dimension of the ribs
Intra-thoracic (Alveolar) Pressure (PA):
pressure inside the thoracic cavity, (essentially pressure inside the lungs). May be negative or positive compared to atmospheric pressure.
Intra-pleural Pressure (Pip):
pressure inside the pleural cavity, ALWAYS negative (in healthy lungs at least!)
Transpulmonary pressure (PT):
difference between alveolar pressure and intra-pleural pressure. ALWAYS positive (in health) because Pip is always negative. PT = PA – Pip.
What is the bulk flow of air proportional to?
Bulk flow of air between the atmosphere and alveoli is proportional to the difference between the atmospheric and alveolar pressures and inversely proportional to the airway resistance: F = (Patm- PA)/R
Describe the importance of the relationship between the pleural membranes and the importance of lung inflation.
Lungs are essentially stuck to the ribcage and diaphragm due to the relationship of the pleural membrane
Meaning when the rib cage moves the lungs follow
allows air to flow into the lungs and create harmony when breathing
Explain why the intrapleural pressure is always negative
as the ribs and lungs are constantly trying to pull apart but fail to do so due to the pleural fluid. (increases volume decreases pressure )
