Anatomy of Chest Wall and Mechanics of Breathing Flashcards
Which gas law is breathing based on?
Boyle’s Law
What does Boyle’s Law state?
The pressure exerted by a gas is inversely proportional to its volume
What is the top of the lung called?
Apex
What is the first lobe below the apex called in both lungs
Superior lobe
What is different in the superior lobe of the left lung compared to the right
- Much bigger - Curved lower border
What are the lungs and interior of the thorax covered in?
Pleural sac
What is the pleural membrane made of?
An extremely thin layer of intrapleural fluid
What does the visceral pleural membrane coat?
Outer surface of the lungs
What does the parietal pleural membrane coat?
Inner surface of the ribs
What does the interaction between the pleural membranes mean for the lungs and the ribs?
The lungs are effectively stuck to the ribs
What is pleurisy?
Inflammation of the pleura
Why does breathing occur?
Thoracic cavity changes volume
Why do the lungs need to be “stuck” to the ribs?
- The lungs are trying to move in the way and would collapse
- The ribs are moving against this force to maintain the shape of the cavity
Where do the two pleural membranes overlap?
The hilux of the lung
What is the overlapping membrane known as?
Visceralparietal membrane
What volume of fluid is there in the pleural cavity?
3ml
What does the pleural fluid allow the membranes to do?
- Slide over eachother
- Stick to eachother strongly (imagine 2 microscope slides with water between them
What symptoms, to do with the pleural membranes, can you get when you have pleurisy?
Pain and discomfort as they can’t slide over each other
What is the average negative pressure of the lungs due to the interaction with the ribs?
-3mm Hg
What is the name given to the force that the lungs and the ribs exert on each other due to the pleural membranes?
Elastic recoil
What is pneumothorax?
A collapse of the lung due to loss of pleural membrane interaction
What happens to the ribcage as the diaphragm is relaxed?
It rises
What effect does the rising of the ribcage have on the thoracic cavity and what does this cause?
- Lowers the pressure
- Air from the atmosphere moves into the lungs
What happens to the thoracic pressure when the air moves in?
- Increases above atmospheric pressure (PATM)
What happens to the alveoli when air moves into them?
- They expand
- Elastic fibres stretch
How does air move back out of the alveoli?
Under elastic recoil from the elastic fibres surrounding the alveolar sacs
What two groups of muscles can be recruited to aid in expiration during exercise?
- Intercostal muscles
- Abdominal muscles
How do the intercostal muscles aid in expiration?
- Innervating alpha motor neurone is switched off and they relax
How do the abdominal muscles increase expiration?
- Contraction of them increases thoracic pressure by decreasing thoracic volume
What shape is the diaphragm when it contracts?
- Flat
What does the shape change to a flat shape of the diaphragm do to thoracic pressure?
- Increases volume so decreases pressure
How does intercostal muscle contraction increase anterior posterior thoracic volume?
Similar to a pump handle
How does intercostal muscle contracting increase lateral thoracic volume?
Similar to a bucket handle shape
How does inspiration follow Boyle’s Law?
Air moves in from the atmosphere from high pressure to low pressure because the volume of the container (lungs) is increased.
How does expiration follow Boyle’s Law?
Pressure of the thoracic cavity excedes atmospheric pressure as the volume is reduced by elastic recoil, rib cage decending and diaphragm rising
List reasons why intrapleural pressure is always lower than alveolar pressure
- Alveoli have residual volume in them ALL THE TIME
- Intrapleural space contains fluid
- Intrapleural pressure is always negative compared to atmospheric pressure, whereas alveolar pressure is sometimes above
- If intrapleural pressure equals alveolar pressure then a pneumothorax will form
