Respiratory Physiology 2.2-mechanisms of breathing Flashcards
What is Boyle’s law?
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.
What is Dalton’s law?
Dalton’s Law states that the total pressure of a gas mixture is the sum of the pressures of the individual gases.
What is Charles Law?
Charles Law states that the volume occupied by a gas is directly related to the absolute temperature (v a T)
What is Henry’s Law?
Henry’s Law states that the amount of gas dissolved in a liquid is determined by the pressure of the gas and it’s solubility in the liquid
How does breathing happen?
thoracic cavity changes volume
What does Boyle’s law mean?
increased volume leads to decreased pressure
decreased volume leads to increased pressure
Gases always move from high pressure to low pressure
What muscles does inspiration use?
The muscles of inspiration include the diaphragm, external intercostals, (and under heavy respiratory load) sternocleidomastoids and scalenes
What muscles does expiration use when we want to forcibly expire?
internal intercostal and abdominal muscles
What does the diaphragm separate?
abdominal and thoracic cavity
Where are the internal and external intercostal muscles?
muscles that run between the ribs
How do the sternocleidomastoids and scalenes move?
act on upper ribs and clavicle to lift them up for expansion of chest wall
What are the muscles of expiration?
the internal intercostal muscles and the abdominal muscles
Where are external and internal intercostal muscles in relation to one another?
internal intercostal muscles run in opposite direction underneath the external intercostal muscles
What happens when internal intercostal muscles contract?
pull ribcage downwards and inwards
What cavity do the abdominal act on when they contract?
abdominal cavity and reduce volume
How is expiration brought about?
organs get pushed up against the diaphragm.
And then diaphragm gets pushed up into the thoracic cavity (by pushing diaphragm upwards) and we decrease the volume of the thoracic cavity.
How do we inspire?
Diaphragm contracts, increasing superior and inferior dimensions of the lungs.
The phrenic nerve innervates the diaphragm and it causes the diaphragm to contract.
When the diaphragm contracts it flattens down.
So by flattening down, we end up increasing the volume of the thoracic cavity.
If we increase the volume of the thoracic cavity, we decrease the pressure.
If decrease pressure below atmospheric pressure- air flows from high pressure to low pressure.
How do we expire?
phrenic nerve stops innervating the diaphragm and the diaphragm stops contracting and relaxes to dome shape.
And thoracic cavity volume is reduced and increases pressure to above atmospheric pressure.
And air leaves lungs.
Mechanisms of the exterior intercostals?
through action on the sternum ‘pump handle’ - increase volume of thoracic cavity in the anterior and posterior dimensions
through actions on ribs ‘bucket handle’- increase in volume of thoracic cavity in the lateral dimensions
What happens when internal intercostal muscles are employed?
actively pull the ribcage down and the sternum in
Summary of the mechanics of breathing?
Inspiration: airways are pulled open by physical forces of inspiration - less resistance.
Expiration: airways are compressed by physical forces of expiration
What happens during asthma?
Inappropriate constriction of the bronchial smooth muscle- which narrows the airways and increases resistance.
Aggravated during expiration because those airways are being compressed anyway
What is Intra-thoracic (Alveolar) pressure?
pressure inside the thoracic cavity (pressure inside lungs)
May be negative or positive relative to the atmospheric pressure.
What is a positive and negative pressure?
positive- more than atmospheric pressure
negative- less than atmospheric pressure
What is intra-pleural pressure?
the pressure inside the pleural cavity, typically negative compared to atmospheric pressure (in healthy lungs)
What is transpulmonary pressure?
difference between alveolar pressure and intra-pleural pressure.
Transpulmonary pressure should always be positive because intrapleural pressure should always be negative.
Pt= Palv-Pip
Describe alveolar pressure throughout the inspiratory phase and expiratory phase ?
inspiratory phase- the pressure inside lungs is always less than the atmospheric pressure
expiratory phase- the pressure inside lungs is greater than atmospheric pressure and air moves out of the lungs
What happens when alveolar pressure is the same as atmospheric pressure?
get no movement of air
What happens to intrapleural pressure during expiration and inspiration?
negative throughout breathing cycle
inspiration- intrapleural pressure becomes more negative- chest wall leading the expansion of the thoracic cavity (pulls parietal pleura from visceral) and decrease pressure
expiration- becomes less negative. as chest wall contracting as its following the elastic recoil of the lungs and the two get compressed
