Respiratory: Physiology of Breathing L14 Flashcards
Explain the three main components in the respiratory system.
External respiratory system: where the exchange of oxygen and carbon dioxide occurs between the atmosphere and pulmonary blood flow.
Transport: where the oxygen travels in the blood towards the tissues and carbon dioxide flows away.
Internal respiratory system: gas exchange occurs between systemic capillaries and tissues. Also includes uses of gases in cellular respiration.
Explain the 5 steps of respiration.
Ventilation: air moving in and out of lungs to supply alveoli with fresh oxygen and remove carbon dioxide. This is an example of bulk flow.
Gas exchange across the alveolar membrane: oxygen and carbon dioxide move down their pressure gradients into or out of the alveoli. This is an example of diffusion.
Gas Transport: oxygen rich blood travels away from the lung and towards the heart, which then pumps it to systemic tissues. This is an example of bulk flow.
Gas exchange across capillary membranes: oxygen and carbon dioxide move down their pressure gradients into or out of the capillaries. This is an example of diffusion.
Cellular respiration: cells in systemic tissues use up oxygen and produce carbon dioxide.
Explain Boyle’s Law and how this relates to gas movements.
P1V1 = P2V2. This means at a constant temperature, the volume of gas in inversely related to pressure: when volume increases, pressure decreases. If pressure is exerted on a gas it decreases in volume.
When we inspire, the volume in our lungs increase, so that pressure in alveoli is lower than pressure of atmosphere. Gas flows in leading to pressure equalisation.
Explain the Law of Partial Pressures.
Px=Fx x Pa. The partial pressure of a gas is the amount of pressure that gas exerts individually in relation to total pressure exerted by all gases.
Partial pressure is equal to the percentage or fraction of a mixture composed of a gas (e.g the percentage of oxygen in the atmosphere) multiplied by the total pressure of that mixture (in the case of the atmosphere, this is barometric pressure).
Explain Dalton’s Law.
Barometric Pressure = sum of partial pressures of all the gases in a mixture.
Dalton’s law states that the total pressure of a mixture is equal to the sum of the partial pressures of the gases in that mixture.
In the atmosphere, barometric pressure = pressure of oxygen, carbon dioxide and nitrogen. Equates to approx 760mmHg (at sea level).
What is the pressure of oxygen in the atmosphere? Calculate using the ‘Law of partial pressures’.
PO2 = FO2 x PB
PO2 = 21% x 760
=159mmHg
What is the pressure of carbon dioxide in the atmosphere? Calculate using the ‘Law of partial pressures’.
PCO2 = FCO2 x PB
PCO2 = 0.03% x 760
0.3mmHg
What is the pressure of nitrogen in the atmosphere? Calculate using the ‘Law of partial pressures’.
PN2 = FN2 x PB
PN2 = 79% x 760
= 601mmHg
Calculate the barometric pressure by demonstrating Dalton’s law.
PB = PO2 +PCO2 + PN2
=159+0.3+601
=760mmHg
Barometric pressure changes depending on altitude, how does this affect a person’s respiratory system?
The higher the altitude, the lower the pressure of the air. On Mt Everest per say, this means there is a massive reduction in partial pressure of oxygen, making it harder to get sufficient amounts of oxygen to the tissues.
If a diver descended into the ocean, higher pressures need to be balanced by lower volumes. A diver’s lung volume is thus much lower when they are underwater compared with when they are on land.
It’s for this reason that when you are too far deep into the dive, at some points the lungs will collapse and you die.
How does the intrapleural space keep the lungs expanded?
The intrapleural space is always negative in relation to the atmosphere, this forces lungs to go outwards (as opposed to being pressured down), thus lungs expand.
Therefore when inspiring air, you want lungs to expand further, so intrapleural pressure decreases further.
When expiring air, you want a less negative intrapleural space so lungs contracts slightly.
Explain pneumothorax by first explaining the intrapleural pressure.
The pressure in the pleural cavity (between visceral and parietal pleura) is named the intrapleural pressure. This pressure is sub-atmospheric (below atmospheric) due to the lungs tending to collapse and chest wall tending to bow out, the chest and lungs pull equally on one another, causing negative pressures.
If these sub-atmospheric pressures are lost, the chest and lungs will move towards their tendencies, so lungs will collapse - called pneumothorax.
Discuss the process of inspiration, briefly include the muscles contracting, the intrapleural pressure, Boyle’s Law and pressure gradients.
The diaphragm and other inspiratory muscles contract and expiratory muscles relax, causing the thorax to increase in size.
The intrapleural pressure decreases, causing more lung expansion. Lung compliance and the fact that the pleural layers have a tendency to pull together also contribute to expansion.
This increase in volume is balanced with a decrease in pressure according to Boyle’s law where volume is inversely related to pressure.
This decrease in pressure at the alveoli allows a pressure gradient with the atmosphere, causing air to flow into the lungs.
Discuss the process of expiration, briefly include muscles relaxing, intrapleural pressure, Boyle’s Law and pressure gradients.
Inspiratory muscles relax (and perhaps forcing expiration, expiratory muscles contracting) causes the thorax to decrease in size.
Intrapleural pressure becomes less negative.
Lungs contract due to this intrapleural pressure change, also the natural recoil of the elastic lungs aids this process.
According to Boyle’s Law, this decrease in alveolar volume, means an increase in alveolar pressure.
When the alveolar pressure is higher than atmospheric pressure, there will be a pressure gradient that will cause air to flow out of the lungs.
