Gas exchange

• Describe external respiration

  The diffusion of oxygen from the alveoli to pulmonary capillaries. Carbon dioxide diffuses in the opposite direction.
• Describe internal respiration

  Oxygen diffuses from systematic capillaries into the tissues, and carbon dioxide diffuses in the opposite direction.
• How is gas exchange affected in exercise

  Blood flow increases leaving less time for diffusion.
• What type of transport is utilised in gas exchange

  Passive diffusion
• Why is the PO2 not diffusion-limited

  Blood is in contact with the alveoli for 0.75 seconds. PO2 reaches equilibrium in 0.25 seconds.
• What is Dalton's law


  The total pressure of a gas mixture is equal to the sum of the pressure of each gas in it.
• What can be worked out according to Dalton's Law

  The total pressure of a gas mixture.

  The partial pressure of an individual gas within a gas mixture.
• How do you work out total pressure

  Total pressure = PA + PB
• How do you work out partial pressure of Oxygen in the atmosphere

  PO2 = 760 * 21% = 159 mmHg
• What is the pressure of the atmosphere

  760 mmHg
• What is the partial pressure of oxygen in the atmosphere

  159 mmHg
• What is the partial pressure

  The pressure of a gas within a gas mixture.
• What is the percentage of Nitrogen in the air 


  78.09
• What is the percentage of oxygen in the air 


  20.95
• What is the percentage of inert gases in the air


  0.93
• What is the percentage of carbon dioxide in the air


  0.03
• What are the main components of air

  Nitrogen. Oxygen. Inert gases. Carbon dioxide.
• What is one atmosphere

  750 mmHg
• What is the pressure at sea level in mm Hg


  760
• What is the stimulus for increased ventilation at altitude

  A reduction in the PO2
• What is the stimulus for increased ventilation at sea level

  An increase in PCO2.
• What is the respiratory membrane made of

  Alveolar walls and blood vessel walls.
• What respiration occurs across the respiratory membrane

  External
• What is the main feature of alveolar walls

  They contain elastic fibres which allow them to move and stretch.
• What are the role of dust cells in alveoli

  These are macrophages which filter the air.
• How many pulmonary alveolar epithilium cells are there

  3
• How many alveolar cells are there

  2
• What is laplace's law


  It states that the pressure collapsing the alveoli is directly proportional to surface tension but inversely proportional to the radius.
• What is the equation for laplace's law

  P = 2 * T/r. Where P is translung distending pressure. T is wall surface tension. R is radius.
• What is the role of Type 2 alveolar cells

  To produce lipid-rich surfactant. This decreases the surface tension of the fluid lining the alveoli. Resulting in a decrease in the distending pressure. Hence, it prevents lung collapse upon inflation.
• When is surfactant first produced

  26 weeks prenatally.
• What is respiratory distress syndrome in newborns

  Premature infants are vulnerable to lung collapse as they have not yet started to produce surfactant.
• What is the treatment for RDS

  Oxygen
• How is surfactant production stimulated for a mother in labour

  Cortisol treatments
• What alveolar cell type is part of the respiratory membrane

  1
• What is the inteterstial space

  It is an area of elastic fibres within the respiratory membrane
• What factors affect gas exchange

  Surface area. Diffusion distance. Diffusion gradient.
• What are the features of alveoli surface are

  Large and spherical.

  Inflation increases the surface area for gas exchange.

  There are multiple small alveoli which increase surface area.
• What happens to alveoli in emphysema

  Alveoli walls are degraded resulting in a smaller surface area for gas exchange.
• What are the features of alveoli diffusion distance

  Short but can increase if fluid or mucus is in the lungs.