BIOM1060 Lecture 27: Respiration (Gas exchange and gas transport)
BIOM1060 18/04/18
RESPIRATORY PHYSIOLOGY
GAS EXCHANGE AND GAS TRANSPORT
Gas exchange
- Simple passive diffusion of O2 and CO2 down partial pressure gradients
- Occurs at pulmonary-capillary and tissue-capillary levels
Partial pressure = pressure single gas exerts in mix of gases
Hery’s la
- Amount of particular gas in solution directly proportional to partial pressure of gas
o No net diffusion when Pair = Psolution (dependant on partial pressure and solubility)
Factors influencing rate of gas transfer
- Partial pressure: increased pressure gradient = increased rate
- Surface area: increased surface area = increased rate)
- Thickness of membrane: increased thickness = decreased rate (due to pneumonia,
pulmonary oedema or fibrosis)
- Diffusion coefficient
Diffusion coefficient (D)
- Constant related to solubility of particular gas in lung tissue and its molecular weight
o D for CO2 is 20x that of O2 (20x more soluble in body tissues)
▪ Rate of CO2 diffusion across respiratory membrane 20x more rapid
▪ Difference in D offset by difference in partial pressure (normally equal
amounts of O2 and CO2 exchanged)
Gas transport
- O2 in blood transported in combination with haemoglobin or dissolved in plasma
- CO2 transported in blood as bicarbonate
Haemoglobin
- Pigment in red blood cells
- 4 globin chains: each contain a heme molecule (Fe2+ in centre of molecule)
o O2 loosly bind to Fe2+ (one molecule carry 4 oxygen molecules until fully saturated)
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Document Summary
Simple passive diffusion of o2 and co2 down partial pressure gradients. Partial pressure = pressure single gas exerts in mix of gases. Amount of particular gas in solution directly proportional to partial pressure of gas: no net diffusion when pair = psolution (dependant on partial pressure and solubility) Partial pressure: increased pressure gradient = increased rate. Surface area: increased surface area = increased rate) Thickness of membrane: increased thickness = decreased rate (due to pneumonia, pulmonary oedema or fibrosis) O2 in blood transported in combination with haemoglobin or dissolved in plasma. 4 globin chains: each contain a heme molecule (fe2+ in centre of molecule: o2 loosly bind to fe2+ (one molecule carry 4 oxygen molecules until fully saturated) Pulmonary capillaries: haemoglobin fully saturated (po2 = 100mm hg) Systemic capillaries: 75% haemoglobin saturation - 25% offloaded into tissue (po2 = Relationship between haemoglobin saturation and po2 not constant.
