1 / 12

Gas Exchange, O 2 and CO 2 Transport

Gas Exchange, O 2 and CO 2 Transport. Fiona Gilmour SHO 20/05/04. Gas Exchange. For adequate gas exchange Alveoli must be ventilated Capillaries must be perfused Gases normally exchanged are CO 2 and O 2 Normal O 2 consumption 250-300ml/min Normal CO 2 production 200-250ml/min

noah-cervantes
Télécharger la présentation

Gas Exchange, O 2 and CO 2 Transport

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Gas Exchange, O2 and CO2 Transport Fiona Gilmour SHO 20/05/04

  2. Gas Exchange • For adequate gas exchange • Alveoli must be ventilated • Capillaries must be perfused • Gases normally exchanged are CO2 and O2 • Normal O2 consumption 250-300ml/min • Normal CO2 production 200-250ml/min • Tidal volume is 500mls, 2/3 used for gas exchange • 1/3 physiological dead space

  3. Ratio of CO2 produced to O2 consumed is the respiratory exchange ratio. In steady state this equals the repiratory quotient RQ 0.82 • R = VCO2 / VO2 • Gas consumption or production can be calculated • VO2 = VE (FIO2 – FEO2) • VCO2 = VE x FECO2 • O2 extraction coefficient • VO2 / VI x FIO2 x 100 • At rest this is 15-20%

  4. Gas Exchange • Alveolar gas composition determined by • inspired gas composition • alveolar ventilation • Metabolism • PAO2 = PIO2 – PACO2 / R • Mean alveolar PO2 = 100mmHg • Mean alveolar PCO2 = 40mmHg • PAO2decreases if PIO2 decreases • PACO2 decreases in hyperventilation and increases in hypoventilation

  5. Fick’s Law of Diffusion • Gas movement across blood/gas barrier and blood/tissue barrier occurs by diffusion down partial pressure gradient • depends on • Molecular weight and solubility of the gas • surface area available • thickness of barrier (distance travelled)

  6. Diffusion • Lung is ideal for diffusion • Large surface area (50-100 sqm) • Very thin blood gas barrier (0.3microm) • Sufficient contact time occurs in alveoli to permit capillary blood to have same partial pressure as alveolar gas • CO2 diffuses 20X more rapidly than O2 • Higher solubility but similar molecular weight

  7. Oxygen Transport • 99% total O2 carried in RBC • 1% in physical solution • for each mmHg PO2 there is 0.03ml O2/L blood • normal arterial blood (100mmHg) contains 3mlO2/L • Amount of O2 per litre of blood depends on Haemoglobin concentration and degree of saturation which depends on PO2 • PO2 95mmHg Hb 97% saturated • PO2 40mmHg Hb 70% saturated

  8. Haemoglobin • Globular protein • 4 subunits • Haem group in polypeptide chain • 4 polypeptide chains = globulin • Each molecule of Hb can bind 4 molecules of O2 • Oxyhaemoglobin is red • Deoxyhaemoglobin is purple

  9. Haemoglobin • Attachment of 1 O2 facillitates uptake of subsequent O2 • Haem-haem interaction • Amount of O2 bound to Hb determined by PO2 • PCO2, pH, 2,3BPG all directly affect globin molecule and change affinity of haem for O2 and shifts curve left or right • Bohr effect

  10. CO2 Transport • Deoxygenated blood has high CO2 affinity • Oxygenation makes globin less able to combine with CO2 and H+ • Haldane effect • results in downwards and upwards shifts in CO2 dissociation curve • Blood contains 2.5 X more CO2 than O2

  11. CO2 Transport • Carried in 3 ways • Physical solution (5-6% total CO2, 10% in Venous) • Carbamino compounds (5-10%) • Bicarbonate (85-90%)

  12. CO2 Transport • H2O+CO2>H2CO3>H+ + HCO3- • slow in plasma but accelerated by carbonic anhydrase in RBC • RBC membrane impermeable to H+ so to maintain electroneutrality Chloride anion moves from plasma • Chloride shift • Deoxygenated Hb is less acid so will bind H+ and buffer cell

More Related