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Lecture 30
Gas Exchange
| Term | Definition |
|---|---|
| Partial Pressures | Gas equivalent to concentration. Sea level:760 mmHG=600 N2+160 O2.CO2=.03 mmHg. Gases indep of one another. Air in lungs is water saturated |
| Alveolar Air | PO2=100mmHG,PCO2=40.Venous blood:PO2=40,PCO2=46 |
| Diffusion Across Alveolar Wall | gases follow partial pressure gradients capillary gases match tissue it goes through. O2:O2 enters pulmonary capillaries until PO2 is 100. CO2:CO2 leaves pulmonary capillaries until PCO2 is 40 |
| Pulmonary Circulation | Lower BP than aorta. ~15-20mmHg of MAP pf pulmonary artery. |
| Ventilation/Perfusion Ratio | Ventilaiton and perfusion normally well matched,0.8 areas that open alveoli:get more blood. As need for gas exchange raises both and ventilation raises in new lung areas |
| Tissue Gas Exchange | Reverse of Lungs. O2:100mmHg of arterial blood loses O2 to 40mmHG tissur=e until capillary is 40mmHg. CO2:40mmHg arterial blood receives CO2 from 46mmHg tissue until capillary is 46 mmHg |
| Oxygen Transport | 1.5% carried by dissolved O2. 98.5% carried by binding to hemoglobin |
| Oxygen-Hemoglobin Binding | Sigmodal curve-cooperativity btw 4-5 subunits |
| Sleep Region | At tissues-fall in PO2-unloads O2. At lower PO2,even more O2 delivery "work hard,get oxygen" |
| Plateau Region | At lungs-all Hb is O2 bound-no effect of extra O2 |
| Bohr Effect | CO2,acid,shift Hb-O2 curve to the right. More O2 unloading at given PO2 |
| Carbon Monoxide | 2 effects. Binds Hb 200x stronger than O2-less Oa available. Never dissociates-must lyse RBC to lose CO |
| Hypoxia | Low blood O2. low air O2 air=high altitude or O2 deprivation. High altitude ethnic groups-higher Hb even at sea level.sea level ethnic groups-low O2 training raises Hb,lose when return to sea level |
| Hyperpoxia | Breathe high O2 air-no additional Hb binding (already full). raises dissolved O2 may lower breathing rate-benefit only psychological |
| Carbon Dioxide Transport | 10% dissolved, 30% bound to plasma protein and Hb. 60% converted to bicarbonate by carbonic anhydrase (CA) CA catalyzes:H2O+CO2 leads to H2CO3-HCO3- +H+ |
| Carbonic Anhydrase | In RBC's. Converts CO2 leads to bicarbonate at tissues as CO2 added. At lungs,reversal:bicarb,CO2 then breathed out |
| Hypocapnia | Low CO2 hyperventilation dec CO2 in blood leads to faint breathing into bad raises CO2,back to normal. |
| Hypercapnia | High CO2 raises breathing rate raises CO2 in blood strongest stimulus for inc respiration |
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