PSL201 - Respiration.docx

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21 Apr 2012
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PSL201 - Respiration
Exchange of Oxygen and CO2
- in mixtures gases diffuse down their partial pressure gradient
- alveoli and blood are exchange points
Gas Exchang in the Lungs
- exchange of gases occur continuously between alveolar air and the capillary
blood
- upon inspiration fresh air enters and mixes with stale air in the deadspace
- air in alveoli is saturated with water vapor
- blood in pulmonary capillaries is deoxygenated Po2=40 mmHg and Pco2=
46mmHg
o as it passes through alveoli both gases transport across their
gradients
- eventually diffusion is reached and Pco2= 40mmHg and Po2= 100mmHg
Gas Exchange in Respiring Tissue
- blood flows back to left atrium via the pulmonary veins
- then pumped by the left ventricle (Po2= 100mmHg, Pco2= 40mmHg)
- during diffusion at tissues O2 moves into tissues and Co2 moves out
Determinants of Aveolar Pressure
- determined by 3 factors:
o the Po2 and Pco2 of inspired air
o minute alveolar ventilation (volume of fresh air to alveoli each
minute)
o the rate at which tissues consume O2 and produce Co2
O2 Transport in Blood
- hemoglobin
o consists of 4 subunits and a heme group
o hemeoglobin + O2 = oxyhemoglobin
o hemoglobin O2 = deoxyhemoglobin
- binding of oxygen is reversible
o Hb + O2 <---> Hb-O2
- High Po2 facilitates binding and low Po2 failitate release
Dissociation Curve
- sigmoidal
- increased affinity with more O2 attached
- rightwards shift: (decreased affinity)
o pH down, Co2 up, temp. down
- leftwards shift: (increased affinity)
o pH up, Co2 down, temp. up
- carbamino effect: when Co2 binds to hemoglobin reducing its affinity for O2
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