Respiration External Respiration: exchange of O2/CO2 between air/blood at alveoli Internal Respiration: exchange of O2/CO2 between blood & tissue fluid Cellular Respiration: production of ATP in mitochondria: requires O2 , releases CO2

External Respiration - alveoli/capillary walls are one cell layer thick - gas exchange occurs by diffusion alone - tissue fluid in alveoli [O2] ↑ to ↓ , [CO2] ↓ to ↑ - blood in alveoli capillaries [O2] ↓ to ↑, [CO2] ↑ to ↓ Hemoglobin: iron-containing respiratory pigment found in red blood cells, ↑ O2 carrying capacity of blood 60 times ~ 200 million hemoglobin molecules per RBC, each composed of 4 polypeptide chains connected to 4 heme groups (contain iron), 4 O2 bind per Hb - - can carry O2, CO2, H+, CO (prevents normal respiration)

External Respiration - most CO2 carried in blood as bicarbonate ion (HCO3-), CO2 leaves blood in reaction catalyzed by enzyme carbonic anhydrase (red blood cell) blood to alveoli H+ + HCO3- → H2O+ CO2 carbonic anhydrase - small amount of CO2 in blood carried by hemoglobin (carbaminohemoglobin) HbCO2 → Hb + CO2 blood to alveoli - Hb takes up O2 in ↑ amounts as pressure of O2 ↑ until ~100 mm Hg alveoli to blood Hb + O2 → HbO2 (oxyhemoglobin)

External Respiration Temperature Effects: - Hb takes up O2 more readily in ↓ temperature lungs - Hb gives up O2 more readily in ↑ temperature tissue

External Respiration pH Effects: - Hb takes up O2 more readily in more basic/neutral lungs - Hb gives up O2 more readily in more acidic tissues

Internal Respiration - tissue fluid has ↓O2 due to cellular respiration: O2 diffuses into tissue blood to tissue (oxyhemoglobin) HbO2 → Hb + O2 (deoxyhemoglobin) - some CO2 from cellular respiration taken up by hemoglobin in blood (carbaminohemoglobin) HbCO2 → Hb + CO2 tissue to blood - most CO2 combines with H2O to form carbonic acid dissociates to H+, HCO3- (bicarbonate) tissue to blood RBC plasma H2O + CO2 → H2CO3 → H+ + HCO3- (carbonic anhydrase) buffer, keeps blood pH constant