1. 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

2. 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)

3. 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)

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

6. 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

7. 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