External and Internal Respiration

Learning Outcomes: Analyse internal and external respiration State location Describe conditions (ph, temperature) Describe roles of oxyhemoglobin, carbaminohemoglobin, reduced hemoglobin, bicarbonate ions, carbonic anydrase Write Chemical equations for external and internal respiration

4 Levels of respiration Breathing External respiration- in the lungs (what gas exchange occurs here?) Internal respiration - in the tissues Cellular respiration - in the mitochondria of cells (what is used and produced?)

Fig. 15.8

Fig. 15.4

Fig. 13.15

1. External (lungs): O2 O2 diffuses from the alveoli into the blood (why?) What molecule in the blood does O2 bind to? O2 binds to hemoglobin to form oxyhemoglobin Hb + O2 HbO2

Binding of O2 to hemoglobin occurs best at lower temperature, higher pH and higher PO2 (oxygen pressure) of the lungs

Fig. 15.9

2. Internal (tissues): O2 O2 dissociates from Hb, leaving deoxyhemoglobin HbO2 Hb + O2 Bond is weaker due to higher temperature, lower pH and lower PO2 O2 diffuses into tissue fluid and cells, where it is used for cellular respiration

3. Internal (tissues): CO2 What process produces CO2? CO2 is produced by cellular respiration in all cells CO2 diffuses out of cells into tissue fluid, and then into capillaries A small amount combines with Hb to form carbaminohemoglobin Hb + CO2 Hb CO2

Most CO2 combines with H2O to form carbonic acid, which dissociates to form hydrogen ions and bicarbonate ions: CO2 + H2O H2CO3 H+ + HCO3- This reaction is catalyzed by the enzyme carbonic anhydrase (found in red blood cells)

HCO3- is carried in the plasma H+ is picked up by hemoglobin, forming reduced hemoglobin: H+ + Hb HHb This prevents too much acidity in the blood

4. External (lungs): CO2 Bicarbonate ions release CO2 : H+ + HCO3- H2CO3 H2O + CO2 Carbaminohemoglobin releases CO2 CO2 diffuses out of the capillaries into the alveoli, to be breathed out