External and Internal Respiration

Learning Outcomes:

• C10 – 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

Review – 4 Levels of respiration

• Breathing

• External respiration- in the lungs

(what gas exchange occurs here?)

• Internal respiration - in the tissues

(what gas exchange occurs here?)

• 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