External & Internal Respiration

5/18/11

External and Internal Learning Outcomes:
Respiration
•  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

Fig. 15.8

Levels of respiration

•  Breathing
•  External respiration (in the lungs)
•  Internal respiration (in the tissues)
•  Cellular respiration (in the mitochondria

of cells)

Fig. 15.4

External Respiration

•  What exchange occurs in the lungs?
•  Oxygen enters the blood from the

alveoli
•  Carbon dioxide leaves the blood and

enters the alveoli

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Internal Respiration

•  What exchange of gases occurs at the
tissues?

•  Oxygen leaves the blood diffuses first
into tissue fluid, then into cells

•  Carbon dioxide diffuses from cells to
tissue fluid and into the blood

Fig. 13.15

1. External (lungs): O2

•  O2 diffuses from the alveoli into the
blood (why?)

•  What molecule in th→e blood does O2
bind to?

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•  O2 binds to hemoglobin to form
oxyhemoglobin

•  Hb + O2 → HbO2

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Fig. 15.9

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

2. Internal (tissues): O2 3. Internal (tissues): CO2

•  O2 dissociates from Hb, leaving •  What process produces CO2?
deoxyhemoglobin •  CO2 diffuses out of cells into tissue fluid,

•  Hb O2 →Hb + O2 and then into capillaries
•  A small amount combines with Hb to
•  Bond is weaker due to higher
temperature, lower pH and lower PO2 form carbaminohemoglobin

•  O2 diffuses into tissue fluid and cells, •  Hb + CO2 → Hb CO2

€ where it is used for cellular respiration €

•  Most CO2 combines with H2O to form •  HCO3- is carried in the plasma
carbonic acid, which dissociates to form •  H+ is picked up by hemoglobin, forming
hydrogen ions and bicarbonate ions:
reduced hemoglobin:
→ →•  CO2 + H2O H2CO3 H+ + HCO3-
•  H+ + Hb →HHb
•  This reaction is catalyzed by the
•  This prevents too much acidity in the
enzyme carbonic anhydrase (found in blood

red blood cells) €

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4. External (lungs): CO2

•  Bicarbonate ions release CO2 :

→ →•  H+ + HCO3- H2CO3 H2O + CO2

•  CO2 diffuses out of the capillaries into
the alveoli

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