Transport and exchange of O

2 and CO

2

Lungs: pH 7.4 Temp 37 °CTissues: pH 7.38Temp 38 °C

In the lungs: external respiration Gas moves as a result of concentration

gradient Rise in concentration of O

2 in alveolus causes

diffusion of O2 into capillary

High CO2 in capillary causes diffusion of CO

2

into alveolus Gases move from high to low concentration or

high to low partial pressure Note: before CO

2 can diffuse out it must come

out of solution; blood becomes less acidic in lungs

In the tissues: internal respiration

O2 is low in tissues because it is used up

during aerobic cellular respiration O

2 diffuses into tissues (leaving RBC's)

CO2 diffuses into capillary

Blood and transporting O2(and CO

2)

Most O2 is carried by hemoglobin on RBC's

Without Hb, blood would only carry 1/60th amount of O

2

O2 combines with iron portion of Hb

Hb is a quaternary structure Each Hb molecule can carry up to 4 O

2

molecules

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Hb binds with O2 at high O

2 pressure (lungs)

Hb releases O2 at low O

2 pressure (tissues)

O2 binding with HB is facilitated in cooler temps and neutral pH (lungs)

Release of O2 is facilitated in the tissues by warm temp and a slightly acidic pH

External respiration: lungs

Hb + O2 → HbO

2

Reduced Hb Oxyhemoglobin

(dark purple) (bright red)

Internal respiration: tissue

HbO2 → Hb + O

2

CO (carbon monoxide) can bind with Hb irreversibly and prevents O

2 from binding

(called carbon monoxide poisoning)

Carbon Dioxide is produced in the tissues

Three ways to transport CO2

1.Most CO2 combines with H

2O and is

transported in blood plasma, dissolved as bicarbonate ion

2.A small amount of CO2 is carried by

Hb. This complex is called carbaminohemoglobin

3.About 9% of CO2 is dissolved directly

into the blood

Way #1 CO2 and H

2O

This is for internal respiration

CO2 + H

2O → H

2CO

3 → H+ + HCO

3-

Carbonic anhydrase speeds up the above reaction, ensuring that there is a net movement of CO

2 into the blood from the tissues

But H+ would change acidity, causing problems

H+ help dislodge O2 so they can move into the

tissues, then they attach to the Hb

H+ + Hb → HHb

Therefore Hb acts as a buffer

Way #1 CO2 and H

2O cont'd

This is for external respiration

At lungs H+ dislodged from Hb by O2

HHb → H+ + Hb

H+ combines with HCO3

- to form CO2 and H

2O

H+ + HCO3

- → H2CO

3 → CO

2 + H

2O

Bicarbonate Carbonic acid

Way # 2 CO2 carried by Hb

For external respiration

HbCO2 → Hb + CO

2

For internal respiration

Hb + CO2 → HbCO

2