Transport of Oxygen and carbon dioxide

Oxygen uptake in the lungs

O2 Transport in blood

Dissolved form:

Combined form with hemoglobin

Diffusion of oxygen from a tissue capillary to the cells. (Po2 in interstitial fluid = 40 mm Hg, and in tissue cells = 23 mm Hg.)

P 50

• Aerobic metabolism generates CO2 and causes tissue Pco2 to rise. CO2 binds to terminal globin amino groups and decreases Hb’s O2 affinity.

• The Hb–O2 dissociation curve shifts to the right, and O2 is unloaded.

• CO2 also dissolves in water to yield free acid, which promotes further O2 unloading via the Bohr effect

BOHR EFFECT

CO poisoning

CO poisoning

• CO decreases O2 bound to hemoglobin and also causes a left shift of the O2-hemoglobin dissociation curve.

• CO binds to hemoglobin with an affinity that is 250 times that of O2 to form carboxyhemoglobin.

• the presence of CO decreases the number of O2-binding sites available on hemoglobin.

• Reduces O2 content of blood and O2 delivery to tissues

Use the following diagram of oxyhemoglobin saturation curves

What is the P50of the oxyhemoglobin curve labeled A in the diagram?

a. 80 mmHgb. 60 mmHgc. 40 mmHgd. 30 mmHge. 20 mmHg Which of the following conditions is most likely to shift the

above oxyhemoglobin curve from A to B?a. Increased temperatureb. Exercisec. Acclimatization to high altituded. Hyperventilatione. Metabolic acidosis

Which of the following conditions causes a decrease in arterial O2 saturation without a decrease in O2 tension?

a. Anemiab. Carbon monoxide poisoningc. A low V/Q ratiod. Hypoventilatione. Right-to-left shunt

Which one of the above oxyhemoglobin saturation curves was obtained from fetal blood?

a. Ab. Bc. Cd. De. E

Which one of the above oxyhemoglobin saturation curves was obtained from blood exposed to carbon monoxide?

a. Ab. Bc. Cd. De. E

TRANSPORT OF CARBON DIOXIDE

Transport of Carbon dioxideDissolved Carbon Dioxide• 7% of the total CO2 content of blood• Carbon dioxide is 20 times more soluble in blood than oxygen is. Carbamino Compound• Carbon dioxide reacts with terminal amine groups of proteins(Hb)

to form carbamino compounds.• The protein involved appears to be almost exclusively hemoglobin

and this binding is responsible for Bohr effect.• Reversly, O2 bound to Hb changes its affinity for CO2, such that

when less O2 is bound, the affinity of hemoglobin for CO2 increases called the Haldane effect.

• About 7% of the total CO2 is carried as carbamino compounds. The attachment sites that bind CO2 are different from the sites that bind O2.

BOHR EFFECT

Bicarbonate• About 70% of the CO2 is carried as plasma

bicarbonate.• In order to convert CO2 into bicarbonate or the

reverse, carbonic anhydrase (CA) enzyme must be present.

• Plasma contains no carbonic anhydrase; therefore, there can be no significant conversion of CO2 to HCO3- in this compartment.

• All of the reactions described here occur in reverse in the lungs.

• H+ is released from its buffering sites on deoxyhemoglobin, HCO3 - enters the red blood cells in exchange for Cl-.

• H+ and HCO3- combine to form H2CO3, and H2CO3 dissociates into CO2 and H2O. The regenerated CO2 and H2O are expired by the lungs