Transport of Oxygen and carbon dioxide

1. Transport of Oxygen and carbon dioxide

2. Learning objectives At the end of this session students should be able to • Define oxygen partial pressure (tension), oxygen content, and percent hemoglobin saturation as they pertain to blood. • Interpret an oxyhemoglobin dissociation curve (hemoglobin oxygen equilibrium curve)

3. Learning objectives • Show how the oxyhemoglobin dissociation curve is affected by changes in blood temperature, pH, PCO2, and 2,3-DPG. • List the forms in which carbon dioxide is carried in the blood. Identify the percentage of total CO2 transported as each form. • Interpret the carbon dioxide dissociation curves for oxy- and deoxyhemoglobin. • Describethe interplay between CO2 and O2 binding on hemoglobin that causes the Haldane effect.

4. Oxygen uptake in the lungs

6. O2 Transport in blood

7. Dissolved form:

9. Combined form with hemoglobin

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

13. Pulse oximetry • Hb changes color from dark blue to bright red when O2 binds, which makes it possible to monitor arterial O2-saturation levels using noninvasive pulse oximetry. • A light-emitting probe is attached to a finger or ear, then the relative amounts of saturated and desaturatedHb is calculated from the amount of light absorbed at 660 nm and 940 nm, respectively.

15. The blood of a normal person contains about 15 grams of hemoglobin in each 100 milliliters of blood, and each gram of hemoglobin can bind with a maximum of 1.34 milliliters of oxygen. • There-fore, 15 times 1.34 equals 20.1 • On average, the 15 grams of hemoglobin in 100 millilitersof blood can combine with a total of almost exactly 20 milliliters of oxygen if the hemoglobin is 100 per cent saturated • On passing through the tissue capillaries, this amount is reduced, on average, to 14.4 milliliters(Po2of 40 mm Hg, 75 per cent saturated hemoglobin). • Thus, under normal conditions, about 5milliliters of oxygen are transported from the lungs to the tissues by each 100 milliliters of blood flow.

16. Co-efficient of O2 utilisation

17. P 50

23. Aerobic metabolism generates CO2 and causes tissue Pco2 to rise. CO2binds 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

24. BOHR EFFECT

27. CO poisoning

28. CO poisoning • CO decreases O2bound to hemoglobin and also causes a left shiftof 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

31. Use the following diagram of oxyhemoglobin saturation curves

32. What is the P50of the oxyhemoglobin curve labeled A in the diagram? a. 80 mmHg b. 60 mmHg c. 40 mmHg d. 30 mmHg e. 20 mmHg Which of the following conditions is most likely to shift the above oxyhemoglobin curve from A to B? a. Increased temperature b. Exercise c. Acclimatization to high altitude d. Hyperventilation e. Metabolic acidosis

33. Which of the following conditions causes a decrease in arterial O2 saturation without a decrease in O2tension? a. Anemia b. Carbon monoxide poisoning c. A low V/Q ratio d. Hypoventilation e. Right-to-left shunt

35. Which one of the above oxyhemoglobin saturation curves was obtained from fetal blood? a. A b. B c. C d. D e. E

36. Which one of the above oxyhemoglobin saturation curves was obtained from blood exposed to carbon monoxide? a. A b. B c. C d. D e. E

37. TRANSPORT OF CARBON DIOXIDE

40. Transport of Carbon dioxide Dissolved Carbon Dioxide 5% 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 5% of the total CO2 is carried as carbamino compounds. The attachment sites that bind CO2 are different from the sites that bind O2.

41. BOHR EFFECT

42. Bicarbonate About 90% 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.

43. 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