Blood Gas Transport

Question 1

Outline the forms by which O2 and CO2 are carried in blood and specify their contents in arterial and venous blood

Answer 1

O2: transporter in 2 forms:
1. physically dissolved (2%)
2. chemically bound to HGB (98%)
- relatively insoluble in blood. at PO2 of 100mmHg, 100 ml of blood contains 0.3 ml O2
O2 content arterial blood CaO2=20 mlO2/100ml blood(%)
O2 content venous blood CvO2= 15
- each time blood circulate through systemic circulation, 5ml/100ml O2 diffuses to tissues

CO2- 3 forms
1. physically dissolved in blood (7%)
2. physically dissolved as HCO3- (70%)
3. chemically bound Hb (23%)
CaCO2=48
CvCO2=52
- each time blood circulates through systemic circulation, 4ml/100ml CO2 diffuses out of tissues, delivered to lungs

Question 2

Describe the physiological significance of the oxy-hemoglobin dissociation curve. Interpret the right and left shift in the position of this curve to the affinity of hemoglobin for oxygen and its ability to load oxygen in the lungs and unload it to the tissues.

Answer 2

mixed venous blood (po2=40, 75% sat.) enters pulmonary capillary, equilibrate with alveolar po2=100, reaches 98% saturation

• plateau region (Po2=60-100) provides safety margin when Po2 is low (disease/altitude)
• increasing Po2 above 100 doesn’t improve saturation

P50= PO2 required for 50% of Hb to become bound
P50=26.6 mmHg in healthy arterial blood
- increase affinity of Hb for O2 = LEFT SHIFT
-decrease affinity for Hb= RIGHT SHIFT (easier to unbind)

Question 3

Describe the impact of PCO2, pH, temperature, 23BPG, anemia and carbon monoxide on the oxy-hemoglobin dissociation curve and interpret their physiologic outcome

Answer 3

PCO2 increase = right shift
2,3 BPG- product RBC glycolysis. increased in hypoxia. right shift. fetal Hb has higher affinity O2 (L shift) bc lower affinity for BPG, favoring oxygen delivery to fetal blood)
anemia: reduced O2 carrying capacity. reduced O2 content in blood (SaO2 remains normal)
CO: Hb affinity CO = 250x greater than O2, competes for binding. Left shift interferes with O2 unloading, leads to tissue hypoxia (decreased O2 content)

Question 4

Describe the significance of the enzyme, carbonic anhydrase, in transport of carbon dioxide in blood

Answer 4

CA resides in RBCs. accelerates formation of carbonic acid from CO2 and water

Question 5

Explain how O2 and CO2 influence the transport of each other by hemoglobin in reference to the Bohr and Haldane Effects.

Answer 5

CO2 dissociation curve influenced by oxygenation state of Hb. CO2 transport in blood depends on O2 release from Hb. if increase PO2, carries less Co2 (Haldane)
and increased pCO2 = right shift oxygen curve (Bohr)

HB is better than O2HB at binding H+ and CO2 to form CO2HHb, which helps blood load more CO2 from tissue by acting as CO2 sink