Gas Exchange and Transportation

Question 1

describe the two methods by which O2 is carried in the blood and indicate the relative importance of each

Answer 1

1. less than 2% is dissolved in plasma, but this is the blood PO2 we measure
2. greater than 98% is in RBCs, combined with hemoglobin (Hb-O2)

Question 2

describe how hemoglobin and iron in the heme molecule function to carry O2 in the blood

Answer 2

the hemoglobin molecule has 4 hemoglobin chains, and each of those chains has iron in the middle which (should) reversibly bind iron to form oxyhemoglobin; some, or all 4 sites can carry oxygen

Question 3

be able to label oxygen-hemoglobin dissociation curve and explain how it describes the relationship between partial pressure of oxygen and percent oxygen saturation

Answer 3

there is high hemoglobin saturation where there is high PO2 in the lungs, when hemoglobin allosterically has a high affinity for O2

there is low hemoglobin saturation where PO2 is low, in the tissues, where hemoglobin has a low affinity for O2

Question 4

explain how O2 affinity and the allosteric effect it has on the conformation of the hemoglobin molecule underlies the shape of the curve

Answer 4

one hemoglobin chain binding oxygen has an allosteric effect of changing the shape of the molecule, making it easier for the next O2 molecule to bind

Question 5

describe the underlying mechanisms by which physiologic factors such as blood pH, temperature, CO2, and 2,3-DPG levels alter the oxygen-hemoglobin dissociation curve; explain how oxygen transport in the pulmonary and systemic tissue beds is affected by these factors

Answer 5

1. lower CO2, lower 2,3-DPG, high pH, and lower temperature all cause a left shift, meaning that they cause hemoglobin to have a higher affinity for oxygen, this happens at the alveoli
2. high CO2, high 2,3-DPG, lower pH, and higher temperature all cause a right shift, meaning that they cause hemoglobin to have a low affinity for oxygen, this happens at the tissues

Question 6

explain how the oxygen-hemoglobin dissociation curve reflects the physiologic movement of O2 between the pulmonary and the systemic capillary beds

Answer 6

a left shift (high Hb-O2) is seen in the pulmonary circulation, where gas exchange is occurring

a right shift (less Hb affinity for O2) is seen in the systemic circulation, where tissues are respiring and releasing the products of metabolism (CO2, 2,3-DPG, etc.)