Hemoglobin

Question 1

Electron Transport Chain Outline

Answer 1

Question 2

Venous Oxygen Delivery Outline

Answer 2

Question 3

Oxygen consumption resting vs exercising

Answer 3

In an individual at rest, about 25% of the total oxygen is consumed, so that the remaining hemoglobin in the venous circulation is 75% saturated with oxygen. During exercise, when oxygen consumption increases, the cardiac output increases (due to a faster heart rate as well as more blood pumped with each beat). Furthermore, the degree of oxygen extraction is greater, so that the venous oxygen saturation is decreased. With intense exercise, up to 90% of the oxygen can be extracted.

Question 4

Room air composition vs alveolar air composition

Answer 4

Note that under STP, alveolar air has a reduced oxygen content due to increased carbon dioxide and water vapor partial pressures.

Question 5

Henry’s Law

Answer 5

The amount of dissolved gas is proportional to the partial pressure

[O₂] = aO₂ * PO₂

aO₂ = 0.0031 mL O_{2 x} mmHg^-1 _x dL^-1

where aO₂ is the solubility constant of molecular oxygen.

Question 6

Convention for gas dissolution in blood and standard measure

Answer 6

As a convention, we will consider the amount of oxygen dissolved in 100 mL (1 deciliter or dL) of plasma, and express this in terms of the volume of dissolved gas. When you do the math, this yields a value of 0.32 mL of oxygen/dL of plasma.

This calculation is without hemoglobin. In reality, 98.5% of the oxygen in the blood is bound to hemoglobin; only a small amount is directly dissolved.

Question 7

An average adult human body contains _____ of blood.

Answer 7

An average adult human body contains five liters of blood.

Question 8

Hemoglobin’s oxygen capacity

Answer 8

One gram of hemoglobin can bind to 1.34 mL of oxygen

Question 9

Resting bloodflow diagram

Answer 9

Question 10

Why is the heart so vulnerable to reduced blood flow caused by narrowing of the coronary arteries?

Answer 10

Because the heart extracts a large fraction of available oxygen (70%) from a small portion of blood which passes through it. If this supply is cut off, the organ may become rapidly hypoxic.

Question 11

Exercising bloodflow diagram

Answer 11

Question 12

Myoglobin O₂ binding

Answer 12

Question 13

Oxygen-Myoglobin Dissociation Curve

Answer 13

P₅₀ = 2.75 mm Hg for myoglobin

Question 14

Oxygen-Hemoglobin Dissociation Curve

Answer 14

P₅₀ = 27 mmHg for hemoglobin

Question 15

30-60, 60-90

Answer 15

At a PO₂ of 30, hemoglobin is 60% saturated, and at a PO₂ of 60, hemoglobin is 90% saturated.

Question 16

Cytochrome C oxidase is most active at a PO₂ of . . .

Answer 16

10 mm Hg

Question 17

T and R state for hemoglobin

Answer 17

Question 18

Facilitators of T state

Answer 18

2,3-bisphosphoglycerate (2,3-BPG): Small, heavily anionic molecule which nests into hemoglobin and interacts with cations in the two beta chains to force a T conformation.

Acidic conditions: Result in protonation of beta chain histidines which facilitate ionic interaction between the alpha and beta chains, again forcing a T state conformation. (Remember that the lungs are typically around pH 7.4, while active metabolism in tissues may drop the pH closer to 7.0)

Also bear in mind that O₂ binding moves these ions away from one another, weakening ionic interactions and contributing to cooperative binding.

Question 19

Bohr Effect

Answer 19

Question 20

Acidic stabilization of the T state

Answer 20

Question 21

2,3-bisphosphoglycerate production

Answer 21

Question 22

2,3-bisphosphoglycerate in the T state

Answer 22

Question 23

Fetal Hemoglobin

Answer 23

Question 24

Oxygen-Hemoglobin F Dissociation Curve

Answer 24

Question 25

Why won’t a pulse oximiter give a good reading if the patient is breathing hyperbaric or concentrated oxygen?

Answer 25

It does not account for the oxygen that is dissolved in solution, free of hemoglobin. Under standard conditions, this is negligible, but if alveolar PO₂ is high, it may become clinically relevant.

Question 26

How can the kidneys affect blood oxygen content?

Answer 26

Kidneys may sense a decreased level of oxygen delivery and secrete erythropoietin from the juxtaglomerular cells, stimulating erythropoiesis and thus increasing the amount of hemoglobin available to transport O₂.