Electron Transport Chain Outline
Venous Oxygen Delivery Outline
Oxygen consumption resting vs exercising
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.
Room air composition vs alveolar air composition
Note that under STP, alveolar air has a reduced oxygen content due to increased carbon dioxide and water vapor partial pressures.
The amount of dissolved gas is proportional to the partial pressure
[O2] = aO2 * PO2
aO2 = 0.0031 mL O2 x mmHg-1 x dL-1
where aO2 is the solubility constant of molecular oxygen.
Convention for gas dissolution in blood and standard measure
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.
An average adult human body contains _____ of blood.
An average adult human body contains five liters of blood.
Hemoglobin's oxygen capacity
One gram of hemoglobin can bind to 1.34 mL of oxygen
Resting bloodflow diagram
Why is the heart so vulnerable to reduced blood flow caused by narrowing of the coronary arteries?
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.
Exercising bloodflow diagram
Myoglobin O2 binding
Oxygen-Myoglobin Dissociation Curve
P50 = 2.75 mm Hg for myoglobin
Oxygen-Hemoglobin Dissociation Curve
P50 = 27 mmHg for hemoglobin
At a PO2 of 30, hemoglobin is 60% saturated, and at a PO2 of 60, hemoglobin is 90% saturated.
Cytochrome C oxidase is most active at a PO2 of . . .
10 mm Hg
T and R state for hemoglobin
Facilitators of T state
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.
Acidic stabilization of the T state
2,3-bisphosphoglycerate in the T state
Oxygen-Hemoglobin F Dissociation Curve
Why won't a pulse oximiter give a good reading if the patient is breathing hyperbaric or concentrated oxygen?
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.
How can the kidneys affect blood oxygen content?
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.