West's 9th ed - Chapter 6 - Oxygen and Dissociation (1) Flashcards
What is Henry’s Law?
Henry’s Law states that the amount of a gas dissolved in the blood is proportional to its partial pressure. Both oxygen and CO2 obey Henry’s Law.
What is the amount of O2 dissolved in blood, expresed in mL/100mL, when the PO2 is 100mmHg?
0.3mL O2/ 100mL of blood
Briefly describe the two components of haemoglobin: Heme and Globin
Heme is an iron-porphyrin compound. Globin is a protein which consists of four polypeptide chains, each attached to their own heme group.
To which part of haemoglobin does each O2 molecule bind? How many O2 molecules can bind?
One O2 molecule binds to each of the four ferrous iron ions (Fe2+). Each of the four polypeptide subunits contains one haem group. Each haem group contains one Fe2+. This means that each molecule of Hb can bind four O2 molecules.
What meant by the O2 capacity? What is its usual value?
O2 capacity is the maximum amount of O2 that can be combined with Hb. In a normal subject, it is about 20.8mL O2 / 100mL of blood (assuming Hb = 15g/dL)
What is meant by the O2 saturation of blood?
This refers to the percentage of the available binding sites that have O2 attached
How much O2 can combine with 1g pure Hb?
1.39mL
What is the equation for the oxygen concentration of blood (in mL O2 / dL of blood)?
(1.39 x Hb x Sat/100) + 0.003(PO2)
Hb is measured in g/dL
What is on the x-axis of the O2-dissociation curve?
PO2 (mmHg)
What is on the y-axis of the O2-dissociation curve?
%ge of Hb saturation
If the O2-dissociation curve is shifted to the right, what does this suggest about the change in O2-affinity of Hb?
The O2 affinity of Hb is lower
Name 4 factors that will shift the O2-dissociation curve to the right.
1) Increased H+ concentration
2) Increased pCO2
3) Increased temp
4) Increased concentration of 2,3-DPG
Think of an exercising muscle: what factors about it change the O2-affinity of Hb?
An exercising muscle is hot, acidic, and hypercarbic. This environment shifts the O2-dissociation curve to the right, and makes O2 offloading to the tissues easier.
What is 2,3-DPG?
2,3-diphosphoglycerate is an end-product of red cell metabolism. It binds to beta chains of deoxyhaemoglobin, and it decreases the O2-affinity of Hb. It has a half-life of 6hrs.
Under what conditions is the concentration of 2,3-DPG in the red cells increased?
Chronic hypoxia (e.g. altitude, anaemia, chronic lung disease) or hypoxia of exercise. Its shifting of the O2-dissociation curve makes it easier to unload O2 into the tissues.
Also:
Thyroid hormones
Growth hormones
Androgens
