Flashcards in Oxygen in the Blood Deck (13):
What is the concentration of a dissolved gas equal to?
Concentration of a dissolved gas = it’s solubility x it’s partial pressure
What is the oxygen demand of our body at rest?
At rest our body requires about 13mmol per minute of oxygen.
What does total oxygen content of the body include?
When discussing the total content of oxygen in the blood we include both the bound oxygen and the dissolved oxygen.
What is Myoglobin?
Myoglobin is a monomer and can carry one molecule of oxygen it is a pigment found in muscles and contains haem.
Myoglobin saturates at a relatively low pO2. This is too low for it to drop off oxygen at the tissues.
Describe Haemoglobin and it's states?
Haemoglobin is a tetramer and can carry 4 molecules of oxygen. It has two states a tense (T) and a relaxed (R) state. When PO2 is low Hb is more likely to be in its tense T state. It is hard for the first O2 molecules to bind but as each oxygen molecules do bind it becomes easier as the haemoglobin molecule unwinds. This gives it the characteristic sigmoid shapes dissociation curve.
What PP does haemoglobin associate/dissociate at?
Hb saturates above 9-10kPa, is unsaturated completely under 1kPa and is half saturated around 3.5-4kPa.
How saturated is Hb in different parts of the body?
In the lungs pO2 is about 13.3kPa so Hb is completely saturated, in the tissues it is around 5kPa s saturation reaches about 65%.
In mixed venous blood half, the oxygen is still bound but some areas of the body will use more it simply depends upon what the partial pressure is at the individual tissues. This creates an oxygen reserve which can be used in exercise.
How does capillary oxygen concentration effect its ability to enter into cells and how can capillaries over come this?
pO2 of oxygen cannot get lower than 3kPa in the capillary tissues otherwise there will be no driving force of oxygen into the cells. However, the higher the capillary density the lower pO2 can fall because it doesn’t have to diffuse as far.
What is the Bohr Shift?
Bohr shift - pH effects the affinity of Hb as acidic conditions shift the dissociation curve to the right. This is because lower pH promotes the T state and higher pH promotes the R state. In metabolically active tissues pH is generally lower so extra O2 is given up.
How does temperature change the dissociation curve?
Increased temperature also shifts the dissociation curve to the right and again metabolically active tissues have slightly higher temperatures.
What importance does 2, 3-BPG have with haemoglobin?
2, 3-BPG (2, 3-DPG) is a molecule that is found in red blood cells. It’s levels increase with anaemia or at high altitude because it shifts the Hb dissociation curve to the right. Levels of the substance decreases in stored blood limiting how muchO2 can be given off but this isn’t usually a problem clinically.
What does CO do to Hb and when does it become fatal?
Carbon monoxide binds irreversible with Hb increasing its affinity for oxygen so that the Hb molecules won’t give up their oxygen to tissues. Fatal is COHb% > 50%.