Respiratory Physiology 4.3- Additional material on oxygen carriage in blood Flashcards
Define arterial partial pressure?
Arterial partial pressure of O2 (PaO2 ) is not the same as arterial O2 content. PaO2 refers purely to O2 in solution in the plasma and is determined by O2 solubility and the partial pressure of O2 in the gaseous phase that is driving O2 into solution.
What are the values assigned to the partial pressure of a gas in solution?
Values assigned to the partial pressure of a gas in solution are equal to the partial pressure in gaseous phase when the number of oxygen molecules moving from the gaseous phase to the liquid phase equals the number of oxygen molecules moving in the opposite direction.
Why is partial pressure of oxygen said to be 100mmHg?
e.g. O2 solubility in water is low 0.03ml/L/mmHg
We have 3ml/L plasma so therefore partial pressure that is driving O2 into the liquid phase in plasma must be 100mmHg (3/0.03=100)
(i.e. equal to the partial pressure at the alveoli)
So PaO2 is also said to be 100mmHg (aka oxygen tension)
Describe how the concentration of oxygen mols per litre is different in the gaseous phase than the liquid phase?
30 x more molecules of oxygen in 1L gas than 1L plasma
How do gases travel in plasma?
do not travel in gaseous phase. If they did there would be bubbles in blood and could lead to fatal air embolism.
-In solution instead
How many mls of oxygen bind to each gram of haemoglobin?
1.34ml of oxygen binding to each gram of haemoglobin.
Oxygenation not oxidation
What are the forms of haemoglobin in our red blood cells?
92 percent of the haemoglobin that is in our red blood cells is in the form of adult haemoglobin
Remaining 8 percent made up of a cocktail of different types of haemoglobin:
HBA2 - delta chains replace beta chains
HbF (gamma chains replace beta chains)
Glycosylated Hb ( when exposed to high levels of glucose)
What is myoglobin and where is it found?
another oxygen carrier molecule
tends to store oxygen instead of carry
made up of one polypeptide chain
binds oxygen more tightly than haemoglobin does
found exclusively in cardiac and skeletal muscle
Why do foetal haemoglobin and myoglobin have a higher affinity for oxygen than normal adult haemoglobin?
necessary for extracting oxygen from maternal/ arterial blood
What are the five main types of hypoxia?
hypoxaemic hypoxia
anaemic hypoxia
stagnant hypoxia
histotoxic hypoxia
metabolic hypoxia
Describe hypoxaemic hypoxia?
most common.
reduction in oxygen diffusion at lungs either due to pathology or it can be due to a decrease in the oxygen partial pressure in the atmosphere
Describe anaemic hypoxia?
reduction in the oxygen carrying capacity of the blood due to anaemia (red blood cell loss/iron deficiency)
Describe stagnant hypoxia?
heart disease results in ineffecient pumping of blood to lungs/ around body
Describe histotoxic hypoxia?
poisoning prevents cells utilising the oxygen that is delivered to them.
Describe metabolic hypoxia?
oxygen delivery to the tissues does not meet increased oxygen demand by cells
