3.2.7 TRANSPORT OF OXYGEN (completed)
Approximately how many molecules of haemoglobin are there in one red blood cell
280 million (RBC can carry over a billion oxygen molecules)
How is the haemoglobin produced by a baby after birth different from haemoglobin produced by a fetus? Why must it change?
A fetus has haemoglobin with higher affinity for oxygen, so that it can take up oxygen in the placenta, where oxygen tension is low. In a baby, this form of haemoglobin is not needed as the oxygen tension in the lungs is higher
How is haemoglobin of mammals in high altitudes different from haemoglobin of mammals in low altitudes and why?
Air is less dense at high altitudes so there is less oxygen available, so the haemoglobin must have a higher affinity for oxygen
How is oxygen absorbed into the blood?
As it passes the alveoli, oxygen molecules diffuse into the blood plasma & enter red blood cells
How does partial pressure of oxygen affect how readily oxygen associates with haemoglobin?
At low partial pressure of oxygen, haemoglobin does not readily associate with oxygen molecules When partial pressure of oxygen rises, the diffusion gradient into the haemoglobin molecule increase
Why does haemoglobin not readily associate with oxygen at a low partial pressure of oxygen?
Because the haem groups that attract an oxygen molecule are at the centre of the haemoglobin molecule It is difficult for the oxygen molecule to reach the haem group and associate with it
What relationship between % saturation with oxygen and partial pressure of oxygen would a normal liquid show?
Concentration absorbed by liquid is directly proportional
Why does a graph of % saturation with oxygen plotted against partial pressure in blood containing haemoglobin produce an S shape curve rather than a straight line?
Concentration of oxygen absorbed is not directly proportional to the oxygen tension of surrounding area because it is affected by how readily haemoglobin associates with oxygen
What occurs as the partial pressure of oxygen rises?
Diffusion gradient into haemoglobin molecule increases 1 oxygen molecules enters the haemoglobin molecule and associates with one of the haem groups This causes a conformational change in the haemoglobin molecule which allows more oxygen molecules to enter the haemoglobin molecule
How many oxygen molecules can a molecule of haemoglobin carry and why?
Each haem group can hold 1 oxygen molecule A haemoglobin molecule has 4 haem groups so can carry 4 oxygen molecules
Why does fetal haemoglobin have a higher affinity for oxygen than adult haemoglobin?
Fetal haemoglobin must be able to associate with oxygen in an environment where the oxygen tension is low enough to make the adult haemoglobin release oxygen
Where does the blood carry oxygen?
From lungs to heart before travelling around body to supply tissues
What occurs in the placenta so that the fetus receives oxygen from the mother?
In the placenta, oxygen tension is low, but still high enough for fetal haemoglobin to associate with it This reduces oxygen tension further, so oxygen diffuses from the mother's blood into the placenta fluid This reduces oxygen tension in the mother's blood causing the maternal haemoglobin to release more oxygen
What makes fetal haemoglobin different from adult haemoglobin?
It has a higher affinity for oxygen
How does the haemoglobin dissociation curve for fetal haemoglobin differ from the dissociation curve for adult haemoglobin?
It is to the left of adult haemoglobin
What are the needed conditions of oxygen tension in the placenta fluid and why?
Low enough oxygen tension for maternal haemoglobin to dissociate with oxygen High enough for fetal haemoglobin to associate with oxygen
Where in the body does haemoglobin associate with oxygen? Where in the body does oxyhaemoglobin dissociate from oxygen?
Oxygen binds to haemoglobin in the capillaries surrounding the alveoli, where the oxygen tension is high Oxygen dissociates from the haemoglobin in the capillaries of the tissues, where the oxygen tension is low
How is mammalian haemoglobin adapted to transport oxygen to tissues effectively?
Oxygen tension in lungs is sufficient to produce almost 100% saturation Oxygen tension in respiring tissues is low enough to cause oxygen to readily dissociate from oxyhaemoglobin
What is the partial pressure of oxygen (pO2)/ oxygen tension What does it measure? What unit is used to measure it?
Relative pressure that oxygen contributes to a mixture of gases Measures oxygen concentration kPa
What accounts for low saturation level of haemoglobin at low oxygen tensions?
The difficulty in combining with the first oxygen molecule because the haem group is at the centre of the haemoglobin molecule
Why is a steep concentration gradient of oxygen needed?
To allow oxygen to continue entering the blood from the lungs and diffuse into cells
How is a concentration gradient of oxygen maintained between blood from the lungs and blood from cells?
When oxygen becomes associated with haemoglobin, it takes the oxygen molecule out of solution which maintains a steep concentration gradient
What does the haem group contain?
a single iron ion in the form of Fe2+
What does the ability of haemoglobin being able to associate with/release oxygen depend on?
concentration of oxygen in the surrounding tissues
Define 'haemoglobin association curve'
curve that plots the proportion of hemoglobin in its oxygen saturated form against the oxygen tension
What is the structure haemoglobin?
globular protein 4 sub units each unit: polypeptide chain & a haem group (non protein group)
What happens to haemoglobin when it takes up oxygen
haemoglobin + oxygen -> oxyhaemoglobin
What causes the curve to level off in a % saturation vs partial pressure of oxygen graph
haemoglobin molecule approaching 100% saturation
What is oxygen transported in?
in haemoglobin molecules that are in red blood cells (erythrocytes)
What property of the haem group allows haemoglobin to carry oxygen?
iron ion has a high affinity for oxygen
What is dissociation?
oxyhaemoglobin releasing oxygen
Define haemoglobin
red pigment used to transport oxygen in the blood
What accounts for the steepness of the curve as oxygen tension rises?
the increase in gradient into the haemoglobin molecule causing 1 oxygen molecule to associate with a haem group causing a conformational change to the haemoglobin molecule which allows more oxygen molecules to enter the haemoglobin molecule, producing steepness