transport of oxygen Flashcards
meaning of affinity
a strong attraction
meaning of disocciation
releasing the oxygen from the haemoglobin
fetal haemoglobin
type of haemoglobin usually found in the foetus
haemoglobin
red pigment used to tranport oxygen in the blood
what is the most specialised transport role of the blood
to transport oxygen from the lungs to the cells of the body by erythrocytes
what is the blood also involved in
the removal of carbon dioxide from the cells and its transport to the lungs for gas exchange
why do rbc have a flattened, biconcave disc shape
increases the surface area available for diffusion of gases. helps them pass through narrow capillaries
why is the diameter of the rbc larger than the diameter of a capillary
slows blood flow enabling diffusion of oxygen
why do rbc have a lot of haemoglobin
for transporting oxygen
why dont rbc have a nucleus or other organelles
maximises the space available for haemoglobin so more oxygen can be transported
where are erythrocytes formed in adults
red bone marrow
what happens by the time erythrocytes enter the circulation
they have lost their nucleus maximising the amount of haemoglobin that fits into the cells. it also limits their life so they only last for 120 days in the bloodstream
what is the diameter of an erythrocyte
6-8µm
why is the haemoglobin close to the plasma membrane
so the oxygen is loaded and unloaded very quickly in and out of the cell
what do the narrow capillaries (6µm) allow red blood cells to do
pass through one at a time increasing surface area for gas exchange. this slow single file flow maximises oxygen delivery to tissues and improves carbon dioxide removal
what does the close contact between red blood cells and capillary cells enhance
nutrient and waste exchange.
how else is gas exchange optimised in the capillaries
the red blood cells deform optimising gas exchange
what is haemoglobin
a large globular conjugated protein. it is a red pigment that gives the red blood cells their colour
describe the structure of haemoglobin
made of four peptide chains each with an iron containing prosthetic group called haem
what does the haem group do
it contains a single iron ion in the form of Fe2+. this iron ion can attract and hold one oxygen molecule.
what does the haem group have a high affinity for
oxygen
how many oxygen molecules can haemoglobin carry
4
how many haemoglobin molecules are there in each red blood cells
300 million
how does haemoglobin form oxyhaemoglobin
at partial pressures of oxygen the haemoglobin will bind forming oxyhaemoglobin
what is the saturation of haemoglobin measured in
%
fully saturated =…
100%
equation for the formation of oxyhaemoglobin
Hb + 4O2 —–> Hb(O2)4
haemoglobin + oxygen —-> oxyhaemoglobin
how are the oxygen levels like when the erythrocytes first enter the capillaries in the lungs
the oxygen levels in the cells are relatively low
how is a steep concentration gradient maintained between the inside of the erythrocytes and the air in the alveoli
when the erythrocytes first enter the capillaries in the lungs, the oxygen levels in the red blood cells are relatively low. this allows oxygen to move in and bind with haemoglobin
how are the haemoglobin molecules arranged
as soon as one oxygen molecule binds to a haem group the molecule changes shape making it easier for the next oxygen molecules to bind
what is positive cooperativity
If the change in shape of the first subunit makes easier the binding of substrate to the second subunit,
why does the free oxygen concentration stay low after the binding of haemoglobin
because the oxygen is bound to the haemoglobin, the free oxygen concentration in the erythrocyte stays low, so a steep diffusion gradient is maintained until all of the haemoglobin is saturated with oxygen
what happens when the blood reaches the body tissue
the concentration of oxygen in the cytoplasm of the body cells is lower than in the erythrocytes. oxygen moves out of the erythrocytes down a concentration gradient
what happens when the 1st oxygen molecule is released by the haemoglobin
the molecule changes shape and it becomes easier to remove the remaining oxygen molecule
what happens as each oxygen molecules binds
it alters the conformation of haemoglobin, making subsequent binding easier. oxygen will have a higher affinity for oxygen in oxygen rich areas (like the lungs) promoting oxygen loading
haemoglobin will have a lower affinity for oxygen in oxygen starved areas (like the muscles) promoting oxygen unloading
when does oxygen bind to haemoglobin
when oxygen is at a high concentration
when does oxygen dissociate from haemoglobin
when oxygen is at a low concentration
how can the concentration of a gas in a mixture can be quantified in terms of
its partial pressure
what is partial pressure
the amount of pressure exerted by the gas relative to the total pressure exerted by all the gases in the mixture
what is partial pressure measured in and written as
kPa and written as P(O2) and P(CO2)
what is the oxygen dissociation curve
graph that shows the % concentration of haemoglobin at various partial pressures of oxygen. shows how blood carries and releases oxygen
what happens to the curve at low partial pressures
ratio of oxyhaemoglobin to haemoglobin is correspondingly low. most haemoglobin molecules will only take up one oxygen molecule or none at all
what happens to the curve as the graph gets steeper
once a haemoglobin molecule has picked up one oxygen molecule its oxygen affinity increases. a small increase in oxygen availability leads to a large increase in saturation. once the first molecule attaches the change in the shape of the haemoglobin molecules means other oxygen molecules are added rapidly
what happens to the curve once the graph reaches the top
once a high saturation has reached (the haemoglobin is fully saturated with oxygen) some molecules will be unable to take on any more oxygen. further rises in pressure makes less difference to the saturation and the graph levels out
why is oxygen rapidly loaded in the lungs
the oxygen partial pressure is high so most haemoglobin becomes saturated with oxygen. (95-97% saturated)
why is oxygen rapidly released at respiring tissue
partial pressure is low so haemoglobin loses oxygen to only 20-25% saturation
what happens when you aren’t active
only about 25% of the oxygen carried in your erythrocytes is released into the body cells. the rest acts as a reservoir for when the demands of the body suddenly increase suddenly
what is the bohr effect
describes the effect that an increase in carbon dioxide has on the haemoglobin explaining the release of more oxygen.
what does the oxygen affinity of haemoglobin depend on besides its saturation
physical and chemical factors such as pH and temperature
what does an increase in CO2 in a tissue during exercise do
lowers its pH. this lowers the oxygen affinity over all partial pressures leading to increased release of oxygen where it is needed
what does the Bohr shift do
allows the haemoglobin to give up oxygen more readily
when will oxygen bind to the haemoglobin molecules easily
in the lungs where the proportion of carbon dioxide in the air is relatively low
where does the curve shift if there is low CO2
left
where does the curve shift if there is high CO2
right
what does an increased temperature do the affinity of haemoglobin
decreases the affinity
as oxyhaemoglobin is exposed to higher temperatures in the metabolising tissues, affinity decreases and haemoglobin unloads oxygen
what does a decrease in temperature do the affinity of haemoglobin
increases haemoglobins oxygen affinity slightly. hypothermia reduces the bloods ability to release oxygen into the metabolising tissue
what is fetal haemoglobin
haemoglobin in the red blood cells of the foetal blood stream
what is fetus dependant on
the mother to supply it with oxygen
how does the mother supply the fetus with oxygen
oxygenated blood from the mother runs close to the deoxygenated blood in the placenta
what would happen if the blood of the fetus has the same affinity for oxygen as the blood of the mother
then little or no oxygen would be transferred to the blood of the foetus
what is the affinity for oxygen in fetal haemoglobin
slightly higher (curve is towards left)
why is fetal haemoglobins affinity higher
fetal haemoglobin must be able to associate with oxygen in an environment where the oxygen tension is low enough to make adult haemoglobin release oxygen
what is the partial pressure of oxygen in the placenta
low
how does oxygen reach the foetus
in the placenta the oxygen tension is low (partial pressure). fetal haemoglobin will absorb oxygen from the surrounding fluid which reduces oxygen tension even more. oxygen diffuses from the mothers blood into the placenta. this reduces oxygen tension within the mothers blood making the maternal haemoglobin release more oxygen (dissociation)
what is myoglobin
a molecule similar to haemoglobin with only one haem group
what is the affinity of myoglobin for oxygen
has a high affinity even at low partial pressures
when does oxymyoglobin dissociate
when oxygen levels are low
where is myoglobin found
in muscle cells where it acts as a reserve
where is the curve for myoglobin
slightly to the left and higher
