8.4- Transport Of Blood and Co2 In the Blood Flashcards
What is the equation of aerobic respiration ?
Glucose + oxygen —> carbon dioxide + water
What are the 3 ways that carbon dioxide can be transported in the blood ?
- dissolves directly in the blood plasma 5%
- carbaminohaemglobin in red blood cells 20%
- hydrogencarbonate ions in blood plasma 75%
Where is the carbon dioxide in aerobic respiration transported too ?
Transported from actively respiring tissues to the lungs where it is breathed out
What is the structure of carbaminohaemglobin ?
- contains 4 polypeptide chains
- the first amino acid has a free amino group
- each amino group reacts with a molecule of CO2
For every one molecule of Hb how many molecules of CO2 does it react with ?
4
What is the product when carbon dioxide reacts with haemoglobin ?
Carbaminohaemglobin
- this reaction is reversible go to good notes to see the equation *
What happens when blood passes through respiring tissue ?
- The levels of CO2 is increased
- Carbaminohaemglobin is formed
- however in the lungs the level of CO2 is low
- the carbaminohaemglobin breaks down releasing CO2
What is the product of carbon dioxide reacting with water ?
The compound carbonic acid in a reversible reaction
What is the name of the enzyme that red blood cells contain which speeds up this reaction ?
Carbonic anhydrase
Finish the sentence when carbon dioxide diffuses into red blood cells ….
It rapidly forms carbonic acid
Why is carbonic acid formed ?
- By converting carbon dioxide into carbonic acid this ensures the level of CO2 in the red blood cell is low
- thus meaning there is a steep concentration gradient for CO2
- due to the steep concentration gradient there is a higher rate of diffusion of carbon dioxide into the red blood cells
What happens once the carbonic acid is formed ?
It dissociates
State the equation for the dissociation of carbonic acid
H2CO3 —-> HCO3- + H+
<—
- go in good notes for a clearer equation *
Where is CO2 converted into HCO3- ions ?
Cytoplasm of the erythrocytes
Explain where the hydrogencarbinate ion diffuses out of and why ?
- diffuses out of the red blood cells to the blood plasma
What is meant by a charge imbalance ?
- Hydrogencarbonate ion has a negative charge
- when hydrogencarbonate ion diffuses out of the red blood cell this creates a charge imbalance as hydrogencarbonate has a negative charge
How do you prevent a charge inbalance ?
- hydrogencarbonate ion diffuses out of the red blood cell
- a negative chloride ion diffuses into the red blood cell
- this is called the chloride shift
What is the chloride shift ?
When the negatively charged hydrogencarbonate ions move out of the erythrocytes into the plasma by diffusion down a concentration gradient and negatively charged chloride ions move into the erythrocytes which maintains the electrical balance of the cell
What do the H+ ions cause ?
- the pH of the blood to fall
How do we prevent the pH of the blood to fall ?
Haemoglobin binds to the hydrogen ions and haemoglobin acts as a buffer
What is the product when Hb binds to hydrogen ions ?
Haemoglobinc acid
What happens when blood reaches the lung tissue where there is relatively low concentration of CO2 ?
- carbonic anhydrase catalyses the reverse reaction = breaking down the carbonic acid into carbon dioxide and water
- hydrogen carbonate ions diffuse back into the erythrocytes and react with hydrogen ions to form more carbonic acid
- when this is broken down by the carbonic anhydrase it reeks eases free carbon dioxide which diffuses out of the blood into the lungs
- chloride ions diffuse out of the red blood cells back into the plasma down an electrochemical gradient
Why does CO2 get converted into hydrogencarbonate ions in the red blood cells rather than in plasma ( more than in plasma ) ?
- reactions occurs more slowly in plasma
- high levels of enzyme carbonic anhydrase in red blood cells which catalyses the reversible reaction between carbon dioxide and water to form carbonic acid
- reaction occurs faster
What are erythrocytes main function ?
To transport O2
What are some adaptations of erythrocytes ?
- biconcave shape —> this shape has a larger SA than a simple disc structure or a sphere increasing the surface area available for diffusion of gases —> also helps them to pass through narrow capillaries
- no nuclei = maximises the amount of haemoglobin that fits into the cells
- contain haemoglobin
Where are erythrocytes continuously formed in adults ?
Red bone marrow
What do Hb and O2 react to form ?
Oxyhaemglobin
- go on good notes to see the full equation *
Explain what occurs when erythrocytes enter the capillaries in the lungs ?
- the O2 levels in the cells are relatively low
- this makes a steep concentration gradient between the inside of the erythrocytes and the air in the alveoli
- O2 moves into the erythrocytes and binds with the haemoglobin
- the arrangement of the Hb molecule means that 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
- this is known as positive cooperativity
- as the O2 is bound to the Hb the free O2 concentration in the erythrocytes stays low so a steep diffusion gradient is maintained until all of the Hb is saturated with oxygen
- when the blood reaches the body tissues - the situation is reversed
What happens when the concentration of oxygen in the cytoplasm of the body cells is lower than the erythrocytes ?
- O2 moves out of the erythrocytes down a concentration gradient
- once the first O2 molecule is released by the Hb the molecule again changes shape and it becomes easier to remove the remaining oxygen molecules
What is on the y axis of a O2 dissociation curve ?
% saturation of haemoglobin with O2
What is on the X axsis on the O2 dissociation curve ?
Partial pressure of O2
What does the O2 dissociation curve tell us about haemoglobin ?
- shows the affinity of haemoglobin for oxygen
- increase in the partial pressure of O2 = % saturation of Hb increases relatively slowly
- at around 4KPa of O2 = achieved 25% saturation each Hb molecule is bound to 1 O2 molecule on average
- at low partial pressures of O2 = Hb has low affinity for O2
- once 1 O2 molecule is bound the affinity of Hb for O2 increases and it is much easier to bind further O2 molecules
- at around 7KPa = 75% saturation and 2 more molecules have bound
What does affinity mean ?
How strongly the O2 is bound to the haemoglobin
What is in a molecule of Hb ?
- 4 poly peptide chains
- each polypeptide contains a haem group which can bind to O2
What happens if no O2 is bound ?
The haem group has a low affinity for O2 Molecules
What happens after the first O2 molecule bind to a haem group ?
- takes a relatively large partial pressure of O2 for the first O2 molecules to bind to a haem group
- when the 1st O2 molecule binds the quaternary structure of the Hb changes
- this increases the affinity of the haem groups for O2
- the 4th haem group only binds to O2 at a fairly high partial pressure because 3/4 of the haem groups have already been bound so the chances of O2 molecules colliding with the 4th haem group is relatively low
What is positive cooperativity ?
As soon as one oxygen molecule binds to a haem group the haemoglobin molecule changes shape making it easier for the next molecules to bind
Why does an oxygen dissociation curve level off at the end ?
Because all the haemoglobin is saturated
What are the effects of CO2 on the oxygen dissociation curve ?
- in active tissues with a high partial pressure of carbon dioxide haemoglobin gives up Ute oxygen more rapidly
- in the lungs where the proportion of carbon dioxide in the air is relatively low oxygen binds to the haemoglobin molecules easily
- causes a shift in the whole oxygen dissociation curve to the right
= thus meaning that CO2 causes the oxygen affinity of haemoglobin to decrease
What did the Bohr effect do to an oxygen dissociation curve ?
Shift it to the right
What are the two important effects of bohrs effect ?
- Hb has a higher affinity for oxygen
- in conditions where the partial pressure of CO2 is low for eg. In the lungs = Hb has a high level of O2 saturation
- however the partial pressure of CO2 will be high in active tissues undergoing aerobic respiration as the Hb has a lower O2 affinity it is much more likely to unload it’s bound oxygen in these tissues
What occurs when a fetus is developing in the uterus in regards to its supply of oxygen ?
- completely dependent on its mother to supply it with oxygen
- oxygenated blood from the mother runs close to the deoxygenated fetal blood in the placenta
- they do not mix
What is the difference between feral and adult haemoglobin ?
Feral Hb has a higher affinity for O2
Why is there a difference in the Hb in adults and fetus ?
If a mother and the fetus had the same affinity for oxygen little or no oxygen would be transferred to the blood of the fetus and the fetus would not get enough oxygen
Does fetal Hb have a higher or lower affinity for oxygen than adult haemoglobin and explain why ?
Fetal Hb has a higher affinity for oxygen than adult haemoglobin at each point along the dissociation curve
How does the oxygen dissociation curve for foetal Hb differ to an adults Hb ?
Shifted to the left
What would happen if fetal Hb had a very high O2 affinity ?
Could prevent it from unloading O2 to the fetal tissues therefore the O2 affinity of fetal Hb is only slightly greater than the adult
What is the difference between the way in which carbon dioxide and oxygen bind to Hb ?
CO2 binds with amino acids in Hb
O2 binds with iron ions in the prosthetic group
Why is the oxygen dissociation curve sigmoidal ?
- shallow at start because it’s relatively difficult for first O2 to bind
- Hb changes shape and this makes I easier for the 2nd and 3rd molecules to bind steepening the curve
- 4th oxygen is difficult to add so shallow again
What does partial pressure mean ?
The relative pressure a gas contributes to a mixture of gases in KPa
What is partial pressure also referred as ?
Oxygen tension
What is Hb ?
A large conjugated protein
