Heart, Hb etc Flashcards
The cardiac cycle
ask
The ventricles relax whilst the atria contract.
- the contraction of the atria means a decrease in volume but an increase in the pressure. Because the ventricles at this moment are relaxed, the pressure in the atria exceeds the pressure in the ventricles so blood is pushed into the ventricles.
- there is a small increases in ventricular pressure and chamber volume as the ventricles receive the blood being ejected from the contracting atria
The ventricles contract whilst the atria relax
- the contraction of the ventricles means that chamber volume decreases but there is an increase in pressure. The pressure in the ventricles becomes higher than the pressure in the atria so the atrioventricular valves (tricuspid and bicuspid) are forced shut, preventing the back flow of blood.
- the pressure in the ventricles is higher than the pressure in the aorta (pathways after left ventricle) and pulmonary artery (pathway after right ventricle) so the semi lunar valves are forced open and blood flows into the aforementioned arteries.
The ventricles and atria both relax
- there is a higher pressure in the pulmonary artery and the aorta than in the ventricles (which are now relaxed) so the semi lunar valves are forced shut, preventing the back flow of blood into the ventricles.
- the blood flows out to the body (some to the body if it’s had its second pump and some to the lungs to get oxygenated if it still needs to return to the heart for its second pump)
- the blood returns to the heart and because there is a higher pressure in the vena cava and pulmonary vein (where blood is entering back into the heart from) than in the atria, it means that blood flows into the atria and they begin to fill again. This increases atrial pressure.
- whilst all this is happening the ventricles are still relaxing and as they relax their pressure falls until it becomes lower than the pressure in the atria which means that the atrioventricular valves open and blood flows passively into the ventricles from the atria.
- the process starts again so as I said before at the top of this flashcard, the atria contract (decreasing volume but increasing pressure) to squeeze the last bit of blood into the ventricles. CHECK: I don’t get it because the top of the flashcard is about blood flowing into the atria because of contracts and pressure but here it says that blood flows in passively when the process repeats???
MAYBE: the end of the process is passive when like as much blood is entering the ventricles as it passively can but the process restarts when the atria contract to push the blood that can’t passively flow into the ventricles!?
What has haemoglobin evolved to be like? (In terms of efficiency)
Efficient at loading oxygen in one se of conditions
Efficient at unloading oxygen in another set of conditions
Describe the structure of a haemoglobin molecule. (In terms of primary, secondary etc)
Primary - sequence of amino acids in 4 chains
Secondary - polypeptide chain folded into alpha helices and beta pleated sheets
Tertiary - polypeptide chain further folded into a precise shape
Quaternary - all 4 polypeptide chains linked together to form a spherical molecule.
What is each polypeptide chain of haemoglobin associated with?
Each polypeptide chain associated with a haem group that contains an Fe 2+ ion
Each Fe 2+ carries an oxygen
So each haemoglobin carries 4 oxygen molecules
What does the gene group allow haemoglobin to do?
Bind to oxygen
Haemoglobin bonding to oxygen is called
Loading or associating
Takes place in the lungs
Haemoglobin releasing oxygen is called
Unloading or dissociating
This takes place in the tissues
What does Hb with a high affinity for oxygen do?
Takes up oxygen more easily but releases it less easily
What does Hb with a low affinity for oxygen do
Takes up oxygen less easily but releases it more easily
How must Hb be efficient at the surface where gas exchange is occurring? (2)
- readily associate with oxygen at the surface where gas exchange takes place
- readily dissociate with oxygen at the tissues requiring oxygen
What is the important property of haemoglobin?
Give an example of what happens in a particular condition
It changes its affinity (chemical attraction) to oxygen under different conditions.
It does this by changing it’s shape in the certain conditions.
When there is lots of carbon dioxide the shape changes so that the Hb molecule binds more loosely to oxygen and as a result Hb LOSES (unloads) it’s oxygen
At the respiring tissues …. (oxygen conc, carbon dioxide conc, affinity of Hb for oxygen)
Oxygen conc is low
Carbon dioxide conc is high
So Hb has lower affinity for oxygen so it unloads oxygen
At the lungs gas exchange surface …. (oxygen conc, carbon dioxide conc, affinity of Hb for oxygen)
Oxygen conc is high
Carbon dioxide conc is low
Hb has high affinity for oxygen so oxygen loads on
What tends to differ about different organisms haemoglobin?
Haemoglobins have different affinities for oxygen
Why do different haemoglobin have different affinities for oxygen?
It’s due to the shape of the haemoglobin molecule
—> each haemoglobin has a slightly different tertiary and therefore quaternary structure so different oxygen binding properties. Depending on the structure of the Hb molecule they range from those with a high affinity for oxygen to those with a low affinity for oxygen.
At the respiring tissues …. (oxygen partial pressure, affinity of Hb for oxygen, Hb saturation)
Oxygen partial pressure is low
Hb affinity for oxygen is low
Hb saturation is low
At the lungs …. (oxygen partial pressure, affinity of Hb for oxygen, Hb saturation)
Oxygen partial pressure is high
Hb affinity for oxygen is high
Hb saturation is high
What does an oxygen dissociation curve show?
Relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen
Describe the first part of the sigmoid oxygen dissociation curve
Shape of the Hb molecules makes it difficult for the first oxygen molecule to bind to one of the (Fe 2+?) in the heme group of one of the polypeptide chains (why?) because the chains are so closely united
At low oxygen concentrations little oxygen binds to haemoglobin.
Curve gradient is shallow
What does the binding of the first oxygen molecule to Hb mean?
Binding of first oxygen molecule changes the quaternary structure of the haemoglobin causing it to change shape. This change in shape makes it easier for the other sub units to bind to an oxygen molecule
Gradient of the curve steepens
(Hb alters it’s shape into the relaxed R state that has a higher affinity for oxygen)
Define positive cooperativity
Binding of the second oxygen molecule makes it easier for other subunits to bind more easily to an oxygen molecule
What does it mean for the increase in partial pressure of oxygen once the first oxygen molecule has bonded to Hb
It takes a smaller increase in partial pressure of oxygen for the second oxygen molecule to bind than it did for the first one.
First oxygen molecule binds after partial pressure of oxygen has increased a bit then because this alters shape of Hb partial pressure of oxygen doesn’t have to change much more until it becomes easier for the second oxygen molecule to bind
Describe how binding of the last oxygen molecule is affected by the binding of the third to Hb?
Binding of the fourth oxygen molecule is harder due to probability. Majority of binding sits occupied means it is less likely the oxygen will locate the last empty site to bind to.
Gradient goes to zero as curve flattens off but never fully reaches 100% Hb saturation
What does it mean if the oxygen dissociation curve is further to the LEFT
The greater the affinity of haemoglobin for oxygen
[loads oxygen more easily but unloads oxygen less readily]
(because Hb starts loading oxygen at lower oxygen partial pressures)
What does it mean if the oxygen dissociation curve is further to the RIGHT
The lower the affinity of Hb for oxygen
[loads oxygen less readily but unloads more easily]
(Because the Hb starts loading oxygen and saturation starts increasing only at higher oxygen partial pressures)
What does steep mean on the oxygen dissociation curve?
Loading of oxygen is easier
Unloading of oxygen is easier
What do shallow parts of the haemoglobin dissociation curve mean?
Harder for oxygen to bind
?what does it mean for unloading?
Harder for oxygen to unload because less carbon dioxide ?
What happens to the curve of oxygen affinity of Hb increases
Shifts left
Loading increases and obvs unloading decreases so less delivery of oxygen per gram of Hb
What causes increased affinity in Hb molecule?
A conformational or structural change in the Hb molecule
Usually eg. Brought about by first oxygen binding
What is the prosthetic group in haemoglobin?
Heme group
(Protoporphyrin ring with an Fe 2+ in the centre)
Fe 2+ has 4 single bonded nitrogen’s coming off and two of these nitrogens each have a double bond carbon and single bond carbon and the other two have both single bond carbon
Where EXACTLY does oxygen bind to haemoglobin ?
The Fe 2+ in the heme group.
Describe the relationship between O2 partial pressures and haemoglobin saturation.
Positive correlation
As partial pressure of oxygen increases the Hb saturation also increases
Describe the relationship between carbon dioxide partial pressure and haemoglobin affinity
Négative corrélation
As carbon dioxide partial pressure increases the affinity of Hb decreases
What two things mean oxygen is readily loaded onto Hb at the lungs?
Low carbon dioxide partial pressures (so doesn’t reduce affinity of Hb)
High oxygen partial pressures
Which way does the oxygen dissociation curve shift when carbon dioxide partial pressures Decrease
Left
Hb still has high affinity for oxygen
What two things mean oxygen is readily unloaded from Hb at te repairing tissues?
High carbon dioxide partial pressures (decreases affinity of Hb for oxygen)
Low oxygen partial pressures
Which way does the curve shift when carbon dioxide partial pressure increases ?
Right
Hb has lower affinity for oxygen so takes higher partial pressure for Hb to start becoming saturated
What are the normal axis for an oxygen dissociation curve?
Y axis - Hb affinity/saturation
X axis - oxygen partial pressure
What’s the difference between oxygen partial pressure and oxygen concentration of the X axis?
X
What happens if the carbon dioxide partial pressure is on the x axis?
X
How does low pH cause Hb to have a lower affinity for oxygen?
X
How does affinity of Hb for carbon monoxide work?
X
Explain what happens with Hb affinity at the lungs.
Carbon dioxide constantly removes so pH slightly raised (less H+ ions)
Higher pH alters shape of Hb so it loads oxygen more readily
Shape therefore increases Hb affinity for oxygen (also means it isn’t released whilst being transported through the blood to the tissues)
Explain what happens with Hb affinity at respiring cells
At respiring cells there is lots of carbon dioxide
Carbon dioxide dissolves to form carbonic acid which decreases pH of blood within tissues
Lower pH changes shape of Hb so it unloads oxygen more readily
Shape therefore decreases Hb affinity for oxygen and oxygen is unloaded into repairing cells
Explain the sequence of events to show how lots of oxygen is provided when cells respire a lot
Higher rate of respiration
More CO2
Lower pH
Greater Hb change in shape
Greater Hb affinity for oxygen decreases
More readily oxygen is unloaded
More oxygen available for respiration
How much oxygen is unloaded by Hb at tissues of low respiratory rates and what is Hb returning to the lungs like?
When it reaches a tissue with only a LOW RESPIRATORY RATE (so requires less oxygen) it unloads one oxygen molecule only.
The blood returning to the lungs still contains Hb which is quite saturated.
What is the normal saturation of Hb?
97% Hb loaded with oxygen at atmospheric pressures