Haemoglobin and Cardiac cycles Flashcards
Structure of haemoglobin:
-is a globular protein which is an O2-carrying pigment found in vast quantities in red blood cells - biconcave no nucleus
-Haemoglobin has a quaternary structure as it’s made up of 4 polypeptide chains
-these chains are globin proteins (2 alpha and 2 beta globin’s) and each subunit has a prophetic haem group
-the 4 globin subunits are held together by disulphide bonds, hydrophobic R groups facing inwards to maintain shape and hydrophilic R groups facing outwards to maintain solubility
-the haem group contains iron II ions which is able to reversibly combine with an oxygen molecule forming oxyhaemoglobin
-each haem group is therefore able to carry 4 oxygen molecules or 8 oxygen atoms
-the haem group is the same for all types of haemoglobin but chains can differ between different species
Haemoglobin function:
-responsible for binding to oxygen in the lungs and transporting the O2 to the tissues to be used in aerobic respiration
-as O2 isn’t very soluble in water and haem is, O2 can be carries more efficiently around the body when bound to the haemoglobin
-the existence of Fe2+ in the prosthetic haem group allows O2 to reversibly bind
The role of Haemoglobin:
the majority of O2 transported around the body is bound to the protein haemoglobin in RBC aka erythrocytes
each molecule of haemoglobin contains 4 haem groups, each able to bond with 1 molecule of oxygen
4O2 + Hb = Hb4O2
the binding of the first oxygen molecules results in a conformational change in the structure of haemoglobin molecule making it easier for each successive oxygen molecule this is co-operative binding
the reverse of this process happens when oxygen disassociates in the tissues
volume and pressure changes:
-contraction of the heart muscle causes a decrease in volume in the corresponding chamber of the heart which then increases again when the muscle relaxes
-volume changes lead to corresponding pressure changes - volume decrease = pressure increases and when volume increases = pressure decreases
valves open when the pressure of the blood behind them is greater than in front and they close when the pressure in front of them is greater than behind
atrial systole:
-the wall of the atria contract atrial volume decreases so pressure increases
-the pressure in the atria rises above that in the ventricles forcing the atrioventricular valves to open
-blood is forced into the ventricles there is a slight increase in ventricular pressure and chamber volume as the ventricles receive blood from the atria
-the ventricles are relaxed at this point; ventricular diastole coincides with atrial systole
ventricular systole:
-the walls of the ventricles contract ventricular volume decreases and pressure increases
-the pressure in the ventricles rises above that in the atria this forces the atrioventricular valve to close preventing back flow
-the pressure in the ventricles rises above that in the aorta and pulmonary artery this forces the semilunar valves open so blood is forced into the arteries and out of the heart
-during this period the atria are relaxed; atrial diastole coincides with ventricular systole
Diasole:
-the atria and ventricles are both relaxed
-the pressure in the ventricles drops below that in the aorta and pulmonary artery forcing the semilunar valves close
-the atria continue to fill with blood
-pressure in the atria rises above that in the ventricles forcing the atrioventricular valves open
-blood flows passively onto the ventricles without need of atrial systole
-the cycle then begins again with atrial systole
analysing the cardiac cycle:
-the points at which the curves cross over each other are important because they indicate when valves open and close
-point A: pressure sits at roughly 0KPa
-between points A and B: atrial systole - left atria contracts and empties blood into left ventricle
-point B: beginning of ventricular systole - left ventricle pressure increases AV valve shuts, pressure in the left atria drops as the left atrium expands
-point C: pressure in the left ventricle exceeds that in the aorta - aortic valve opens and blood enters the aorta
-point D: left ventricle has been empties of blood muscles in the walls of the left ventricle relax and pressure falls below that in the aorta aortic valve closes AV valve opens
point E: expansion of the left ventricle - this is a short period of time during which the left ventricle expands this increases the internal volume of the left ventricle which decreases the pressure
the Bohr shift:
changes in the oxygen dissociation curve as a result of carbon dioxide levels
what happens when the partial pressure of CO2 is high?
haemoglobin affinity for oxygen is reduced this is a helpful change because it means that haemoglobin gives up its oxygen more readily in the respiring tissues where it’s needed
different types of haemoglobin:
-haemoglobin is a quaternary protein made up of 4 globin polypeptides and 4 haem groups
-the structure of haem is identical in all types of haemoglobin but the globing chains can differ between species
-haemoglobin types vary in their oxygen-binding properties meaning that they bind to and release oxygen in different conditions
-environmental factors can have a major impact on the evolution of haemoglobin within a species
effects of alltitude:
-the partial pressure of oxygen in the air is lower at higher altitudes
-species living at high altitudes have a haemoglobin that is adapted to these conditions
foetal haemoglobin:
-the haemoglobin of a developing foetus has a higher affinity for oxygen than adult haemoglobin
-this is vital as it allows a foetus to obtain oxygen form its mothers’ blood at the placenta
-on a disassociation curve graph the curve for foetal haemoglobin shift to the left of that for adult haemoglobin
-after birth a baby begins to produce adult haemoglobin which gradually replaces foetal haemoglobin
analysing the cardiac cycle part 2:
point a - the end of diastole: the atrium has filled with blood during the preceding diastole, pressure is higher in the atrium that in the ventricle so the AV valve is open
between a and b - atrial systole: left atrium contracts causing an increase in arterial pressure forcing blood into the left ventricle, ventricular pressure increases slightly as it fills with blood, pressure is higher in the atrium than in the ventricle so the AV valve is open
point b - beginning of ventricular systole: left ventricle contracts causing the ventricular pressure to increase, pressure in the left atrium drops as the muscle relaxes, pressure in the ventricle exceeds pressure in the atrium so the AV valve shuts
point c - ventricular systole: the ventricle continues to contract, pressure in the ventricles exceeds that in the aorta, aortic valve open and blood is forced into the aorta
point d - beginning of diastole: left ventricle has been emptied of blood, muscles in the wall of the left ventricle and pressure falls below that in the newly filled aorta, aortic valve closes
between d and e - early diastole: the ventricle remains relaxed and ventricular pressure continues to decrease, in the meantime blood is flowing into the relaxed atrium from the pulmonary vein causing an increase in pressure
point e - diastole: the relaxed left atrium fills with blood causing the pressure in the atrium exceed that in the newly emptied ventricle, AV valve opens
after point e - late diastole: there is a short period of time during which the left ventricle expands due to relaxing muscles, this increases the internal volume of the left ventricle and decreases the ventricular pressure, at the same time blood is flowing slowly through the newly opened AV valve into the ventricle causing a brief decrease in pressure in the left atrium, the pressure in both the atrium and ventricle ten increases slowly as they continue to fill with blood
what is the disassociation curve:
shows the rate at which oxygen associates and disassociates with haemoglobin at different partial pressure of oxygen
explain the shape of the curve:
-due to the shape of haemoglobin molecules it’s difficult for the first oxygen molecule to bind to haemoglobin which means this binding of oxygen occurs slowly resulting in a shallow curve at the bottom left corner of the graph
-after the first oxygen molecule binds to the haemoglobin the haemoglobin protein changes shape making it easier for the next oxygen molecule to bind this speeds up binding of the remaining oxygen molecules which results the steeper art of the curve in the middle of the graph - as shape changes of haemoglobin is called cooperative binding
-as the molecule of haemoglobin approaches saturation it takes longer for the 4th oxygen molecule to bind due to shortage of remaining binding sites resulting the levelling off of the curve in the top right corner of the graph
interoperating the curve:
-when the curve is read form left to right it provides information about the rate at which haemoglobin binds to oxygen at different partial pressures of oxygen
-when read form right to left the curve provides information about the rate at which haemoglobin disassociates with oxygen at different partial pressures of oxygen
