3.1.2 i and j transport of oxygen and carbon dioxide in the blood Flashcards
what are erythrocytes?
red blood cells
what are the adaptations of erythrocytes?
biconcave shape- larger sa so increase sa available for diffusion and helps them pass through narrow capillaries
no nuclei- maximises amount of haemoglobin that can fit into the cell
what is haemoglobin?
very large globular conjugated protein made up of four peptide chains each with an iron-contains haem prosthetic group
equation for oxygen binding to haemoglobin
Hb + 4O2 reversible reaction Hb(O2)4
what does oxygen binding to haemoglobin form?
oxyhaemoglobin
what is positive cooperativity?
as soon as one oxygen molecule binds to a haem group, the molecule changes shape which makes it easier for the next oxygen molecules to bind
how is a steep diffusion gradient maintained in the erythrocyte?
oxygen is bound to haemoglobin so the free oxygen concentration stays low so a diffusion gradient is maintained until all of the haemoglobin is saturated with oxygen
what happens with oxygen when blood reaches body tissues?
oxygen moves out of the erythrocytes down a concentration gradient
once first oxygen molecule is released, the molecule changes shape and it becomes easier to remove the remaining oxygen
what do we use an oxygen dissociation curve for?
understanding how blood carries and releases oxygen
what is plotted on an oxygen dissociation curve?
percentage saturation haemoglobin in the blood against the partial pressure of oxygen
what does a very small change in the partial pressure of oxygen in the surroundings do to the saturation of haemoglobin with oxygen?
makes a significant difference because once the first molecule becomes attached, the change in shape of the haemoglobin molecule means other oxygen molecules are added rapidly
what does it mean when the curve levels out on the oxygen dissociation curve?
highest partial pressures of oxygen because all the haem groups are bound to oxygen and so the haemoglobin is saturated and cannot take up anymore
what is the Bohr effect?
as the partial pressure of carbon dioxide rises, haemoglobin gives up oxygen more easily
why is the Bohr effect important?
in active tissues with a high partial pressure of carbon dioxide, haemoglobin gives up its oxygen more readily
in the lungs where the proportion of carbon dioxide in the air is relatively low, oxygen binds to haemoglobin molecules easily
why does fetal haemoglobin have a higher affinity for oxygen than adult haemoglobin?
because if both bloods had the same affinity than little or no oxygen would be transferred to the blood of the fetus
what are the three ways carbon dioxide is transported from the tissues to the lungs?
5% carried in the plasma
10-20% combined with amino groups in polypeptide chains of haemoglobin to form a compound called carbaminohaemoglobin
75-85% is converted into hydrogen carbonate ions in the cytoplasm of the red blood cell
what does carbon dioxide react with water to make?
carbonic acid
what happens when the carbonic acid dissociates?
forms hydrogen ions and hydrogen carbonate ions
what are there high levels of in the cytoplasm of the red blood cells?
carbonic anhydrase
what does carbonic anhydrase do?
catalyses the reversible reaction between carbon dioxide and water to form carbonic acid which dissociates
what do the hydrogen carbonate ions do?
move out of the cell into the plasma by diffusion down a concentration gradient and negatively charged chloride ions move into the cell which maintains the electrical balance of the cell
what is the chloride shift?
negatively charged hydrogen carbonate ions move out of the cell and negatively charged chloride ions move into the cell to maintain the electrical balance
what happens with carbon dioxide when the blood reaches the body tissues?
relatively low concentration of carbon dioxide
carbonic anhydrase catalyses reverse reaction breaking down carbonic acid into carbon dioxide and water
hydrogen carbonate ions diffuse back into red blood cells and react with hydrogen ions to form more carbonic acid
broken down into carbon dioxide which diffuses out of the blood
chloride ions diffuse out of red blood cells down the electrochemical gradient
how is haemoglobinic acid formed?
free hydrogen ions in a reversible reaction
what does haemoglobinic acid do?
acts as a buffer and prevents changes in the pH
