Transport of 02 and CO2 in blood- transport in animals Flashcards
Adaptations of erythrocytes (red blood cells)
- biconcave shape= large SA=more diffusion and helps them pass through narrow capillaries
- no nuclei= max haemoglobin
erythrocytes
- red blood cells
- in adults, erythrocytes form in the red bone marrow. By the time mature (red blood cells) enter the circulation they have lost their nucleus=max haemoglobin but also limits their life(last120 days in the bloodstream)
haemoglobin
- red pigment
- carries O2
- Very large globular conjugated protein made up of four peptide chains, each with an iron containing prosthetic group
- 300 million haemoglobin molecules in each RBC and each haemoglobin molecule can bind to 4 02 molecules
- O2 binds quite loosely, forming oxyhaemoglobin (reversible reaction)
positive cooperativity
- the arrangement of haemoglobin molecule means as soon as 1 02 molecule binds to a haem group, the molecule changes shape, making it easier for next 02 to bind (reversed when blood meets body tissues)
- steep conc gradient maintained until all haemoglobin saturated with 02 because the free O2 concentration in erythrocyte stays low. (watch vid)
Describe conc gradient between alveoli and erythrocytes
-When erythrocytes enter capillaries in lungs, O2 levels in cell are low = steep conc gradient between inside of erythrocytes and air in alveoli
(this is reversed when blood reaches body tissues)
Describe how ppO2 changes with %saturation of haemoglobin
- at low PP, few haem groups are bound to O2=haemoglobin does not carry much
- at mid-high pp, more haem groups are bound to O2, making it easier for more O2 to be picked up
- at very high pp, haemoglobin becomes v saturated as all haem groups have become bound
Bohr effect
-as pp of CO2 rises, haemoglobin gives up O2 more easily
importance of bohr effect in the body
- in active tissue with high pp of CO2, haemoglobin gives up more O2 = more respiring
- in lungs where proportion of CO2 is low, O2 binds to haemoglobin more easily (watch vid)
how does fetal haemoglobin differ from adult?
Has a higher affinity for O2
-oxygenated blood from mother runs close to deoxygenated blood of fetus, so if had same affinity, the fetus would get little O2
3 different ways CO2 is transported from tissues to lungs
- 5% is carried dissolved in 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 red blood cells and transported to lungs
How are hydrogen carbonate ions formed
- carbon dioxide reacts slowly with water in blood plasma to form carbonic acid. The carbonic acid then dissociates to form hydrogen ions and hydrogen carbonate ions.
- in cytoplasm of RBC, there are high levels of the enzyme carbonic anhydrase which catalyses the reversible reaction between CO2 and water to form carbonic acid
chloride shift
-the negatively charged hydrogen ions formed by the dissociation of carbonic acid move out of the erythrocytes into the plasma by diffusion down a conc gradient and negatively charged chloride ions move into erythrocytes, which maintains electrical balance of the cell
how do RBC maintain steep conc gradient for CO2
- by converting CO2 into hydrogen carbonate ions
- therefore steep conc gradient for CO2 to diffuse into RBC
How is CO2 released back into lungs (reverse chloride shift)
- carbonic anhydrase catalyses the reverse reaction, breaking down carbonic acid into CO2 and water
- hydrogen carbonate ions diffuse back into erythrocytes and react with hydrogen ions to form more carbonic acid
- CO2 produced by breakdown of carbonic acid diffuses out of RBC into lungs
- chloride ions diffuse out of RBC into plasma to maintain electrochemical gradient
What role does haemoglobin play in chloride shift at lungs?
-acts as a buffer and prevents changes in pH by accepting free hydrogen ions in a reversible reaction to form haemoglobinic acid
