BYA7 SECTION 16.6Respiratory gases are transported between exchange surfaces and the individual cells of an organism |
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| The Transport of Respiratory Gases |
Haemoglobin and Hydrogen Carbonate Ions carry Respiratory Gases and Control Blood Ph |
| Haemoglobin Transports Oxygen |
- Lower atm pressure / fewer molecules present / less O2 reaches tissues
- Body adapts to changes by increasing
- Heart rate and resting breathing rate
- Blood plasma
- Red blood cell production and number of blood capillaries
- Haemoglobin Hb has 4 subunits, each subunit contains 2 parts
- Haem → ring of atoms linked to Fe2+
- Globin → polypeptide chain
- Sequence of amino acids affects O2 carrying properties
- Oxyhaemoglobin HbO2 from lungs dissociates in respiring tissues
- O2 diffuses into body cells while Hb is transported back to lungs
- Features of red blood cells that allow them to transport O2 more efficiently
- Biconcave disc → larger surface area to volume ratio for diffusion
- Absence of nuclei/other organelles → more room for haemoglobin
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Hydrogen Carbonate Ions Remove CO2 |
- CO2 produced in tissues diffuses into blood plasma
- There it reacts with H2O in the plasma and in the cytoplasm of red blood cells
- CO2 + H2O → H2CO3(carbonic acid) → H+ + HCO3- (hydrogen carbonate)
- In red blood cells, carbonic anhydrase is present
- Rate of HCO3- production is higher than in blood plasma
- Establishes a conc gradient → HCO3- diffuses into plasma
- Cl- diffuses into red blood cells to keep eqm in balance → chlorine shift
- \ Most CO2 is transported in blood as HCO3-
- But, small amount reacts directly with haem to produce carbamino-haem
- More CO2 binds to haem when O2 conc is low
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Control Of Blood pH |
- Dissociation of CO2 produces H+ ions
- Buffer keeps pH constant
- Plasma contains phosphate and
plasma proteins
- Red blood cells contain Hb
- Hb takes up H+ and releases O2 to respiring tissues
- H+ + HbO2 → Hb + O2
- The more H+ taken up by Hb the more O2is released
- Higher rate of respiration produces more CO2 from respiring tissues
- More H+ is produced and taken up by Hb
- More O2 is released \ more CO2 is transported in blood plasma
- Carbamino-haem travels to gas exchange surface
- There, more CO2 is removed and more O2 is taken up by haem
- More O2 is transported and supplied to respiring tissues
- \ CO2 regulates breathing rate
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The Oxyhaemoglobin Dissociation Curve |
- % saturation of Hb is plotted against partial pressure of O2 (pO2)
- pO2 is a measure O2 concentration
- 100% saturation of Hb → high partial pressure → in lungs
- Low pCO2 as it is removed from the body → high O2 uptake
- O2 is transported to and unloaded in tissues
- 60% saturation (straight line) in muscles → using up O2 carried by Hb
- S-shaped because each Hb carries 4 molecules of O2
- First molecule changes shape of Hb → remaining molecules bind more easily
- It becomes easier for the second and third molecules to bind
- Curve becomes flat at the end as binding of the last O2 is more difficult again
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The Bohr Effect |
- Increased pCO2
- moves dissociation curve to the right (Bohr shift)
- causes Hb to give up more O2 to respiring tissues
- pO2 falls (increase of respiration), more CO2 is released and rises pCO2
- Curve to the right of the normal for active animals
- Small animals → low surface area to volume ratio → readily lose heat
- Higher metabolism increases metabolic rate
- This requires more O2 for respiration to generate ATP
- pO2 is high at respiring tissues as it comes directly form lungs
- pCO2 must have a high value as well (see above)
- O2 is released at high pO2
- Curve to the left of the normal (greatest affinity for O2)
- pO2 is low in deep underground levels and high altitudes
- Fast release of O2 at low pO2 is required (Hb can adapt)
- Blood at placenta has low pO2
- Fetus lives in low pO2
- Fetal Hb has a high affinity for oxygen/is saturated at low pO2
- Mother gives up O2 and fetus picks it up
- Fetus takes up O2 in limited supply
- Red pigment myoglobin stores O2
- In muscles/anaerobic/diving animals → when O2 will get very low
- Fast release of O2 at very low pO2, but storage of O2 at high pO2 In some children fetal Hb is abnormally high / oxygen not released from fetal Hb/ in low pO2/body tissues/muscles / more
anaerobic respiration / less ATP available / muscle fatigue
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References and Further Reading
AQA (2006) GCE Biology/Biology (Human) 2006 specification, [PDF]
