D.6 Gas Transport
Essential idea:
Red blood cells are vital in the transport of respiratory gases.Understandings:
Understandings
D.6 U 1 Oxygen dissociation curves show the affinity of hemoglobin for oxygen.
D.6 U 2 Carbon dioxide is carried in solution and bound to hemoglobin in the blood.
D.6 U 3 Carbon dioxide is transformed in red blood cells into hydrogen carbonate ions.
D.6 U 4 The Bohr shift explains the increased release of oxygen by hemoglobin in respiring tissues.
D.6 U 5 Chemoreceptors are sensitive to changes in blood pH.
D.6 U 6 The rate of ventilation is controlled by the respiratory control centre in the medulla oblongata
D.6 U 7 During exercise the rate of ventilation changes in response to the amount of CO2 in the blood.
Applications
D.6.A1 Consequences of high altitude on gas exchange
D.6.A2 pH of Blood is regulated to stay within the narrow range of 7.35 to 7.45
D.6 A 3 Causes and treatments of emphysema.
Skills
D.6 S 2 Identification of pneumocytes, capillary endothelium cells and blood cells in light micrographs and electron micrographs of lung tissue.
D.6 S 1 Analysis of dissociation curves for hemoglobin and myoglobin.
Red blood cells are vital in the transport of respiratory gases.Understandings:
Understandings
D.6 U 1 Oxygen dissociation curves show the affinity of hemoglobin for oxygen.
D.6 U 2 Carbon dioxide is carried in solution and bound to hemoglobin in the blood.
D.6 U 3 Carbon dioxide is transformed in red blood cells into hydrogen carbonate ions.
D.6 U 4 The Bohr shift explains the increased release of oxygen by hemoglobin in respiring tissues.
D.6 U 5 Chemoreceptors are sensitive to changes in blood pH.
D.6 U 6 The rate of ventilation is controlled by the respiratory control centre in the medulla oblongata
D.6 U 7 During exercise the rate of ventilation changes in response to the amount of CO2 in the blood.
Applications
D.6.A1 Consequences of high altitude on gas exchange
D.6.A2 pH of Blood is regulated to stay within the narrow range of 7.35 to 7.45
D.6 A 3 Causes and treatments of emphysema.
Skills
D.6 S 2 Identification of pneumocytes, capillary endothelium cells and blood cells in light micrographs and electron micrographs of lung tissue.
D.6 S 1 Analysis of dissociation curves for hemoglobin and myoglobin.
QUICK REVIEW ON HEMOGLOBIN
D.6.U1 Oxygen dissociation curves show the affinity of hemoglobin for oxygen
Oxygen dissociation curves show the relationship between oxygen levels (as partial pressure) and haemoglobin saturation
Oxygen dissociation curves show the relationship between oxygen levels (as partial pressure) and haemoglobin saturation
- Because binding potential changes with each additional O2 molecule, the saturation of haemoglobin is not linear
- The oxygen dissociation curve for adult haemoglobin is sigmoidal (i.e. S-shaped) due to cooperative binding
- There is a low saturation of haemoglobin when oxygen levels are low (haemoglobin releases O2 in hypoxic tissues)
- There is a high saturation of haemoglobin when oxygen levels are high (haemoglobin binds O2 in oxygen-rich tissues)
D.6 U 2 Carbon dioxide is carried in solution and bound to hemoglobin in the blood.
D.6 U 3 Carbon dioxide is transformed in red blood cells into hydrogencarbonate ions.
Carbon dioxide is transported between the lungs and the tissues by one of three mechanisms:
Carbon Dioxide Transport in the Bloodstream
D.6 U 3 Carbon dioxide is transformed in red blood cells into hydrogencarbonate ions.
Carbon dioxide is transported between the lungs and the tissues by one of three mechanisms:
- Some is bound to haemoglobin to form HbCO2 (carbon dioxide binds to the globin and so doesn’t compete with O2 binding)
- A very small fraction gets dissolved in water and is carried in solution (~5% – carbon dioxide dissolves poorly in water)
- The majority (~75%) diffuses into the erythrocyte and gets converted into carbonic acid
- When CO2 enters the erythrocyte, it combines with water to form carbonic acid (reaction catalysed by carbonic anhydrase)
- The carbonic acid (H2CO3) then dissociates to form hydrogen ions (H+) and bicarbonate (HCO3–)
- Bicarbonate is pumped out of the cell in exchange with chloride ions (exchange ensures the erythrocyte remains uncharged)
- The bicarbonate in the blood plasma combines with sodium to form sodium bicarbonate (NaHCO3), which travels to the lungs
- The hydrogen ions within the erythrocyte make the environment less alkaline, causing haemoglobin to release its oxygen
- The haemoglobin absorbs the H+ ions and acts as a buffer to maintain the intracellular pH
- When the red blood cell reaches the lungs, bicarbonate is pumped back into the cell and the entire process is reversed
Carbon Dioxide Transport in the Bloodstream
D.6.U4 The Bohr shift explains the increased release of oxygen by hemoglobin in respiring cells
D.6.U5 Chemoreceptors are sensitive to changes in blood pH
Respiratory chemoreceptors work by sensing the pH of their environment through the concentration of hydrogen ions. Because most carbon dioxide is converted to carbonic acid (and bicarbonate ) in the bloodstream, chemoreceptors are able to use blood pH as a way to measure the carbon dioxide levels of the bloodstream.
The main chemoreceptors involved in respiratory feedback are central chemoreceptors and Peripheral chemoreceptors:
Central chemoreceptors:
Respiratory chemoreceptors work by sensing the pH of their environment through the concentration of hydrogen ions. Because most carbon dioxide is converted to carbonic acid (and bicarbonate ) in the bloodstream, chemoreceptors are able to use blood pH as a way to measure the carbon dioxide levels of the bloodstream.
The main chemoreceptors involved in respiratory feedback are central chemoreceptors and Peripheral chemoreceptors:
Central chemoreceptors:
- These are located on the ventrolateral surface of medulla oblongata and detect changes in the pH of spinal fluid. They can be desensitized over time from chronic hypoxia (oxygen deficiency) and increased carbon dioxide.
- These include the aortic body, which detects changes in blood oxygen and carbon dioxide, but not pH, and the carotid body which detects all three. They do not desensitize, and have less of an impact on the respiratory rate compared to the central chemoreceptors.
D.6.U6 The rate of ventilation is controlled by the respiratory control center in the medulla oblongata
D.6.U7 During exercise the rate of ventilation changes in response to the amount of CO2 in the blood
During exercise the rate of ventilation changes in response to the amount of CO2 in the blood. Increased CO2 leads to a drop in blood pH. Chemoreceptors in the walls of the carotid arteries and the aorta, as well as chemoreceptors in the medulla itself, detect this pH change and send impulses to the Respiratory Control Centre in the medulla. Nerve impulses are sent along the intercostal and phrenic nerves causing them to increase ventilation rate.
If blood pH falls below 7.35 then the chemoreceptors we mentioned above increase the rate of ventilation and carbon dioxide is removed form the body. This CO2 has been formed at the alveolus from HCO-3 ions being added to H+ ions to form water and CO2. This has the effect of withdrawing the H+ ions from the blood. As pH is a measure of the amount of H+ ions then less of these ions means that the pH rises and the blood gets less acidic.
The kidney also plays a role in maintenance of blood pH. The kidney can secrete H+ ions into the urine in order to raise pH (less acidic). Greater amounts of hydrogen carbonate ions can be absorbed from the filtrate in the kidney which allows more CO2 formation at the lungs as outlined earlier ( ultimately less H+) and the resultant increase in pH.
During exercise the rate of ventilation changes in response to the amount of CO2 in the blood. Increased CO2 leads to a drop in blood pH. Chemoreceptors in the walls of the carotid arteries and the aorta, as well as chemoreceptors in the medulla itself, detect this pH change and send impulses to the Respiratory Control Centre in the medulla. Nerve impulses are sent along the intercostal and phrenic nerves causing them to increase ventilation rate.
If blood pH falls below 7.35 then the chemoreceptors we mentioned above increase the rate of ventilation and carbon dioxide is removed form the body. This CO2 has been formed at the alveolus from HCO-3 ions being added to H+ ions to form water and CO2. This has the effect of withdrawing the H+ ions from the blood. As pH is a measure of the amount of H+ ions then less of these ions means that the pH rises and the blood gets less acidic.
The kidney also plays a role in maintenance of blood pH. The kidney can secrete H+ ions into the urine in order to raise pH (less acidic). Greater amounts of hydrogen carbonate ions can be absorbed from the filtrate in the kidney which allows more CO2 formation at the lungs as outlined earlier ( ultimately less H+) and the resultant increase in pH.
D.6 U 8 Fetal hemoglobin is different from adult hemoglobin allowing the transfer of oxygen in the placenta into the fetal hemoglobin.
Fetal hemoglobin (HbF) is the main oxygen transport protein in the human fetus during the last seven months of development in the uterus and persists in the newborn until roughly 6 months old. Functionally, fetal hemoglobin differs most from adult hemoglobin in that it is able to bind oxygen with greater affinity than the adult form, giving the developing fetus better access to oxygen from the mother's bloodstream.
Fetal hemoglobin (HbF) is the main oxygen transport protein in the human fetus during the last seven months of development in the uterus and persists in the newborn until roughly 6 months old. Functionally, fetal hemoglobin differs most from adult hemoglobin in that it is able to bind oxygen with greater affinity than the adult form, giving the developing fetus better access to oxygen from the mother's bloodstream.
D.6.A1 Consequences of high altitude on gas exchange
At high altitudes, air pressure is lower and hence there is a lower partial pressure of oxygen (less O2 because less air overall)
At high altitudes, air pressure is lower and hence there is a lower partial pressure of oxygen (less O2 because less air overall)
- This makes it more difficult for haemoglobin to take up and transport oxygen (lower Hb % saturation)
- Consequently, respiring tissue will receive less oxygen – leading to symptoms such as fatigue, headaches and rapid pulse
- Red blood cell production will increase in order to maximise oxygen uptake and transport
- Red blood cells will have a higher haemoglobin count with a higher affinity for oxygen
- Vital capacity will increase to improve rate of gas exchange
- Muscles will produce more myoglobin and have increased vascularisation to improve overall oxygen supply
- Kidneys will begin to secrete alkaline urine (removal of excess bicarbonates improves buffering of blood pH)
- People living permanently at high altitudes will have a greater lung surface area and larger chest sizes
- Athletes may commonly either train at high altitudes (live low – train high) or recover at high altitudes (live high – train low)
D.6.A2 pH of Blood is regulated to stay within the narrow range of 7.35 to 7.45
D.6 A 3 Causes and treatments of emphysema.
Emphysema is a lung condition whereby the walls of the alveoli lose their elasticity due to damage to the alveolar walls
Causes of emphysema
Emphysema is a lung condition whereby the walls of the alveoli lose their elasticity due to damage to the alveolar walls
- The loss of elasticity results in the abnormal enlargement of the alveoli, leading to a lower total surface area for gas exchange
- The degradation of the alveolar walls can cause holes to develop and alveoli to merge into huge air spaces (pulmonary bullae)
Causes of emphysema
Consequences of emphysema
D.6 S 1 Analysis of dissociation curves for hemoglobin and myoglobin.
Myoglobin is an oxygen binding protein found in almost all mammals. It serves as a store of oxygen in muscles and it only releases it's attached oxygen when hemoglobin has already depleted its supplies. The partial pressure of oxygen in the tissues must be very low before myoglobin will dissociate its oxygen. This allows aerobic respiration to continue at very low partial pressure of oxygen in actively respiring tissues e.g. cardiac muscle.
All mammals have myoglobin in their muscle cells but some have more than others. Diving mammals e.g seals will have high levels of myoglobin stored in their muscle cells.
Myoglobin is an oxygen binding protein found in almost all mammals. It serves as a store of oxygen in muscles and it only releases it's attached oxygen when hemoglobin has already depleted its supplies. The partial pressure of oxygen in the tissues must be very low before myoglobin will dissociate its oxygen. This allows aerobic respiration to continue at very low partial pressure of oxygen in actively respiring tissues e.g. cardiac muscle.
All mammals have myoglobin in their muscle cells but some have more than others. Diving mammals e.g seals will have high levels of myoglobin stored in their muscle cells.
- Myoglobin has only one hem and carries only one O2 molecule
- Myoglobin has a greater affinity of O2 at lower partial pressure for oxtyem than hemoglobin
- The greater affinity means it acts as an O2 reservoir which is only released during intense physical activity (i.e high metabolic rate of respiring tissue)
D.6 S 2 Identification of pneumocytes, capillary endothelium cells and blood cells in light micrographs and electron micrographs of lung tissue.