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Review of Lungs, Oxygen and CO2 transport
Review of Lungs, Oxygen and CO2 transport
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Basic Summary of Information
Basic Summary of Information
Oxygen dissociation curves show the affinity of haemoglobin for oxygen
Oxygen dissociation curves show the affinity of haemoglobin for oxygen
Carbon dioxide is carried in solution and bound to haemoglobin in the blood
Carbon dioxide is carried in solution and bound to haemoglobin in the blood
Carbon dioxide is transformed in red blood cells into hydrogen carbonate ions
Carbon dioxide is transformed in red blood cells into hydrogen carbonate ions
The Bohr shift explains the increased release of oxygen by haemoglobin in respiring tissues
The Bohr shift explains the increased release of oxygen by haemoglobin in respiring tissues
Chemoreceptors are sensitive to changes in blood pH
Chemoreceptors are sensitive to changes in blood pH
The rate of ventilation is controlled by the respiratory control centre in the medulla oblongata
The rate of ventilation is controlled by the respiratory control centre in the medulla oblongata
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
Fetal haemoglobin is different from adult haemoglobin allowing the transfer of oxygen in the placenta onto the fatal haemoglobin
Fetal haemoglobin is different from adult haemoglobin allowing the transfer of oxygen in the placenta onto the fatal haemoglobin
Oxygen is transported throughout the body in red blood cells, which contain an oxygen-binding protein called haemoglobin
Oxygen is transported throughout the body in red blood cells, which contain an oxygen-binding protein called haemoglobin
- Haemoglobin is composed of four polypeptide chains, each with an iron-containing heme group that reversibly binds oxygen
- As such, each haemoglobin can reversibly bind up to four oxygen molecules (Hb + 4O2 = HbO8)
As each O2 molecule binds, it alters the conformation of haemoglobin, making subsequent binding easier (cooperative binding)
As each O2 molecule binds, it alters the conformation of haemoglobin, making subsequent binding easier (cooperative binding)
- This means haemoglobin will have a higher affinity for O2 in oxygen-rich areas (like the lung), promoting oxygen loading
- Conversely, haemoglobin will have a lower affinity for O2 in oxygen-starved areas (like muscles), promoting oxygen unloading
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The greater the tendency to bind with oxygen, the higher the affinity.
The greater the tendency to bind with oxygen, the higher the affinity.
Haemoglobin molecules that are already carrying three oxygen molecules have the greatest affinity for oxygen. Conversely, haemoglobin molecules that are carrying no oxygen molecules have the least affinity for oxygen. You might think that this does not make sense, but it does when you learn that each oxygen molecule that binds to haemoglobin changes the haemoglobin’s shape in a way that increases its affinity for another oxygen molecule. Haemoglobin can carry a maximum of four oxygen molecules, so one that is already carrying four oxygens has no affinity for oxygen.
Oxygen Dissociation Curves
Oxygen Dissociation Curves
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
Adult Haemoglobin
Adult Haemoglobin
- 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)
Fetal Haemoglobin
Fetal Haemoglobin
- The haemoglobin of the foetus has a slightly different molecular composition to adult haemoglobin
- Consequently, it has a higher affinity for oxygen (dissociation curve is shifted to the left)
- This is important as it means fetal haemoglobin will load oxygen when adult haemoglobin is unloading it (i.e. in the placenta)
- Following birth, fetal haemoglobin is almost completely replaced by adult haemoglobin (~ 6 months post-natally)
- Fetal haemoglobin production can be pharmacologically induced in adults to treat diseases such as sickle cell anaemia
Myoglobin
Myoglobin
- Myoglobin is an oxygen-binding molecule that is found in skeletal muscle tissue
- It is made of a single polypeptide with only one heme group and hence is not capable of cooperative binding
- Consequently, the oxygen dissociation curve for myoglobin is not sigmoidal (it is logarithmic)
- Myoglobin has a higher affinity for oxygen than adult haemoglobin and becomes saturated at lower oxygen levels
- Myoglobin will hold onto its oxygen supply until levels in the muscles are very low (e.g. during intense physical activity)
- The delayed release of oxygen helps to slow the onset of anaerobic respiration and lactic acid formation during exercise
The Bohr shift explains the increased release of oxygen by haemoglobin in respiring tissues
The Bohr shift explains the increased release of oxygen by haemoglobin in respiring tissues
You should be able to draw and explain this graph
You should be able to draw and explain this graph
The oxyhaemoglobin dissociation curve demonstrates the saturation of haemoglobin by oxygen under normal conditions
- pH changes alter the affinity of haemoglobin for oxygen and hence alters the uptake and release of O2 by haemoglobin
Carbon dioxide lowers the pH of the blood (by forming carbonic acid), which causes haemoglobin to release its oxygen
- This is known as the Bohr effect – a decrease in pH shifts the oxygen dissociation curve to the right
Cells with increased metabolism (i.e. respiring tissues) release greater amounts of carbon dioxide (product of cell respiration)
- Hence haemoglobin is promoted to release its oxygen at the regions of greatest need (oxygen is an input of cell respiration)
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