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D6: Respiration - Coggle Diagram
D6: Respiration
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Smoking and emphysema
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Emphysema is the condition where the walls of the alveoli break down, so air sacs are fewer and larger.
The breaking down of alveolar walls reduces the surface area available for gaseous exchange causing fatigue and breathlessness. The lack of oxygen in tissues, especially the heart, can be a cause of death.
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Treatment consists of the use of bronchodilators that cause dilation of bronchi, corticosteroids to reduce inflammation, oxygen supplementation, and antibiotics if there are signs of infection.
Gas exchange
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The hydrogencarbonate buffering system: The rate at which gaseous exchange occurs depends on the pH of blood.
Within blood plasma and tissue fluids, hydrogencarbonate, proteins and ions (such as phosphate) act as buffers to maintain the pH close to neutral (slightly alkaline). Carbon dioxide combines with water producing carbonic acid that lowers the pH.
The carbonic acid dissociates into hydrogencarbonate that is alkaline, so it increases the pH, plus a hydrogen ion that acidifies the medium, decreasing the pH. This is called the hydrogencarbonate buffering system
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Oxygen transport in the blood: Once the first heme binds to oxygen, there is a small change in the protein structure of haemoglobin, making the heme of another chain join oxygen more easily. Cooperative oxygen binding by haemoglobin causes conformational changes in an individual peptide that are propagated to the other peptides.
Oxygen dissociation curve ------ The oxygen dissociation curve in Figure 1 shows how the partial pressure of oxygen (pO2) in the tissues determines the percentage of haemoglobin that contains oxygen at pH 7.4 and 38°C
As the blood leaves the heart, the partial pressure of oxygen decreases and the haemoglobin molecule releases one oxygen molecule. This causes an allosteric change in the haemoglobin molecule that makes the further release of the other oxygen molecules easier. --------> This means that a smaller drop in partial pressure is required to liberate a molecule of oxygen. In this way, haemoglobin attaches the largest possible amount of oxygen in the lungs
Fetal haemoglobin binds O2 with a greater affinity, therefore extracting it from the mother’s blood in the placenta. This means that at lower partial pressures of O2, the fetal haemoglobin loads O2 easier than adult haemoglobin. This would cause a shift to the left in the oxygen dissociation curve.
If you look at the graph from right to left, blood cells in the capillaries surrounding the alveoli carry 100% of the haemoglobin as oxyhaemoglobin. These capillaries lead to the pulmonary vein, which carries blood to the heart.
Myoglobin has a stronger affinity for oxygen than haemoglobin. Because myoglobin is formed by only one peptide, there is no allosteric effect in the molecule.
Bohr shift: An increase in blood acidity causes a shift of the oxygen dissociation curve to the right, and a decrease in acidity (a more alkaline pH) will cause a shift to the left.
The Bohr shift explains the increased release of oxygen by haemoglobin in respiring tissues.
As explained before, inside erythrocytes CO2 reacts with H2O forming H2CO3. The H2CO3 breaks down to H+ and HCO3-.