The airways are also prone to being affected by hypersensitivity reactions – these are abnormal immune responses to normal stimuli. These are categorised into 4 different types. Type 1 This is a rapid allergic reaction due to pre-formed IgE antibody to an exposed antigen. – It eventually leads to a large increase in histamine which can lead to anaphylactic shock. Histamine is stored in mast cells and is released by calcium-dependent exocytosis: – IgE binds IgE receptor –> increases intracellular IP3 –> increases Calcium – Intracellular cAMP is an antagonist and works to block release of histamine Histamine
At the lungs, alveolar ventilation is matched with pulmonary blood flow to create a concentration gradient to exchange O2 and CO2 – Oxygen binds to haemoglobin and is transported in the blood. – The dissociation curve is sigmoidal, due to the cooperative binding of oxygen molecules. – This means that it is at first difficult to load the first oxygen molecule onto haemoglobin – However, once the first one binds, this causes a conformational shift which increases haemoglobin’s affinity for oxygen It is then easier to bind the next oxygen molecules. This causes the steep rise in the oxygen dissociation
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