Key points The entire cardiac output passes through the pulmonary circulation, so the lungs act as a filter, preventing emboli from passing to the left side of the circulation. The lungs constitute a huge interface between the outside environment and…
Key points Oxygen moves down a partial pressure gradient between the inspired gas and its point of use in the mitochondria, where the oxygen partial pressure may be only 0.13 kPa (1 mmHg). Significant barriers to oxygen transfer are between…
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Key points For gas to transfer between the alveolus and haemoglobin in the red blood cell it must diffuse across the alveolar and capillary walls, through the plasma and across the red cell membrane. The reaction rate for oxygen with…
Key points Both ventilation and perfusion are distributed preferentially to dependent regions of the lung as a result of gravity and lung structure, and vary with posture and lung volume. In healthy lungs ventilation and perfusion are closely matched, with…
Key points Pulmonary blood flow approximates to cardiac output and can increase several-fold with little change in pulmonary arterial pressure. Passive distension and recruitment of closed pulmonary capillaries, particularly in the upper zones of the lung, allow pulmonary vascular resistance…
Key points Pharyngeal and laryngeal muscles display both tonic and phasic contraction to maintain airway patency and to regulate airflow. The diaphragm, the intercostal muscles and some neck muscles bring about inspiration by a complex combination of actions, varying with…
Key points The respiratory centre in the medulla generates the respiratory rhythm using an oscillating network of groups of interconnecting neurones. Many other diverse areas of the central nervous system influence respiratory control, and these connections are coordinated by the…
Key points Gas flow in the airway is a mixture of laminar and turbulent flow, becoming more laminar in smaller airways. Respiratory system resistance is a combination of resistance to gas flow in the airways and resistance to deformation of…
Key points Inward elastic recoil of the lung opposes outward elastic recoil of the chest wall, and the balance of these forces determines static lung volumes. Surface tension within the alveoli contributes significantly to lung recoil and is reduced by…