- The structural anatomy of the respiratory system is intimately linked to the physiologic requirements of breathing and gas exchange.
- The respiratory controller has both automatic and voluntary elements. Consciousness is not required to keep the system in motion, but behavioral factors can modify the rate and depth of breathing.
- Feedback from a variety of receptors in the respiratory system helps modulate the control of breathing.
- The vertebral column and the ribs support the muscles of ventilation and protect the lungs and other intrathoracic organs.
- The action of the muscles of ventilation is important in the development of negative and positive pressure within the thorax. The accessory muscles normally serve other functions but are recruited to assist the ventilatory pump when the body needs to increase the rate and depth of breathing or when the ventilatory pump is impaired.
- The pleurae link the motion of the chest wall and the lungs.
- The peripheral and autonomic nervous systems help translate activity in the controller into motion of the ventilatory pump, provide a means for the controller to assess the status of the pump, and play a role in establishing the diameter of the airways.
- The airways provide a conduit for the bulk flow of gas from the pharynx to the alveoli and back out again. They also serve an important role in defending the body against infection.
- The size and distribution of the airways reflect the need to balance airway resistance and dead space.
- Gas flow in the respiratory bronchioles and alveolar ducts is determined by diffusion rather than bulk flow.
- The gas exchanger is designed to maximize the area for diffusion of gases and minimize the distance between the alveolar lumen and the hemoglobin within the erythrocyte.
- The pulmonary circulation is a low-resistance system that has the capacity to hold much more blood than it contains when the body is resting.
- Pores of Kohn and the structural interconnectedness of alveoli contribute to the stability of the gas-exchanging units.
- Hypoxic pulmonary vasoconstriction in the lungs is an important mechanism for dbale matching blood flow and ventilation.
- Type II pneumocytes in the alveoli produce surfactant, a substance that plays an important role in reducing surface tension and preventing alveolar collapse.