lungs
Summary
The lungs are paired respiratory organs responsible for gas exchange between air and blood. They contain millions of alveoli where oxygen diffuses into pulmonary capillaries and CO2 is removed. Essential for maintaining acid-base balance and oxygenation of tissues.
Detail
The lungs are bilateral spongy organs located in the thoracic cavity, divided into lobes (right lung: 3 lobes, left lung: 2 lobes). The respiratory system includes conducting airways (trachea, bronchi, bronchioles) and respiratory zones (respiratory bronchioles, alveolar ducts, alveoli). Gas exchange occurs across the respiratory membrane in ~300 million alveoli, where oxygen binds to hemoglobin and CO2 is eliminated. Ventilation is driven by diaphragmatic and intercostal muscle contraction. The lungs are perfused by both pulmonary circulation (deoxygenated blood from right ventricle) and bronchial circulation (oxygenated blood from systemic circulation). Surfactant produced by type II pneumocytes reduces surface tension, preventing alveolar collapse. The lungs also function in pH regulation through CO2 elimination and serve as filters for blood clots and air emboli.
Sources
- Guyton and Hall Textbook of Medical Physiology
- West's Respiratory Physiology
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
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