Summary
Highlights
Pulmonary arteries deliver deoxygenated blood to the lungs for oxygenation, branching with the bronchioles to capillary beds around the alveoli. Oxygenated blood returns to the heart via pulmonary veins. The lungs are encased by the pleura, a serous membrane with two layers: visceral (covering the lungs) and parietal (lining the thoracic cavity). The pleural cavity between them contains lubricating fluid to reduce friction during breathing.
The respiratory system is responsible for breathing, which includes external respiration (inhalation and exhalation) and internal respiration (gas exchange between blood and tissues). It brings oxygen into the body and expels carbon dioxide, regulates pH, protects against pathogens, and aids in vocalization.
The respiratory system is divided into upper and lower tracts. The upper tract includes the nose, nasal cavity, mouth, pharynx, and larynx. The nose and nasal cavities filter, warm, and humidify the air. The pharynx connects the mouth and nasal cavity to the larynx and esophagus, divided into nasopharynx, oropharynx, and laryngopharynx. The larynx is crucial for phonation, containing vocal cords and cartilage to prevent food from entering the airway.
The larynx is supported by nine cartilages: three unpaired (thyroid, cricoid, and epiglottis) and three paired (arytenoid, corniculate, and cuneiform). The thyroid cartilage forms the 'Adam's apple.' The cricoid cartilage is ring-shaped. The epiglottis prevents food from entering the trachea during swallowing. The paired cartilages contribute to vocal cord movement and airway closure.
The lower respiratory tract consists of the trachea, bronchi, bronchioles, and lungs. The trachea is a cylindrical tube supported by C-shaped cartilaginous rings, extending from the larynx to the bronchi. It branches into two main bronchi, one for each lung. The right bronchus is wider, shorter, and more vertical, making it more prone to foreign object aspiration.
Inside the lungs, the main bronchi divide repeatedly into smaller bronchi, then into bronchioles, forming the 'bronchial tree.' The epithelium lining changes along this path. The smallest bronchioles lead to respiratory bronchioles, alveolar ducts, alveolar sacs, and finally alveoli. Alveoli are tiny air sacs where gas exchange (hematosis) occurs between air and blood capillaries.
The lungs are essential organs for respiration, light, soft, and elastic. They change color over time due to inhaled particles. The right lung is larger and heavier than the left, which accommodates the heart. Each lung has a superior and inferior lobe, while the right lung additionally has a middle lobe. They have a curved apex, a concave base, and distinct costal and mediastinal surfaces. The hilum is the entry/exit point for blood vessels, bronchi, nerves, and lymphatic vessels.