Anatomy of the Respiratory System

The Nose
The nose is the only externally visible part of the respiratory system that allows breathing as air passes through the nostrils or external nares. The nasal cavity is divided by a midline nasal septum. Olfactory receptors are found in the mucosa. The nose provides the sense of smell. Mucosa are found in the slit-like superior of the nasal cavity and also found lining the nasal cavity; called the respiratory mucosa. The respiratory mucosa rest on thin-walled veins that warm the air as it flows past. Mucosa produce sticky mucus which moistens air, traps bacteria, and catches debris. The lateral walls are uneven due to 3 projections called conchae. The concha increases surface area of the mucosa exposed to air and also increases turbulence, increasing the chance of catching debris. The nose is separated from the oral cavity via palates. The bone supported palate is the hard palate, while the unsupported is the soft palate. The nasal cavity is surrounded by paranasal sinuses.

Pharynx
The pharynx is a muscular passageway, commonly known as the throat. It serves as a passageway for food and air. The pharynx is continuous with the nasal cavity anteriorly via the internal nares. The superior portion is called the nasopharynx. The Oropharynx and laryngopharynx are the inferior portion. The pharynx connects to the larynx.

Larynx
The larynx routes air and food into the proper channels. It plays a role in speech. The larynx is formed by 8 rigid hyaline cartilages and the epiglottis. The largest of the hyaline cartilages is called the thyroid cartilage. It protrudes, and is commonly called the adam’s apple. The epiglottis protects the superior opening of the larynx. It forms a lid over the larynx when eating. If food enters the larynx, cough reflexes occur. Some mucous membrane in the larynx form vocal folds. It vibrates with expelled air. It allows the ability to speak. The slit-like passageway between the vocal folds is the glottis.

Trachea
Also known as the “windpipe,” the trachea allows the esophagus to expand when swallowing large foods. Air travels down to the fifth thoracic vertebra (midchest). Walls of the trachea are reinforced with hyaline cartilage, which keeps walls open during pressure changes in breathing.

Main Bronchi
The main bronchi consists of the right and left bronchi. The right bronchus is wider, shorter, and straighter than the left. It runs obliquely before connecting to the lung. Smaller divisions of the main bronchi within the lungs are routes to the air sacs.

Lungs
The lungs are paired organs that occupy the entire thoracic cavity except the central mediastinum. Narrow superior portions of each lung are called the apex. The broad lung area resting on the diaphragm is the base. The surface of each lung is covered with visceral serosa called the pulmonary or visceral pleura. The walls of the thoracic cavity are lined by the parietal pleura. Pleural membranes produce pleural fluid, which provide lubrication during breathing and causes the pleural layers to cling together. Pleurae can slide across each other easily but resist being pulled apart. It allows lungs to be held tightly to the thorax wall and creates pleural space.