The thoracic cage, sometimes called the rib cage, is a bony structure that is narrower at the top and wider at the base. It is held in place by the thoracic vertebrae of the spine in the center of the back and by the sternum in the center of the anterior aspect of the body. The first seven ribs attach directly to the sternum and are called the true ribs. Ribs 8, 9, and 10 fasten one to another, forming the false ribs, and ribs 11 and 12 are the “floating” ribs, or half ribs, because their only attachment is to the thoracic vertebrae. At the base or floor of the rib cage is the diaphragm, a musculotendinous membrane that separates the thoracic cavity and the abdominal cavity (Figure 46-1). The respiratory system is divided into two anatomic regions, the upper respiratory tract and the lower respiratory tract.

Upper Respiratory Tract

The upper respiratory tract, which transports air from the atmosphere to the lungs, includes the nose, pharynx (throat), and larynx (Figure 46-2). As air enters the nasal cavity, it is cleaned by the cilia, warmed by capillary blood vessels, and moistened by mucous membranes. The paranasal sinuses, hollow cavities that also are lined with mucous cells and cilia, open into the nasal cavity and help warm and moisten inhaled air. The filtered, warmed, and moistened air moves past the tonsils, which have an immunity function and help defend the body from potential pathogens, and through the pharynx. As the air continues toward the lungs, it passes through the larynx. The opening into the larynx is protected by a moveable piece of cartilage, the epiglottis. The larynx, or voice box, is made up of vocal cords, which vibrate when air is exhaled, creating the sound of the voice. Once the air passes through the larynx, it enters the lower respiratory tract.

4 0

3 years ago