Suffix

Combining Forms

Upper Respiratory Tract

The upper respiratory system encompasses the area from the nose to the larynx (Fig. 11-2). Air can enter the body through the mouth, but for the most part, it enters the body through the two nares (NAIR eez) (nostrils) of the nose that are separated by a partition called the nasal septum (NAY zul SEP tum). The hairs in the nose serve to filter out large particulate matter, and the mucous membrane and cilia (SEE lee uh) (small hairs) of the respiratory tract provide a further means of keeping air clean, warm, and moist as it travels to the lungs. The cilia continually move in a wavelike motion to push mucus and debris out of the respiratory tract. The air then travels up and backward, where it is filtered, warmed, and humidified by the environment in the upper portion of the nasal cavity. Fig. 11-3 illustrates the route of air into the body. The receptors for olfaction are located in the nasal cavity. The nasal cavity is connected to the paranasal sinuses (pair uh NAY zul SYE nus suhs), named for their proximity to the nose.

These sinuses, divided into the frontal, maxillary, sphenoid, and ethmoid cavities, acquire their names from the bones in which they are located. The function of sinus cavities in the skull is to warm and filter the air taken in and to assist in the production of sound. They are lined with a mucous membrane that drains into the nasal cavity and can be the site of painful inflammation.

Air continues to travel past into the nasopharynx (NAY zoh fair inks), which is the part of the throat (pharynx) behind the nasal cavity. The eustachian (yoo STAY shun) tubes from the ears connect with the throat at this point to equalize pressure between the ears and the throat. This is the site of lymphatic tissue, the pharyngeal tonsils (fur IN jee ul TAHN suls), which are also termed the adenoids (AD uh noyds). These pharyngeal tonsils help to protect against pathogens. The next structure, the oropharynx (or oh FAIR inks), is the part of the throat posterior to the oral cavity and also the location of more lymphatic tissue, the palatine tonsils (PAL ah tyne TAHN suls), so named because they are continuous with the roof of the mouth (the palate). These tonsils, just like the adenoids, are made up of protective lymphatic tissue. The lingual tonsil, located on the posterior aspect of the tongue, also serves a protective function. The oropharynx is also part of the digestive system; food and air pass through it. Below the oropharynx is the part of the throat referred to as the laryngopharynx (luh ring goh FAIR inks) because of its proximity to the adjoining structure, the larynx (LAIR inks), or voice box. As air passes back out through the opening of the larynx, the vocal cords, which are paired bands of cartilaginous tissue, vibrate to produce speech. The epiglottis (eh pee GLOT is) is a flap of cartilage at the opening to the larynx that closes access to the trachea (TRAY kee uh) during swallowing so that food is routed into the esophagus and is kept from entering the trachea. Though this is an effective protection most of the time, it can be overridden accidentally if the individual tries to talk and eat at the same time. When this happens, food can be pulled into the trachea, with possible serious consequences.

Lower Respiratory Tract

The lower respiratory tract begins with the trachea (or windpipe), which extends from the larynx into the chest cavity. The trachea lies within the space between the lungs called the mediastinum (mee dee uh STY num). Air travels into the lungs as the trachea bifurcates (branches) at the carina (kuh RIH nuh), where the right and left airways called bronchi (BRONG kee) (sing. bronchus) divide into smaller branches called bronchioles (BRONG kee ohls). These bronchioles end in microscopic ducts capped by air sacs called alveoli (al VEE oh lye) (sing. alveolus). Each alveolus is in contact with a blood capillary to provide a means of exchange of gases. It is at this point that O₂ is diffused across cell membranes into the blood cells, and CO₂ is diffused out to be expired. Each alveolus is coated with a substance called surfactant (sur FACK tunt) that keeps it from collapsing.

Each lung is composed of sections called lobes. The right lung is made up of three sections, whereas the left has only two. The abbreviations for the lobes of the lungs are RUL (right upper lobe), RML (right middle lobe), RLL (right lower lobe), LUL (left upper lobe), and LLL (left lower lobe).

Each lung is also enclosed by a double-folded, serous membrane called the pleura (PLOOR uh) (pl. pleurae). The side of the membrane that coats the lungs is the visceral pleura (VIH sur ul PLOOR ah); the side that lines the inner surface of the rib cage is the parietal pleura (puh RYE uh tul PLOOR ah). The two sides of the pleural membrane contain fluid that facilitates the expansion and contraction of the lungs with each breath.

The muscles responsible for normal, quiet respiration are the diaphragm (DYE uh fram), the large dome-shaped muscle between the thoracic and abdominal cavities, and the intercostal (in tur KOS tul) muscles, which are located between the ribs. On inspiration, the diaphragm is pulled down as it contracts and the intercostal muscles expand, pulling air into the lungs (see Fig. 11-1, B).