GLOSSARY OF TERMS |
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NASOPHARYNX: The nasopharynx is situated behind the nasal cavity, above the soft palate. It communicates with the nasal cavities through the nasal choanae and with the tympanic cavity through the eustachian tube. It contains the pharyngeal tonsils in its posterior wall. OROPHARYNX: The oropharynx is encompassed by the soft palate above and the epiglottis below. It communicates with the mouth through the oropharyngeal isthmus. It contains the palatine tonsils. PALATE: The palate forms the roof of the mouth and the floor of the nasal cavity. The hard palate forms the anterior four-fifths of the palate and is a bony framework covered with a mucus membrane. The soft palate, comprising the posterior one-fifth of the palate, is a fibromuscular fold that moves posteriorly against the pharyngeal wall to close the oropharyngeal cavity when swallowing or speaking. PHARYNX: The pharynx is a U-shaped fibromuscular structure located between the oral and nasal cavities and posterior to the larynx. It is subdivided into the NASOPHARYNX, OROPHARYNX, and LARYNGOPHARYNX/ HYPOPHARYNX. It extends from the base of the skull to the inferior border of the cricoid cartilage anteriorly (at the entrance of the esophagus) and the inferior border of the C6 vertebra posteriorly. The pharynx conducts food to the esophagus and air to the larynx, trachea and lungs. It opens anteriorly into the nasal cavity, mouth and larynx (naso-, oro-, and laryngo- pharynx, respectively) and to the esophagus posteriorly. The wall of the pharynx is composed of two layers of pharyngeal muscles: the external circular layer consists of constrictors and the internal longitudinal layer consists of muscles that elevate the larynx and pharynx during swallowing and speaking. EPIGLOTTIS: The epiglottis is a spoon shaped plate of elastic cartilage that lies behind the tongue. It prevents aspiration by covering the glottis – the opening of the larynx - during swallowing. LARYNGOPHARYNX/HYPOPHARYNX: The laryngopharynx/hypopharynx extends from the upper border of the epiglottis to the lower border of the cricoid cartilage. It contains the piriform recesses, at each side of the opening of the larynx, in which swallowed foreign materials may be lodged. LARYNX: The larynx is a cartilaginous skeleton held together by ligaments and muscles. The nine cartilages of the larynx are the thyroid, cricoid, epiglottic and (in pairs) the arytenoid, corniculate and cuneiform. The larynx serves as a sphincter to prevent the passage of food and drink into the trachea and lungs during swallowing, It also contains the vocal cords and regulates the flow of air to and from the lungs for phonation. It is through the abducted vocal cords of the larynx that an endotracheal tube is advanced during endotracheal intubation TRACHEA: The trachea begins at the inferior border of the cricoid cartilage (C6) and continues about 9-15 cm in length until it bifurcates into the right and left main bronchi at the level of the sternal angle (junction of T4 and T5). It is composed of 16-20 incomplete cartilaginous rings that open posteriorly to prevent the trachea from collapsing. These incomplete rings allow for changes in caliber which can be important in changing airway resistance and in generating a cough. RIGHT AND LEFT MAIN BRONCHUS: The right and left main bronchi pass inferolaterally from the bifurcation of the trachea to the lungs. They are supported by cartilaginous rings. The right main bronchus is wider, shorter, and more vertical than the left, and thus is the more common side of foreign body obstruction. Both main bronchi accompany the pulmonary arteries into the hila of the lungs and branch within the lung to form the bronchial tree. CARINA: The carina is a downward and backward projection of the last tracheal cartilage. It forms a ridge that separates the opening of the right and left main stem bronchi. It occurs at the sternal angle, the junction of T4 and T5. BRONCHOPULMONARY SEGMENT: The bronchopulmonary segment is the anatomical, functional, and surgical unit/subdivision of the lung and refers to the portion of the lung supplied by each segmental/tertiary bronchus and segmental/tertiary artery. It consists of the segmental/tertiary bronchus, a segmental branch of the tertiary artery, a segment of the lung tissue, and the surrounding connective-tissue septum. The bronchopulmonary segment is important because a surgeon can remove one segment without seriously disrupting surrounding segments. DIAPHRAGM:The Diaphragm is the most important muscle for inspiration. When the diaphragm contracts, the abdominal contents are pushed downward and the ribs are lifted upwards and outwards, increasing the volume and decreasing the pressure in the thoracic cavity. Remember the pneumonic: C3,C4, C5 keep the diaphragm alive! THORACIC CAGE: The muscles of the thoracic cage, the external intercostals and the accessory muscles, are used only during exercise/exertion, not during normal quiet breathing. In fact, use of intercostal muscles, as in retractions, often indicates increased work of breathing and impending respiratory failure. SURFACTANT: Surfactant is synthesized by type II alveolar cells/pneumocytes and consists primarily of DPPC, Dipalmitoyl phosphatidylcholine. COMPLIANCE:Compliance is the ability of the lung to stretch; its distensibility. It represents the change in volume that occurs for a given change in pressure. HEMOGLOBIN:Hemoglobin is composed of four globin subunits, each centered around a heme group (iron containing porphyrin rings) whose central iron atom binds reversibly with an oxygen molecule. The oxygen-hemoglobin bond is a weak one and can be disrupted without altering either the hemoglobin or oxygen. Because there are four iron atoms in each hemoglobin molecule, each hemoglobin molecule can bind up to four oxygen molecules. Hemoglobin bound to oxygen is known as oxyhemoglobin. The percent saturation of hemoglobin (or, simply, oxygen saturation) refers to the percent of available binding sites that are bound to oxygen. The oxygen saturation of arterial blood with a PO2 of 100 mmHg is about 97.5%, whereas that of mixed venous blood with a PO2 of 40 mm Hg is about 75% |