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Resp 2 Checklist Lower Respiratory Tract Lower respiratory tract The lower respiratory tract consists of the larynx, tracheobronchial tree, and lungs. Larynx, or voice box The larynx, or voice box, is the beginning of the lower respiratory tract. It consists of cartilage, laryngeal skeletal muscles, and the vocal cords. Most of the larynx is inferior to the hyoid bone, but a small part of the larynx is superior to the hyoid bone. The larynx is superior to, and connects with, the trachea. Functions of the larynx 1. Laryngeal cartilages form a passageway for air flow. During inspiration, air passes through the nasal cavity or oral cavity, enters the oropharynx, goes into the larynx, and flows on through to the lungs. During expiration, air flows in the reverse direction. 2. Air passing through the larynx vibrates the vocal cords in the larynx, resulting in sound production. 3. During swallowing, laryngeal muscles and cartilage close the opening into the larynx, preventing swallowed materials from entering the larynx. Laryngopharynx The laryngopharynx is posterior to the larynx. It extends to the inferior border of the larynx and cervical vertebra C6. The laryngopharynx connects to the superior opening of the larynx. Air from the nasal or oral cavities can pass through the laryngopharynx and enter the larynx. The laryngopharynx connects to the esophagus, a tube which conducts swallowed food and liquids to the stomach. Laryngeal cartilages Nine pieces of cartilage form the larynx. There are three unpaired cartilages: the thyroid cartilage, cricoid cartilage, and the epiglottis. There are three paired cartilages: arytenoid, corniculate, and cuneiform. Thyroid cartilage The thyroid cartilage is the largest and most prominent laryngeal cartilage. It forms a protrusion of the throat called the "Adams apple." At puberty, the larynx of males becomes larger than the larynx of females. The thyroid cartilage, in particular, increases in size and projects anteriorly. 1 During swallowing, muscles attached to the thyroid cartilage and other parts of the larynx pull the larynx superiorly and anteriorly. This allows the pharynx to expand and moves the laryngeal opening out of the way of swallowed materials. Cricoid cartilage The cricoid cartilage (pink) forms the base of the larynx, connecting it to the trachea. Epiglottis The third unpaired laryngeal cartilage is the epiglottis. During swallowing, the larynx moves superiorly and anteriorly. Upward movement of the epiglottis is prevented, however, by the base of the tongue. As a result, the epiglottis folds over the opening of the larynx. In addition, as solid swallowed materials slide over the epiglottis, they push on it, helping to fold it over the laryngeal opening. Analogy: The epiglottis is like the lid on a toilet seat. When the lid is down, nothing goes into the toilet (larynx). In humans, the epiglottis is not essential for swallowing. The laryngeal muscles (considered later in this lesson) prevent materials from entering the larynx. Even if the epiglottis is destroyed by disease, swallowing can still occur without materials entering the larynx. Cricothyrotomy A cricothyrotomy is an emergency procedure used when the larynx becomes obstructed and a person is suffocating. The thyroid cartilage can be easily felt with a finger on the midline of the anterior neck. Moving the finger inferiorly, an indentation can be felt. This is the location of the cricothyroid membrane between the thyroid and cricoid cartilages. In a cricothyrotomy, a small slit is made through the cricothyroid membrane and a tube is inserted into the inferior larynx and into the trachea, permitting air flow to occur. Arytenoid cartilages The paired arytenoid cartilages rest on the cricoid cartilage. Corniculate cartilages The paired corniculate cartilages rest on the arytenoid cartilages. Cuneiform cartilages The paired cuneiform cartilages are small cartilages located in mucous membranes. Vestibular folds The vestibular folds are mucous membranes covering the vestibular ligaments, which are stretched between the thyroid cartilage and the arytenoid cartilages. The vestibular folds are sometimes called the false vocal cords. 2 The vestibular folds can open and close. During respiration they open, allowing the movement of air. During swallowing, they close to prevent the movement of swallowed materials into the larynx. If the epiglottis is represented by the toilet seat cover, then the vestibular folds are the toilet seat. Unlike a toilet seat, however, the vestibular folds can change shape. Muscles associated with the arytenoid cartilages cause them to move. As a result, the attached vestibular folds change shape and meet at the midline, thus closing the passageway into the larynx. Vocal folds The vocal folds are mucous membranes covering the vocal ligaments, which are stretched between the thyroid cartilage and the arytenoid cartilages. The vocal folds are sometimes called the true vocal cords. The movement of air past the vocal folds causes them to vibrate, producing sounds, such as speech. The greater the movement of air, the greater the vibration, and the louder the sound. The pitch of the sound can be changed by altering the length of the vocal folds. As the length of the vocal folds increases, they stretch and are under greater tension, resulting in a higher pitch sound. Muscles associated with the arytenoid cartilages cause them to move. When the muscles contract, the tension of the attached vocal folds increases, and when the muscles relax, the tension decreases. Ventricle of the larynx The ventricle of the larynx is the space between the vestibular and vocal folds. The ventricle of the larynx opens into a sac (laryngeal saccule) containing numerous mucous glands. Compression of the sac by surrounding muscles causes the secretions of these glands to be pushed onto the vocal folds. The secretions help to keep the vocal folds from drying out. The vocal folds are covered with moist stratified squamous epithelium and do not have mucous glands. In some monkeys, the sacs are enlarged to form air sacs that cause sounds to resonate and increase in volume. Howler monkeys have been know to project their sounds up to a distance of 5 miles. 3 Trachea, or wind pipe The trachea is a tube consisting of 15-20 C-shaped pieces of cartilage connected by a fibrous membrane and smooth muscle. The trachea is approximately 11 cm (4.3 in) long, extending from the larynx to the level of the fifth thoracic vertebra, where it divides. Functions of the trachea 1. The tracheal cartilages keep the trachea from collapsing, thus maintaining an open passageway for the movement of air to and from the lungs. 2. Smooth muscles within the tracheal wall can regulate the diameter of the trachea. For example, during exercise the muscles relax, diameter increases, and a greater volume of air movement results. 3. The trachea is lined with pseudostratified columnar ciliate epithelium that traps and removes inhaled debris in the air. Thyroid gland An endocrine gland with two lobes located immediately lateral to each side of the trachea. Typically, the two lobes are connected across the anterior surface of the trachea by a piece of thyroid tissue called the isthmus. The thyroid gland produces thyroid hormones, which increase metabolic rate and are essential for normal growth and maturation. If it is necessary to make a permanent opening into the trachea, a tracheostomy is performed. In this procedure, an incision is made through the skin and the muscles overlying the trachea are retracted. If the isthmus cannot be pushed out of the way, it is tied off and cut along the midline to expose the trachea. Typically, the anterior part of the second tracheal ring is removed to provide a "window" into the trachea. A tracheostomy is not an emergency procedure and should be performed only by individuals trained in the procedure so as not to damage the thyroid gland. A tracheostomy is not performed inferior to the third tracheal cartilage because the trachea become too deep for easy access. Primary bronchi The trachea branches to form two smaller tubes called primary bronchi. The primary bronchi also branch to form even smaller tubes. These subdivisions continue to divide and become even smaller until they end as microscopically small sacs. 4 Tracheobronchial tree The trachea and all of these branches are called the tracheobronchial tree. The tracheobronchial tree forms the passageways through which air moves to and from the sites where gases are exchanged between the air and the blood. The tracheal cartilages are C-shaped pieces of cartilage. From the anterior view, they form solid bands of cartilage connected by a fibrous membrane. The cartilages hold the trachea open so that air can flow uninterrupted. Trachealis muscles The trachealis muscles are smooth muscles that connect the ends of the tracheal cartilages. Contraction and relaxation of the trachealis muscles can change the diameter of the trachea by pulling the ends of the cartilages closer together. For example, during coughing, the trachealis muscles contract, which decreases the diameter of the trachea. As a result, air flows through the trachea more rapidly, causing mucus or foreign objects to be expelled. Esophagus The esophagus is located between the trachealis muscles and the vertebral column. The esophagus, which conducts swallowed materials to the stomach, is normally flattened. When food is swallowed, the esophagus can momentarily expand into the trachea because the posterior part of the trachea does not have cartilage. Primary bronchi The trachea branches to form the left and right primary bronchi, which go to the left and right lungs. Lung One of two cone-shaped organs located in the thoracic cavity. The base of the lung rests upon the diaphragm, and its apex extends 2.5 cm (1 in) superior to the clavicle. The adult right lung weighs about 625 gm (1.4 lb) and the left lung 565 gm (1.2 lb). The lungs are the organs of respiration. During inspiration, air moves into the lungs. Oxygen in the air moves into the blood, and carbon dioxide, produced by the body, moves from the blood into the air. During expiration, air moves out of the lungs. Mediastinum The mediastinum is the partition separating the two lungs. It contains all of the thoracic organs, except for the lungs. The major organs of the mediastinum include the heart, blood vessels going to and from the heart, the trachea, and the esophagus. 5 Great vessels The great vessels carry blood to and from the heart. The superior vena cava returns deoxygenated blood from the head, thorax, and upper limbs to the heart. The aorta delivers oxygenated blood to the body. The pulmonary trunk delivers deoxygenated blood to the lungs. The pulmonary trunk divides to form the left and right pulmonary arteries, which go to the left and right lungs. After the blood is oxygenated in the lungs, it returns to the heart through the four pulmonary veins. Hilum The hilum is part of the lung where the primary bronchus and pulmonary artery enter the lung and the pulmonary veins exit the lung. Lung impressions The lungs conform to the shape of the organs with which they come into contact. The cardiac impression is the indentation of the lung where it partially surrounds the left side of the heart. The groove for the aorta is the medial indentation of the left lung where it partially surrounds the aorta. The diaphragmatic surface is the inferior indentation of the lung where it partially surrounds the diaphragm. The indentations for the superior vena cava and other blood vessels are in the right lung. The groove for the trachea and esophagus are in the right lung. Secondary bronchi The primary bronchi branch to form the secondary bronchi. The secondary bronchi supply subdivisions of the lungs called lobes. In the left lung, there are two secondary bronchi, which supply the superior and inferior lobes. In the right lung, there are three secondary bronchi, which supply the superior, middle, and inferior lobes. Tertiary bronchi The secondary bronchi branch to form the tertiary bronchi. The tertiary bronchi supply subdivisions of the lobes called bronchopulmonary segments. 6 In the left lung, there are nine bronchopulmonary segments. In the right lung, there are ten bronchopulmonary segments. The bronchopulmonary segments are separated from one another by connective tissue partitions. Diseased bronchopulmonary segments can be removed from the lungs because major bronchi and blood vessels do not cross the partitions. Alveoli The tertiary bronchi divide into smaller branches, which also divide, and so on, until many small tubes are produced. The small tubes are associated with air sacs called alveoli, which are the site of gas exchange between the air and blood. Mediastinum The mediastinum is the partition separating the two lungs. The major organs of the mediastinum are the heart, esophagus, aorta, and azygos vein. Pleural cavity Each lung is surrounded by a space called the pleural cavity. Pleural membrane The pleural membrane forms the boundary of the pleural cavity. The pleural membrane is divided into two parts. The visceral pleura covers the surface of the lungs. The parietal pleura lines the inner surface of the thoracic wall, the diaphragm, and the mediastinum. Pleural membrane functions The visceral and parietal pleurae secrete pleural fluid, which fills the pleural cavity. Pleural fluid is a lubricant that allows the visceral pleura to slide past the parietal pleura as the lungs and thorax change shape during respiration. Pleural fluid holds the visceral and parietal pleurae together. For example, as the thorax expands during inspiration, the lungs also expand because they are connected through the pleurae to the thoracic wall. 7 Application Question 9. If the air passageways should become obstructed, an endoscope can be used to insert a tube through the mouth into the trachea. Given the following list of structures, arrange them in the order the tube would pass through or by them. Epiglottis Laryngopharynx Oral cavity Oropharynx Vestibular folds Vocal folds 8 Application Answer 9. A tube passing through the mouth to the trachea passes through or by the following: Oral cavity Oropharynx Laryngopharynx Epiglottis Vestibular folds Vocal folds 9