Review Sheet 23 Anatomy of the Respiratory System

Learning Objectives

By the end of this section, you will exist able to:

• Listing the structures that make upwards the respiratory organisation
• Depict how the respiratory system processes oxygen and CO₂
• Compare and contrast the functions of upper respiratory tract with the lower respiratory tract

The major organs of the respiratory system function primarily to provide oxygen to torso tissues for cellular respiration, remove the waste matter carbon dioxide, and help to maintain acid-base residual. Portions of the respiratory system are too used for non-vital functions, such as sensing odors, spoken language production, and for straining, such every bit during childbirth or coughing (Effigy 22.two).

Figure 22.2 Major Respiratory Structures The major respiratory structures span the nasal cavity to the diaphragm.

Functionally, the respiratory system can be divided into a conducting zone and a respiratory zone. The conducting zone of the respiratory arrangement includes the organs and structures non directly involved in gas substitution. The gas exchange occurs in the respiratory zone.

Conducting Zone

The major functions of the conducting zone are to provide a route for incoming and outgoing air, remove debris and pathogens from the incoming air, and warm and humidify the incoming air. Several structures inside the conducting zone perform other functions as well. The epithelium of the nasal passages, for example, is essential to sensing odors, and the bronchial epithelium that lines the lungs tin metabolize some airborne carcinogens.

The Olfactory organ and its Next Structures

The major entrance and exit for the respiratory system is through the nose. When discussing the nose, it is helpful to dissever it into two major sections: the external nose, and the nasal crenel or internal nose.

The external olfactory organ consists of the surface and skeletal structures that issue in the outward appearance of the nose and contribute to its numerous functions (Figure 22.three). The root is the region of the nose located between the eyebrows. The bridge is the part of the nose that connects the root to the rest of the olfactory organ. The dorsum nasi is the length of the nose. The noon is the tip of the olfactory organ. On either side of the apex, the nostrils are formed by the alae (singular = ala). An ala is a cartilaginous structure that forms the lateral side of each naris (plural = nares), or nostril opening. The philtrum is the concave surface that connects the apex of the nose to the upper lip.

Figure 22.3 Nose This illustration shows features of the external nose (top) and skeletal features of the nose (bottom).

Underneath the thin skin of the nose are its skeletal features (run into Figure 22.three, lower illustration). While the root and bridge of the olfactory organ consist of os, the protruding portion of the nose is composed of cartilage. As a consequence, when looking at a skull, the nose is missing. The nasal bone is one of a pair of basic that lies under the root and bridge of the nose. The nasal bone articulates superiorly with the frontal bone and laterally with the maxillary bones. Septal cartilage is flexible hyaline cartilage continued to the nasal bone, forming the back nasi. The alar cartilage consists of the noon of the olfactory organ; it surrounds the naris.

The nares open up into the nasal cavity, which is separated into left and right sections by the nasal septum (Effigy 22.4). The nasal septum is formed anteriorly by a portion of the septal cartilage (the flexible portion you can bear on with your fingers) and posteriorly by the perpendicular plate of the ethmoid bone (a cranial bone located just posterior to the nasal bones) and the thin vomer basic (whose name refers to its plough shape). Each lateral wall of the nasal crenel has 3 bony projections, called the superior, middle, and inferior nasal conchae. The junior conchae are split up bones, whereas the superior and middle conchae are portions of the ethmoid bone. Conchae serve to increase the surface expanse of the nasal cavity and to disrupt the menses of air equally it enters the nose, causing air to bounce along the epithelium, where information technology is cleaned and warmed. The conchae and meatuses also conserve h2o and preclude dehydration of the nasal epithelium by trapping h2o during exhalation. The floor of the nasal cavity is composed of the palate. The hard palate at the anterior region of the nasal cavity is equanimous of bone. The soft palate at the posterior portion of the nasal cavity consists of muscle tissue. Air exits the nasal cavities via the internal nares and moves into the pharynx.

Figure 22.iv Upper Airway

Several bones that assist form the walls of the nasal cavity accept air-containing spaces called the paranasal sinuses, which serve to warm and humidify incoming air. Sinuses are lined with a mucosa. Each paranasal sinus is named for its associated os: frontal sinus, maxillary sinus, sphenoidal sinus, and ethmoidal sinus. The sinuses produce fungus and lighten the weight of the skull.

The nares and anterior portion of the nasal cavities are lined with mucous membranes, containing sebaceous glands and pilus follicles that serve to forestall the passage of big debris, such as dirt, through the nasal cavity. An olfactory epithelium used to detect odors is institute deeper in the nasal cavity.

The conchae, meatuses, and paranasal sinuses are lined by respiratory epithelium composed of pseudostratified ciliated columnar epithelium (Figure 22.5). The epithelium contains goblet cells, one of the specialized, columnar epithelial cells that produce mucus to trap debris. The cilia of the respiratory epithelium help remove the fungus and debris from the nasal cavity with a constant beating motion, sweeping materials towards the throat to be swallowed. Interestingly, cold air slows the move of the cilia, resulting in aggregating of mucus that may in turn lead to a runny nose during cold atmospheric condition. This moist epithelium functions to warm and humidify incoming air. Capillaries located merely beneath the nasal epithelium warm the air by convection. Serous and mucus-producing cells also secrete the lysozyme enzyme and proteins called defensins, which have antibacterial properties. Allowed cells that patrol the connective tissue deep to the respiratory epithelium provide additional protection.

Figure 22.5 Pseudostratified Ciliated Columnar Epithelium Respiratory epithelium is pseudostratified ciliated columnar epithelium. Seromucous glands provide lubricating fungus. LM × 680. (Micrograph provided past the Regents of University of Michigan Medical School © 2012)

Pharynx

The pharynx is a tube formed by skeletal muscle and lined by mucous membrane that is continuous with that of the nasal cavities (see Figure 22.iv). The pharynx is divided into three major regions: the nasopharynx, the oropharynx, and the laryngopharynx (Effigy 22.6).

Figure 22.half dozen Divisions of the Pharynx The pharynx is divided into 3 regions: the nasopharynx, the oropharynx, and the laryngopharynx.

The nasopharynx is flanked by the conchae of the nasal cavity, and it serves only as an airway. At the top of the nasopharynx are the pharyngeal tonsils. A pharyngeal tonsil, likewise called an adenoid, is an amass of lymphoid reticular tissue similar to a lymph node that lies at the superior portion of the nasopharynx. The function of the pharyngeal tonsil is not well understood, but it contains a rich supply of lymphocytes and is covered with ciliated epithelium that traps and destroys invading pathogens that enter during inhalation. The pharyngeal tonsils are large in children, but interestingly, tend to regress with historic period and may even disappear. The uvula is a small bulbous, teardrop-shaped structure located at the apex of the soft palate. Both the uvula and soft palate move like a pendulum during swallowing, swinging upward to close off the nasopharynx to prevent ingested materials from inbound the nasal crenel. In improver, auditory (Eustachian) tubes that connect to each heart ear cavity open into the nasopharynx. This connection is why colds ofttimes atomic number 82 to ear infections.

The oropharynx is a passageway for both air and nutrient. The oropharynx is bordered superiorly by the nasopharynx and anteriorly by the rima oris. The fauces is the opening at the connection between the oral cavity and the oropharynx. As the nasopharynx becomes the oropharynx, the epithelium changes from pseudostratified ciliated columnar epithelium to stratified squamous epithelium. The oropharynx contains two distinct sets of tonsils, the palatine and lingual tonsils. A palatine tonsil is one of a pair of structures located laterally in the oropharynx in the area of the fauces. The lingual tonsil is located at the base of the tongue. Similar to the pharyngeal tonsil, the palatine and lingual tonsils are composed of lymphoid tissue, and trap and destroy pathogens entering the body through the oral or nasal cavities.

The laryngopharynx is inferior to the oropharynx and posterior to the larynx. It continues the route for ingested cloth and air until its inferior finish, where the digestive and respiratory systems diverge. The stratified squamous epithelium of the oropharynx is continuous with the laryngopharynx. Anteriorly, the laryngopharynx opens into the larynx, whereas posteriorly, it enters the esophagus.

Larynx

The larynx is a cartilaginous construction inferior to the laryngopharynx that connects the pharynx to the trachea and helps regulate the volume of air that enters and leaves the lungs (Figure 22.7). The structure of the larynx is formed by several pieces of cartilage. Three big cartilage pieces—the thyroid cartilage (inductive), epiglottis (superior), and cricoid cartilage (inferior)—grade the major structure of the larynx. The thyroid cartilage is the largest piece of cartilage that makes upwardly the larynx. The thyroid cartilage consists of the laryngeal prominence, or "Adam's apple," which tends to be more than prominent in males. The thick cricoid cartilage forms a band, with a wide posterior region and a thinner inductive region. Iii smaller, paired cartilages—the arytenoids, corniculates, and cuneiforms—attach to the epiglottis and the vocal cords and musculus that assistance move the vocal cords to produce speech.

Figure 22.7 Larynx The larynx extends from the laryngopharynx and the hyoid os to the trachea.

The epiglottis, attached to the thyroid cartilage, is a very flexible slice of elastic cartilage that covers the opening of the trachea (see Figure 22.4). When in the "closed" position, the unattached end of the epiglottis rests on the glottis. The glottis is composed of the vestibular folds, the true song cords, and the space between these folds (Figure 22.8). A vestibular fold, or false vocal cord, is one of a pair of folded sections of mucous membrane. A true song string is ane of the white, membranous folds attached by musculus to the thyroid and arytenoid cartilages of the larynx on their outer edges. The inner edges of the truthful vocal cords are gratis, allowing oscillation to produce sound. The size of the membranous folds of the true vocal cords differs between individuals, producing voices with different pitch ranges. Folds in males tend to exist larger than those in females, which create a deeper vocalisation. The act of swallowing causes the pharynx and larynx to lift upward, allowing the pharynx to expand and the epiglottis of the larynx to swing downward, closing the opening to the trachea. These movements produce a larger area for food to pass through, while preventing nutrient and beverages from entering the trachea.

Figure 22.8 Vocal Cords The true vocal cords and vestibular folds of the larynx are viewed inferiorly from the laryngopharynx.

Continuous with the laryngopharynx, the superior portion of the larynx is lined with stratified squamous epithelium, transitioning into pseudostratified ciliated columnar epithelium that contains goblet cells. Similar to the nasal cavity and nasopharynx, this specialized epithelium produces mucus to trap droppings and pathogens as they enter the trachea. The cilia shell the mucus upward towards the laryngopharynx, where it can be swallowed downward the esophagus.

Trachea

The trachea (windpipe) extends from the larynx toward the lungs (Figure 22.ixa). The trachea is formed by xvi to 20 stacked, C-shaped pieces of hyaline cartilage that are connected by dense connective tissue. The trachealis muscle and elastic connective tissue together form the fibroelastic membrane, a flexible membrane that closes the posterior surface of the trachea, connecting the C-shaped cartilages. The fibroelastic membrane allows the trachea to stretch and expand slightly during inhalation and exhalation, whereas the rings of cartilage provide structural support and prevent the trachea from collapsing. In addition, the trachealis muscle tin be contracted to strength air through the trachea during exhalation. The trachea is lined with pseudostratified ciliated columnar epithelium, which is continuous with the larynx. The esophagus borders the trachea posteriorly.

Figure 22.9 Trachea (a) The tracheal tube is formed past stacked, C-shaped pieces of hyaline cartilage. (b) The layer visible in this cross-section of tracheal wall tissue betwixt the hyaline cartilage and the lumen of the trachea is the mucosa, which is composed of pseudostratified ciliated columnar epithelium that contains goblet cells. LM × 1220. (Micrograph provided past the Regents of University of Michigan Medical School © 2012)

Bronchial Tree

The trachea branches into the correct and left master bronchi at the carina. These bronchi are also lined by pseudostratified ciliated columnar epithelium containing fungus-producing goblet cells (Effigy 22.nineb). The carina is a raised construction that contains specialized nervous tissue that induces violent coughing if a foreign body, such as food, is present. Rings of cartilage, similar to those of the trachea, support the construction of the bronchi and prevent their collapse. The primary bronchi enter the lungs at the hilum, a concave region where blood vessels, lymphatic vessels, and fretfulness also enter the lungs. The bronchi continue to co-operative into a bronchial tree. A bronchial tree (or respiratory tree) is the commonage term used for these multiple-branched bronchi. The main function of the bronchi, like other conducting zone structures, is to provide a passageway for air to move into and out of each lung. In addition, the mucous membrane traps debris and pathogens.

A bronchiole branches from the 3rd bronchi. Bronchioles, which are near 1 mm in bore, further branch until they become the tiny terminal bronchioles, which lead to the structures of gas exchange. At that place are more than chiliad terminal bronchioles in each lung. The muscular walls of the bronchioles practice non comprise cartilage like those of the bronchi. This muscular wall tin can alter the size of the tubing to increment or decrease airflow through the tube.

Respiratory Zone

In dissimilarity to the conducting zone, the respiratory zone includes structures that are straight involved in gas commutation. The respiratory zone begins where the terminal bronchioles join a respiratory bronchiole, the smallest type of bronchiole (Figure 22.10), which and then leads to an alveolar duct, opening into a cluster of alveoli.

Figure 22.10 Respiratory Zone Bronchioles lead to alveolar sacs in the respiratory zone, where gas exchange occurs.

Alveoli

An alveolar duct is a tube composed of polish muscle and connective tissue, which opens into a cluster of alveoli. An alveolus is 1 of the many pocket-sized, grape-like sacs that are fastened to the alveolar ducts.

An alveolar sac is a cluster of many individual alveoli that are responsible for gas exchange. An air sac is approximately 200 μm in bore with elastic walls that allow the alveolus to stretch during air intake, which greatly increases the surface area bachelor for gas exchange. Alveoli are connected to their neighbors past alveolar pores, which help maintain equal air pressure throughout the alveoli and lung (Effigy 22.11).

Figure 22.11 Structures of the Respiratory Zone (a) The alveolus is responsible for gas commutation. (b) A micrograph shows the alveolar structures within lung tissue. LM × 178. (Micrograph provided past the Regents of Academy of Michigan Medical Schoolhouse © 2012)

The alveolar wall consists of iii major cell types: blazon I alveolar cells, type II alveolar cells, and alveolar macrophages. A blazon I alveolar prison cell is a squamous epithelial cell of the alveoli, which institute upwards to 97 percent of the alveolar expanse. These cells are nearly 25 nm thick and are highly permeable to gases. A type Ii alveolar cell is interspersed among the blazon I cells and secretes pulmonary surfactant, a substance composed of phospholipids and proteins that reduces the surface tension of the alveoli. Roaming around the alveolar wall is the alveolar macrophage, a phagocytic cell of the immune system that removes debris and pathogens that have reached the alveoli.

The unproblematic squamous epithelium formed by type I alveolar cells is attached to a thin, elastic basement membrane. This epithelium is extremely thin and borders the endothelial membrane of capillaries. Taken together, the alveoli and capillary membranes form a respiratory membrane that is approximately 0.5 μm (micrometers) thick. The respiratory membrane allows gases to cantankerous by elementary diffusion, assuasive oxygen to be picked up past the blood for send and CO₂ to be released into the air of the alveoli.

Diseases of the…

Respiratory System: Asthma Asthma is common condition that affects the lungs in both adults and children. Approximately eight.2 percent of adults (eighteen.seven meg) and nine.iv pct of children (7 million) in the United States suffer from asthma. In addition, asthma is the most frequent crusade of hospitalization in children.

Asthma is a chronic disease characterized by inflammation and edema of the airway, and bronchospasms (that is, constriction of the bronchioles), which can inhibit air from inbound the lungs. In addition, excessive mucus secretion tin can occur, which further contributes to airway occlusion (Figure 22.12). Cells of the immune arrangement, such as eosinophils and mononuclear cells, may also be involved in infiltrating the walls of the bronchi and bronchioles.

Bronchospasms occur periodically and pb to an "asthma attack." An assail may exist triggered by environmental factors such equally dust, pollen, pet hair, or dander, changes in the weather condition, mold, tobacco smoke, and respiratory infections, or by exercise and stress.

Figure 22.12 Normal and Bronchial Asthma Tissues (a) Normal lung tissue does not have the characteristics of lung tissue during (b) an asthma attack, which include thickened mucosa, increased fungus-producing goblet cells, and eosinophil infiltrates.

Symptoms of an asthma assault involve coughing, shortness of jiff, wheezing, and tightness of the chest. Symptoms of a astringent asthma assault that requires immediate medical attention would include difficulty breathing that results in blue (cyanotic) lips or face, confusion, drowsiness, a rapid pulse, sweating, and severe anxiety. The severity of the condition, frequency of attacks, and identified triggers influence the type of medication that an individual may require. Longer-term treatments are used for those with more than severe asthma. Short-term, fast-acting drugs that are used to treat an asthma set on are typically administered via an inhaler. For immature children or individuals who accept difficulty using an inhaler, asthma medications tin be administered via a nebulizer.

In many cases, the underlying cause of the condition is unknown. Even so, recent research has demonstrated that sure viruses, such as human rhinovirus C (HRVC), and the bacteria Mycoplasma pneumoniae and Chlamydia pneumoniae that are contracted in infancy or early babyhood, may contribute to the development of many cases of asthma.

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