Upper_respiratory_system.pdf

RESPIRATORY SYSTEM (Upper) Figen KAYMAZ, MD, PhD. Prof of Histology and Embryology 1 four discrete events in respiration; 1. Movement of air in and out of the lungs (breathing or ventilation) 2. Exchange of O2 in the inspired air for carbon dioxide in the blood (external respiration) 3. Conveyanc...

RESPIRATORY SYSTEM (Upper) Figen KAYMAZ, MD, PhD. Prof of Histology and Embryology 1 four discrete events in respiration; 1. Movement of air in and out of the lungs (breathing or ventilation) 2. Exchange of O2 in the inspired air for carbon dioxide in the blood (external respiration) 3. Conveyance of O2 and CO2 to and from the cells (transport of gases) 4. Exchange of CO2 for O2 in the vicinity of the cells (internal respiration) 2 Upper respiratory tract Sphenoidal sinus Frontal sinüs Nasal cavity Pharynx Lower respiratory tract Larynx Trachea Bronchi Lungs 3 Functionally the respiratory system is subdivided into two major components: 1. Conducting portion: that conveys air from outside the body to the lungs. which consists of the nasal cavities, nasopharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles 2. Respiratory portion: where exchange of gases between the air and blood occurs. consisting of respiratory bronchioles, alveolar ducts, and alveoli 4 1. The conducting portion; air from the external milieu to the lungs. Extrapulmoner: – Nose (nasal cavity), – Paranasal sinuses – mouth, – nasopharynx, – pharynx, – larynx, These structures not only transport but also filter, moisten, and warm the inspired air before it reaches the respiratory portion of the lungs. – trachea, Intrapulmoner – primary bronchi, – secondary bronchi (lobar bronchi), – tertiary bronchi (segmental bronchi), – bronchioles, – terminal bronchioles. 5 2. Respiratory portion; where gas exchange takes place. Consisting of üRespiratory bronchioles üAlveolar ducts üalveoli 6 The nasal cavity • separated by a nasal septum • Each cavity consists of an external, dilated vestibule and internal nasal cavity. • Skin of the nose enters the nares (nostrils) partway into the vestibule and has sweat glands, sebaceous glands, and coarse, moist vibrissae (hairs) that filter out particulate material from the inspired air. • Within the vestibule, the epithelium loses its keratinized nature and undergoes a transition to typical pseudostratified columnar epithelium before entering the nasal cavities. 7 T. Mucosa of nasal cavity Epithelium:The vestibule, lined by epidermis containing many sebaceous glands, sweat glands, and hair follicles, leads into the nasal (cavity) fossae, which is lined by mucosa consisting of pseudostratified ciliated columnar epithelium interspersed with goblet cells • Lamina propria has important roles in conditioning (warm and humidified) inhaled air. a thick, vascular connective tissue rich in collagen and elastic fibers, attaches firmly to the periosteum and perichondrium of the bony and cartilaginous walls of the nasal cavity, which provide rigidity during inspiration. – Seromucous glands are also found in the LP. thin layer of mucus produced by these glands and the goblet cells also serves to trap particulate and gaseous air impurities that are then removed – Immunoglobulin A (IgA) from plasma cells in the lamina propria is also present in nasal secretions. • 8 • The nasal cavities lie within the skull as two chambers separated by the osseous nasal septum . • Extending from each lateral wall are three bony shelflike projections called conchae. • The middle and inferior conchae are covered with respiratory epithelium ; the roof of the nasal cavities and the superior conchae are covered with specialized olfactory epithelium . 9 Respiratory epithelium • Most of the nasal cavities and the respiratory system’s conducting portion is lined with mucosa having ciliated pseudostratified columnar epithelium known as respiratory epithelium. This epithelium has five major cell types, all of which contact an unusually thick basement membrane. 10 Ciliated columnar cells are the most abundant, each with 250300 cilia on its apical surface Goblet cells are also numerous with basal nuclei and apical domains filled with granules of mucin glycoproteins. Brush cells are a much less numerous, columnar cell type, in which a small apical surface bears sparse, blunt microvilli. Brush cells are chemosensory receptors resembling gustatory cells, with similar signal transduction components and synaptic contact with afferent nerve endings on their basal surfaces. Small granule cells (or Kulchitsky cells) are difficult to distinguish in routine preparations, but possess numerous dense core granules 100 to 300 nm in diameter. Like enteroendocrine cells of the gut, they are part of the diffuse neuroendocrine system. Like brush cells, they represent only about 3% of the cells in respiratory epithelium. Basal cells are mitotically active stem and progenitor cells that 11 give rise to the other epithelial cell types. 12 MEDICAL APPLICATION • The chronic presence or accumulation of toxins that occur with heavy cigarette smoking or industrial air pollution affects the respiratory epithelium beginning in the nasal cavities. Immobilization of the cilia causes failure to clear mucus containing filtered material and exacerbates the problem, leading eventually to the likelihood of squamous metaplasia of the epithelium. A change from pseudostratified ciliated columnar to stratified squamous epithelium can occur, particularly in the mucosa of bronchi. This can produce precancerous cell dysplasia in this tissue. 13 Olfactory Region of the Nasal Cavity • The olfactory chemoreceptors for the sense of smell are located in the olfactory epithelium, a specialized region of the mucous membrane covering the superior conchae at the roof of the nasal cavity. In adult humans, it is about 10 cm2 in area and up to 100 μm in thickness. This thick, pseudostratified columnar epithelium has 3 major cell types. • olfactory epithelium and the underlying lamina propria that houses Bowman's glands and a rich vascular plexus 14 • Olfactory neurons are bipolar neurons present throughout this epithelium. The apical (luminal) pole of each olfactory cell is its dendrite end and has a knoblike swelling with about a dozen basal bodies. From the basal bodies emerge long cilia with nonmotile axonemes for membrane chemoreceptors. These receptors respond to odoriferous substances by generating an action potential along the axons extending from the basal ends of these neurons. The axons leave the epithelium and unite in the lamina propria as very small nerves that then pass to the brain through foramina in the cribriform plate of the ethmoid bone. There they form the olfactory nerve, cranial nerve I, and eventually synapse 15 with other neurons in the olfactory bulb. • Supporting cells are columnar, with broad, cylindrical apexes containing the nuclei and narrower bases. On their free surface are microvilli submerged in a fluid layer. Well-developed junctional complexes bind the supporting cells to the olfactory cells. They help maintain a microenvironment conducive to olfactory function and survival. • Basal cells are small cells near the basal lamina. These are the stem cells for the other two types, replacing the olfactory neurons every 2 to 3 months The lamina propria of the olfactory epithelium possesses large serous glands, the olfactory glands (of Bowman), which produce a constant flow of fluid surrounding the olfactory cilia and facilitating the access of new odoriferous substances. 16 17 18 MEDICAL APPLICATION • The loss or reduction of the ability to smell, anosmia or hyposmia, respectively, can be caused by traumatic damage to the ethmoid bone that severs olfactory nerve axons or by damage to the olfactory epithelium caused by intranasal drug use. • The olfactory neurons are the best-known neurons to be replaced regularly because of regenerative activity of the epithelial stem cells from which they arise. For this reason, loss of the sense of smell due to toxic fumes or physical injury to the olfactory mucosa itself is usually temporary. 19 nasal cavity … nasal septum … cartilaginous ala (wing) of the nose … naris (nostril) … choana … Nasal conchae; • three bony shelflike projections on each lateral wall • In LP large venous plex – swell bodies– the superior (olfactory epithelium), – middle, – inferior 20 HISTOLOGY OF THE NASAL CAVITIES AND PARANASAL SINUSES • Nasal cavity … posteriorly choana … nasopharynx. Nasal conchae Epithelium: consisting of bony trabeculae covered by mucous membrane. (pseudostratified ciliated columnar epithelium ) abundant, mucus-secreting goblet cells. Lamina propria: Many branched seromucous glands extensive, tortuous network of venous sinuses, arteriovenous anastomoses, and capillaries Paranasal sinuses Epithelium: lower than the nasal cavities, with fewer goblet cells. Three types of cells characterize the respiratory epithelium: basal, ciliated, and goblet cells. 21 • Nasal bleeding usually occurs from Kiesselbach's area, the anteroinferior region of the nasal septum, which is the site of anastomosis of the arterial supply of the nasal mucosa. 22 Paranasal sinuses 1. 2. 3. 4. frontal, ethmoidal, sphenoidal, Maxillary air-filled bilateral cavities that communicate with nasal cavities. They are lined with a thinner respiratory epithelium with fewer goblet cells. The lamina propria contains only a few small glands and is continuous with the underlying periosteum. The paranasal sinuses communicate with the nasal cavities through small openings; mucus produced there is moved into the nasal passages by the activity of the ciliated epithelial cells. 23 STRUCTURE OF THE NASAL CAVITIES AND PARANASAL SINUSES Sinusitis is a common clinical condition referring to inflammation of the mucous membrane of the sinuses 24 HISTOLOGY OF THE NASAL CAVITIES AND PARANASAL SINUSES 25 Nasopharynx The nasal cavities open posteriorly into the nasopharynx (First part of the pharynx), continuing caudally with oropharynx (1) the superior nasopharynx, lined by a respiratory epithelium, pharyngeal tonsil, (2) the middle oral pharynx, stratified squamous epithelium (3) the inferior laryngeal pharynx, stratified squamous epithelium, the bilateral openings of the auditory tubes connected to each middle ear cavity. lamina propria is composed of a loose to dense, irregular type of vascularized connective tissue housing seromucous glands and lymphoid elements. 26 LARYNX • a short (4 cm × 4 cm) passage for air between the pharynx and the trachea. Its rigid wall is reinforced by hyaline cartilage (in the thyroid, cricoid, and the inferior arytenoid cartilages) and smaller elastic cartilages (in the epiglottis, cuneiform, corniculate, and the superior arytenoid cartilages), all of which are connected by ligaments. In addition to maintaining an open airway, movements of these cartilages by skeletal muscles participate in sound production during phonation. 27 HISTOLOGY OF THE EPIGLOTTIS • • • • covers the entrance to the larynx. a flattened structure projecting from the upper rim of the larynx, serves to prevent swallowed food or fluid from entering that passage. a core of elastic cartilage, attaches to the hyoid bone. Epithelium: – lingual surface is covered by a nonkeratinized stratified squamous epithelium that is directly continuous with the epithelium covering the dorsal surface of the tongue. – laryngeal surface is covered pseudostratified ciliated columnar epithelium with goblet cells, commonly known as respiratory epithelium. Lamina propria : – loose connective tissue – seromucous glands 28 – elastic cartilage 29 HISTOLOGY OF THE EPIGLOTTIS 30 HISTOLOGY OF THE LARYNX AND VOCAL CORDS epiglottis provides a cover over the laryngeal aditus (opening). • lumen of the larynx is characterized by two pairs of shelf-like folds 1. vestibular folds: the superiorly positioned immovable (false folds) – respiratory epithelium overlying seromucous glands and lymphoid nodules. 2. vocal folds: the inferiorly placed folds, vocal folds (cords), vocalis muscle, nonkeratinized stratified squamous ep (important for phonation or sound production) • 31 32 • Folds are covered with stratified squamous epithelium that protects the mucosa from abrasion and desiccation from rapid air movement. • A dense regular bundle of elastic connective tissue, the vocal ligament, supports the free edge of each vocal fold. • Deep to the mucosa of each vocal fold are large bundles of striated fibers that comprise the vocalis muscle. • space between the vocal folds (the rima glottidis) 33 34 • During silent respiration, the vocal folds are partly abducted (pulled apart), and during forced inspiration, they are fully abducted • During phonation, however, the vocal folds are strongly adducted (drawn together), forming a narrow interval between them. The movement of air against the edges of the strongly adducted vocal folds produces and modulates sound (but not speech, which is formed by movements of the pharynx, soft palate, tongue, and lips) 35 Larynx • The larynx is lined by pseudostratified ciliated columnar epithelium, except on the superior surfaces of the epiglottis and vocal folds, which are covered by stratified squamous nonkeratinized epithelium. • The cilia of the larynx beat toward the pharynx, transporting mucus and trapped particulate matter toward the mouth to be expectorated or swallowed 36 37