Lecture 16, 17 & 18: Respiratory System Anatomy & Histology PDF

Lecture 16, 17 & 18 Respiratory System Anatomy & Histology Learning outcomes The student should be able to: Identify and describe the paranasal air sinuses, pharynx and larynx. Write notes on the trachea and the pleural sac. Describe the external appearance of the lungs, including the...

Lecture 16, 17 & 18 Respiratory System Anatomy & Histology Learning outcomes The student should be able to: Identify and describe the paranasal air sinuses, pharynx and larynx. Write notes on the trachea and the pleural sac. Describe the external appearance of the lungs, including the surface markings, surface features, borders and fissures. Describe the internal appearance and components of the bronchial tree as well as naming the respiratory unit. Explain what the mediastinum is, and give a brief description of the superior and inferior mediastinum. Annotate a diagrammatic representation of the above-mentioned aspects Understand the histological features of the nasal cavity To know the layers that form the trachea, bronchus and bronchiole To understand the differences between the three tubular structures To know the histological features of the lungs, including the cellular detail 2  Respiratory System The respiratory tract consists of: – Upper respiratory tract – above larynx – Lower respiratory tract – below larynx Functions: I. Provides extensive gas exchange surface area between air and circulating blood II. Moves air to and from exchange surfaces of lungs III.Protects respiratory surfaces from outside environment IV. Produces sound V. Participation in olfactory sense 3  Nasal cavity Nose Upper respiratory tract: UPPER Pharynx nose, nasal cavity, and pharynx RESPIRATORY SYSTEM LOWER Larynx RESPIRATORY Trachea SYSTEM Bronchus Bronchioles Lower respiratory tract: larynx, trachea, bronchial tree, and alveoli. RIGH RIGHT LEFT T LUNG LUNG LUNG 4  Upper Respiratory Tract Nasal Cavity – 2 elongated, wedge-shaped spaces; uppermost part of respiratory tract & contain olfactory receptors – Held open by framework of bone & cartilage – Anterior region: smaller, enclosed by external nose – Posterior region: larger, located centrally within skull – Openings: nares - anterior, choanae – posterior – Nasal cavities are separated from: Each other by a midline nasal septum Oral cavity below by the hard palate Cranium by parts of frontal, ethmoid & sphenoid bones – Each cavity has a floor, roof, medial wall & lateral wall 5  Roof Medial Wall Choanae Lateral Wall Nasal septum Floor Nares Nasal bones Nasal In addition to receptors for the cartilages sense of smell (olfaction), nasal cavities adjust the temperature and humidity of respired air, and trap and remove particulate matter Nares from the airways. 6  Upper Respiratory Tract Nasal Cavity Air enters the nose’s two nares (nostrils). The nasal bones superiorly and the plates of hyaline cartilage at the end of the nose are responsible for the shape of the nose. The nasal septum (ethmoid bone – superiorly, vomer – inferiorly, septal cartilage – anteriorly) divides the nasal cavity into right and left chambers, each with a roof, floor (hard palate), smooth medial wall (septum), and a ridged lateral wall. The anterior part of the nasal cavity (the vestibule) has stiff hairs (vibrissae) which filter particles from the air. The nasal cavity widens posterior to the vestibule to make room for 3 bony ridges called nasal conchae. –The ethmoid bone forms the superior and middle conchae, while the inferior conchae is a separate bone. –The conchae increase the surface area of the nasal cavity and also cause turbulence and this contributes to the humidification, warming and filtration of air. Olfactory neurons, located in the roof the nasal cavity, detect odours and provide the sense of smell. 7  Roof Vestibule Nasal Conchae Functions: (1) increase surface area middle of contact between cavity wall and inspired air (2) cause air turbulence inferior and thus deflect airflow across the mucosal surface. Nares Floor Choanae 8  Upper Respiratory Tract Nasal Cavity Each nasal cavity consists of 3 general regions: the (i) nasal vestibule, (ii) the respiratory region, and the (iii) olfactory region. (i) The nasal vestibule is a small dilated space just internal to the naris and it is lined by skin and contains hair follicles. (ii) The respiratory region is the largest part of the nasal cavity, has rich neurovascular supply, and is lined by respiratory epithelium composed mainly of ciliated and mucous cells. (iii) The olfactory region, located at the apex of each nasal cavity, is small and contains olfactory receptors. 9  Upper Respiratory Tract Paranasal Sinuses – The paranasal sinuses are air-containing cavities in the facial bones & are connected to the nasal cavity – 4 paranasal sinuses, each named according to the bone in which they are found: 1. Ethmoid: cluster of air cells in ethmoid bone 2. Frontal: two, triangular & most superior 3. Maxillary: largest, clinically more significant 4. Sphenoidal: two, posterior & inferior to nasal cavity Functions: I. make the skull lighter II. enhance voice resonance 10 (a) Anterior aspect (b) Lateral aspect Frontal sinus Frontal Ethmoidal sinus air cells Ethmoidal (sinus) air cells Sphenoid Sphenoid sinus sinus Maxillary Maxillary sinus sinus Frontal sinuses Ethmoid sinuses Sphenoidal sinuses 11 Maxillary sinuses  Sinusitis Inflammation of the epithelium in the sinuses (sinusitis) causes increased mucus production, and the accompanying swelling may block the drainage channels (called ostia) to the nasal cavities. The accumulation of mucus causes pressure to build up in the sinus, causing a sinus headache. Decongestants (vasoconstrictor drugs) help to reduce swelling, thereby improving mucus drainage which reduces pressure in the sinus. Maxillary Sinus The maxillary sinus, the largest and lowest sinus, is clinically important: (1) As its drainage orifice lies superiorly near the roof of the sinus, the maxillary sinus does not drain well and sinusitis develops more easily. (2) Furthermore, the upper Maxillary molars are separated by a thin plate of bone sinus from the floor of the sinus, and sinusitis can lead to dental pain from healthy teeth or spread of infection from teeth to the sinus e.g. following tooth extraction. 12  Upper Respiratory Tract Pharynx – A musculofascial half-cylinder linking oral & nasal cavities in the head, to the larynx & oesophagus located in the neck – Common pathway for air (respiratory) & food (GIT) 3 Parts: I. Nasopharynx: superior portion, behind nasal cavity II. Oropharynx: middle portion, behind oral cavity III.Laryngopharynx: inferior portion, extends into larynx & oesophagus 13  Pharynx Pharyngeal tonsil Auditory tube opening Nasopharynx Nasopharynx Oropharynx Oropharynx Air Laryngopharynx Laryngopharynx Palatine tonsil Food Oesophagus Lateral View Trachea Posterior View The pharyngeal wall is formed by skeletal muscles. Gaps between the muscles are reinforced by fascia. 14  Lower Respiratory Tract Larynx – A roughly cylindrical cartilaginous tube, between pharynx above & the trachea below – The larynx is a valve (or sphincter) to close the lower respiratory tract, and a resonance chamber to produce sound – Composition: 3 large unpaired cartilages: epiglottis, thyroid & cricoid 3 small paired cartilages: arytenoid, corniculate & cuneiform A fibroelastic membrane & numerous intrinsic muscles – The larynx is suspended from the hyoid bone above & attached to the trachea below by membranes & ligaments 15  Epiglottis Hyoid bone Larynx Thyroid cartilage Functions of the Larynx: Cricoid cartilage (1) Provides a patent airway (2) Routes air and food into Trachea proper channels (3) Voice production 16  Right lamina Left lamina Thyroid cartilage Superior horn A hyaline cartilage that forms the anterior and lateral walls of larynx. Anteriorly, its two Inferior laminae project forward as the Laryngeal prominence horn laryngeal prominence (Adam’s apple), posteriorly it is incomplete. It is attached to the hyoid bone, epiglottis and other laryngeal cartilages by ligaments. 17  Anterior surface Posterior surface Epiglottis of epiglottis of epiglottis A leaf-shaped flap of elastic cartilage that is attached by its stem to the posterior surface of the thyroid cartilage. During swallowing, the larynx is elevated and the epiglottis folds back to close off the larynx, thus it prevents entry of food and fluids into the respiratory tract. 18  Cricoid Cricoid cartilage cartilage A complete ring of hyaline cartilage that forms the inferior portion of the larynx. Ligaments attach the cricoid to the 1st tracheal cartilage below. It articulates with arytenoid cartilages above. Function: keeps the tracheal entrance open. lamina 19  Arytenoid cartilages Muscular process Arytenoid The two arytenoid cartilages are cartilage pyramid-shaped, and are located on the superior surface of the cricoid cartilage. Each has an apex and base, and two processes: a vocal process and a muscular process. Function: they open and close the Vocal process laryngeal opening (glottis). Corniculate cartilages Two small cartilages attached to the Cuneiform cartilages apices of the arytenoid cartilages. Corniculate cartilages Cuneiform cartilages Two small elongated cartilages that lie within folds between arytenoid cartilages and the epiglottis. 20  Respiratory System Laryngeal Ligaments – Ligaments & folds bind together laryngeal cartilages E.g. thyrohyoid, cricothyroid, cricotracheal, aryepiglottic – Vestibular & vocal ligaments: extend between thyroid cartilage and arytenoid cartilages; covered folds of laryngeal epithelium called vestibular & vocal folds Vestibular ligaments: lie within vestibular folds above vocal ligaments; protect delicate vocal folds Vocal ligaments: vibrate the vocal folds which cover it; produce sound waves >> sounds varied by tension of vocal folds Laryngeal Muscles – Extrinsic muscles: from neck & pharynx; position & stabilize the larynx – Intrinsic muscles: small, control tension of vocal folds & opening or closing of glottis (opening of larynx) 21  Thyrohyoid membrane Thyrohyoid ligament Vestibular ligament Vocal Cricothyroid ligament ligament Cricotracheal ligament Intrinsic muscles 22  Corniculate cartilage Glottis (closed) Glottis (open) Intrinsic muscles change vocal fold tension. Vestibul ar fold Vocal fold Epiglotti s Root of tongue 23  Lungs Lungs Extend from just above the clavicle down to the Diaphragm Muscle –Apex –Base –Root (hilum) of the lung Location where primary bronchus, bronchial artery, pulmonary artery, pulmonary veins, lymphatic vessels, and nerves enter and leave the lung Mediastinum- area between the lungs Diaphragm muscle 3 large openings for – Esophagus – Aorta – Inferior vena cava Diaphragmatic hernia is a defect in which there is an abnormal opening in the diaphragm (CDH and ADH) 24 Mediastinum 25  Gross Anatomy of Lungs Base, apex (cupula), costal surface, cardiac notch Oblique & horizontal fissure in right lung results in 3 lobes Oblique fissure only in left lung produces 2 lobes Cardiac notch (impression) – cavity that accommodates the heart 26 Mediastinal Surface of Lungs 27  Pleurae The pleural membranes consists of mediastinum simple squamous epithelium that »Two lateral secret a slippery serous fluid compartments, each containing a Thin, double-layered serosa lung –Parietal pleura Covers the thoracic wall and –Pleural cavity-fluid filled space superior face of the between the pleural membranes diaphragm Pleural Effusion Continues around heart and between lungs –Visceral, or pulmonary pleura Covers the external lung surface Divides the thoracic cavity into three chambers »The central 28  Respiratory (Pulmonary) tree Primary bronchus (enters each lung) Secondary (lobar) bronchi Tertiary (Segmental) bronchi Bronchioles Alveolar Ducts with Alveoli (air sacs) 1. With each subdivision, there is progressively: –Less cartilage –More elastic cartilage –More visceral smooth muscle 2. The bronchioles are innervated by autonomic motorneurons - bronchoconstriction - bronchodilation 3. There are about 300 million alvioli in each lung 29  Trachea Tracheotomy- surgical opening of the trachea [tomy means to Cut] –an incision in the windpipe made to relieve an obstruction to breathing Tracheostomy- an opening in the trachea [stomy means opening] 30  Respiratory Tract Histology Basic Structure & Function – two main components: conducting & respiratory Conducting portion – nasal cavities, pharynx, larynx, trachea, bronchi & bronchioles; main function is to ‘condition’ inspired air Respiratory portion – respiratory bronchioles, alveolar ducts, alveolar sacs & alveoli; for gas exchange between blood & air Consists of four main layers: 1. Mucosa: epithelium & lamina propria 2. Submucosa: dense irregular CT & glands 3. Cartilage and/or muscular layer 4. Adventitia 31  Pseudostratified columnar Basement membrane epithelium & goblet cells MUCOSA Blood vessel Lamina propria SUBMUCOSA Glands in submucosa Perichondrium Chondrocytes CARTILAGE or in hyaline MUSCLE LAYER cartilage Perichondrium ADVENTITIA Loose CT Conducting Zone The components of the four layers vary in different regions Respiratory Zone of the respiratory tract according to the functions of each part. 32  Nasal Cavities The vestibules are lined with stratified squamous epithelium.. The respiratory region has pseudostratified ciliated columnar epithelium, goblet cells and mucous and serous glands in the lamina propria which supplement goblet cells secretions. The superior part is lined with olfactory epithelium consisting of olfactory cells and supporting cells. Olfactory epithelium Basal cell Stratified squamous epithelium Pseudostratified columnar epithelium Olfactory receptor cell Supporting cell 33  Pharynx & Larynx Depending on the extent of abrasive forces on the epithelium, the pharynx is lined with either respiratory epithelium (nasopharynx), or with a stratified squamous epithelium (oropharynx and laryngopharynx). Pharyngeal tonsils (adenoids) are present in the posterior and upper regions of the nasopharynx. Nasopharynx Stratified squamous epithelium Oropharynx and laryngopharynx Stratified squamous epithelium covers the epiglottis and upper half of larynx subject to wear and tear including vocal cords. The rest Larynx (lower part) of the laryngeal epithelium is pseudostratified Pseudostratified ciliated columnar epithelium ciliated columnar. 34  The trachea is lined with respiratory epithelium with Trachea variable goblet cells. The lamina propria consists of loose CT and the submucosa contains mucoserous glands. The submucosa ends with the perichondrium of the tracheal cartilages. The free posterior ends of the cartilages are connected by bands of smooth muscle (trachealis muscle). Trachea Tracheal cartilage s RIGHT LEFT LUNG 35 LUNG  Bronchi At the transition from bronchi to bronchioles the epithelium changes to simple ciliated columnar then to simple cuboidal. Glands and cartilage are absent , and a layer of smooth muscle is relatively thicker than in the bronchi. Bronchi have rings of cartilages that support the tubes and pseudostratified columnar epithelium. The cartilages give way to irregular and discontinuous plates of cartilages in the smaller bronchi. As the bronchi enter the Bronchioles lungs, spiral strands of smooth muscle appear around the airway. 36  Respiratory bronchiole Alveoli Alveolar Alveolar sac duct Acinus Respiratory bronchioles give rise to alveolar ducts and alveoli. As the number of alveoli increases, they form alveolar sacs and together with alveolar ducts they form an acinus. Alveolar ducts and sacs have patches of simple cuboidal epithelium. Alveoli have simple squamous epithelium. 37  Alveolar Epithelium Red blood cell Alveolar pores Capillary O2 Capillary Type I cell CO2 of alveolar wall Alveolus Macrophage Alveolus Alveolar epithelium Fused basement membranes of the Respiratory alveolar epithelium Red blood cell membrane and the capillary Alveoli (gas-filled in capillary Type II (surfactant- endothelium air spaces) secreting) cell Capillary endothelium Alveolar epithelium contains 3 major cell types: (1) type I pneumocytes – squamous for gas exchange (most abundant, >97% of surface), (2) type II pneumocytes – rounded cells secrete surfactant, and (3) alveolar macrophages (dust cells) – remove foreign materials. 38 In terminal and Respiratory bronchiole Alveolar duct respiratory bronchioles, Smooth muscle Alveolus smooth muscle fibres are Alveolar oriented in spiral fashion Elastic fibres sac while elastic fibres are longitudinal. Alveolar pore Capillaries (of Kohn) The basic structure of a portion of a single lobule. A network of capillaries, supported by elastic fibres, surrounds each alveolus. Respiratory bronchioles are also wrapped by smooth muscle cells that can change the diameter of these airways. Pneumocyte Pneumocyte type II type I Alveolar Red blood cell macrophage Alveolar pores (of Kohn), Elastic fibres Capillary lumen Capillary Nucleus of which connect adjacent endothelium endothelial cell alveoli, are responsible 0.5 for collateral respiration μm when blockage of a small bronchiole occurs. Alveolar macrophage Fused basement Alveolar Surfactant epithelium membrane Capillary Alveolar air space The respiratory membrane, Endothelial which consists of an alveolar cell of capillary epithelial cell, a capillary endothelial cell, and their fused basement membranes. A diagrammatic view of alveolar structure. A single capillary may be involved in gas exchange with several alveoli simultaneously. 39 1. Ciliated epithelium 2. Goblet cell 3. Gland 4. Cartilage 5. Smooth muscle cell 6. Clara cell 7. Capillary 8. Basal membrane 9. Surfactant 10. Type I pneumocyte 11. Alveolar septum 12. Type II pneumocyte 40 Notes & Figures Adapted From: 1. Gray’s Anatomy for Students – Drake et al. (2005) 2. Fundamentals of Anatomy & Physiology – Martini et al. (9th Edition) 3. Anatomy & Physiology – Seeley et al. (7th Edition) 4. Histology & Cell Biology – Kierszenbaum (2002) 5. Atlas of Human Anatomy – Frank Netter 41