BMS 250 Lung Anatomy PDF

Lung Anatomy BMS 250 Learning Outcomes Describe the embryological development of the respiratory system. Relate development of the lung to tracheoesophageal fistula & IRDS Identify surface anatomical landmarks of the pleurae Describe the structure of various components of the thoracic wall...

Lung Anatomy BMS 250 Learning Outcomes Describe the embryological development of the respiratory system. Relate development of the lung to tracheoesophageal fistula & IRDS Identify surface anatomical landmarks of the pleurae Describe the structure of various components of the thoracic wall, highlighting contributions to the movements of ventilation and the compliance of the chest wall Describe anatomical landmarks, blood supply, lymphatic drainage, and innervation of the lungs Identify the structures and functions of constituents of the upper and lower airways Describe the histology of the olfactory and respiratory epithelium Pre-Assessment During embryological development, which structure gives rise to the lungs? A. Pharyngeal pouches B. Foregut C. Mesodermal Somites D.Neural Tube Pre-Assessment In which body cavity are the lungs located? A. Peritoneum B. Pericardial C. Pleural D. Pharyngeal The Beginning… Bilaminar disc: epiblast, hypoblast Gastrulation: bilaminar disc à trilaminar disc § Formation of the primitive streak § Cells from the epiblast move toward the primitive streak and through it § As cells migrate, they differentiate into different layers Trilaminar disc: ectoderm, mesoderm, endoderm The Beginning… Lateral Folding: Cranio-caudal Folding: Lateral Plate Mesoderm The lateral plate mesoderm splits into: § The parietal (somatic) layer § The visceral (splanchnic) layer Endoderm: epithelial lining & glands Splanchnic layer: muscles, cartilage, & connective tissue Main Components Lungs Trachea Larynx Pleura Formation of the Lung Buds At 4 weeks, respiratory diverticulum (lung buds) appear on the ventral wall of the foregut & § Development is dependent on increased retinoic acid and TBX4 transcription factor * Endodermal Origin: Epithelium of internal lining in larynx, trachea, bronchi, and lungs Splanchnic Mesodermal Origin: Cartilaginous, muscular, and connective tissue components of the trachea and lungs - buds on lung tral wall ren of foregut Lung Bud & Foregut Connections As the lung bud expands caudally, two longitudinal ridges, tracheoesophageal ridges, develop Subsequent fusion of tracheoesophageal ridges forms the tracheoesophageal septum > Days 26 to 28: First bifurcation of lung buds, forming right and left primary bronchial buds. Tracheoesophageal septum Tracheoesophageal ridges Days 26-28) Primary bronchial buds Esophageal Atresia & Tracheoesophageal Fistula Atresia: Proximal esophagus does not connect with the distal part, r a i s ee ~ creating a blind-ending tube Tracheoesophageal Fistula: Connection (fistula) between the trachea and the esophagus, which may result from abnormal development in utero. Atresia /fistula Case Study… A newborn struggling to breathe, turning blue shortly after birth. The clinical team discovers that the child is not able to properly swallow or have liquids. Can you guess what might be happening? Esophageal Atresia & Tracheoesophageal Fistula Trachea, Bronchi, Lungs 5th week: Each primary bronchial bud enlarges. § Right bronchus bud & left bronchus bud Sa Right primary bronchus forms three secondary bronchi. Left primary bronchus forms two secondary bronchi Remember primitive body cavities? Lung growth in caudal and lateral directions leads to the expansion into the body cavity. Spaces for the lungs are initially narrow pericardioperitoneal canals. Pleuroperitoneal and pleuropericardial folds ultimately separate pericardioperitoneal canals from peritoneal and pericardial cavities. § The remaining spaces form primitive pleural cavities Mesoderm covering the ~ outside of the lung develops into visceral ice pleura. The somatic mesoderm layer covering the body wall from the inside becomes parietal pleura. m The space between the parietal and visceral pleura is the pleural cavity. Remember primitive body cavities? Further Development… Secondary bronchi divide repeatedly. § Form 10 tertiary (segmental) bronchi in the right lung and 8 in the left. § Tertiary bronchi create bronchopulmonary segments in the adult lung. By the end of 24 weeks, approximately 17 rounds min of subdivisions take place. § An additional six divisions occur during postnatal life. Maturation of the Lungs 4 Stages: 1. Pseudoglandular stage (5 – 16 wks) Branching has continued to form terminal bronchioles. 2. Canalicular stage (16 – 26 wks) Each terminal bronchiole divides into two or more respiratory bronchioles, which in turn divide into three to six alveolar ducts. 3. Terminal sac period aka Saccular (26 wks – birth) Terminal sacs (primitive alveoli) form, and capillaries establish close contact. 4. Alveolar period (36 wks – 8 yrs) Mature alveoli have well-developed epithelial–endothelial (capillary) contacts. What’s Next? Up to 7th month: § Bronchioles continuously divide into smaller canals. § Vascular supply steadily increases. § Terminal bronchioles divide into respiratory bronchioles. 34 Each respiratory bronchiole divides into three to six alveolar ducts. - § Alveolar ducts end in terminal sacs, also known as primitive alveoli. § Flat alveolar cells surround the sacs, in close contact with neighboring capillaries End of 7th month: § Sufficient numbers of mature alveolar sacs and capillaries are present. Type I & Type II Alveolar Epithelial Cells Cells lining the sacs, type I alveolar epithelial cells, become thinner. § Surrounding capillaries protrude into alveolar sacs, forming the blood–air barrier. At the end of 24 weeks, type II alveolar epithelial cells develop. § These cells produce surfactant, a phospholipid-rich fluid lowering surface tension at the air–alveolar interface. Fetal Breathing Movements Begin before birth, causing theraise aspiration of amniotic fluid. Essential for stimulating lung development and conditioning respiratory muscles. At birth, most lung fluid is rapidly resorbed by blood and lymph capillaries. Surfactant remains deposited as a thin phospholipid coat on alveolar cell membranes. am § With air entering alveoli during the first breath, surfactant prevents the development of a high surface tension and collapse of alveoli. - Infant Respiratory Distress Syndrome (IRDS) Formerly known as hyaline membrane disease. Insufficient surfactant leads to high surface tension, risking alveolar collapse during expiration. - - § Common cause of death, accounting for approximately 20% of newborn deaths. Larynx The internal lining of the larynx originates from the endoderm. Cartilages and muscles of the larynx originate from mesenchyme of the fourth and sixth pharyngeal arches. § Mesenchyme of the fourth and sixth pharyngeal arches transforms 4 into thyroid, cricoid, and arytenoid cartilages. The rapid proliferation of mesenchyme changes the laryngeal orifice's appearance. Larynx As cartilages are formed, laryngeal epithelium occludes the lumen. § Subsequent vacuolization and recanalization processes produce lateral recesses known as the laryngeal ventricles. * Tissue folds surrounding the ventricles differentiate into the false and true vocal cords. [ All laryngeal muscles are innervated by branches of the 10th cranial nerve, the vagus nerve (CN X). 3 References Sadler TW. Respiratory System. In: Langman’s Medical Embryology. 14th ed. Wolters Kluwer; 2023.  Landmarking Pleurae Visceral Pleura à attached to the lung Parietal Pleura à lines the internal thoracic cavity - Visceral & Parietal Pleurae à Pleural sac * Line Parietal Layer Visceral Layer Rib Level Rib Level Midclavicular 6 8 Midaxillary 8 10 Medial Edge of 10 12 Scapula Parietal Pleura Mediastinal Parietal Pleura: Lines the lateral surface of the mediastinum. - - Costal Parietal Pleura: Lines the internal surface of the ribs. - Diaphragmatic Parietal Pleura: Lines the superior surface of the diaphragm. - - Cervical Parietal Pleura (Cupula): Extends above rib 1 to the root of the neck. - - - Innervation: general sensory neurons (sensitive to pain). § Intercostal nerves innervate the parietal pleura lining the peripheral portion of the diaphragm and the ribs. § Phrenic nerves innervate the parietal pleura lining the central portion of the diaphragm and the mediastinum. Visceral Pleura Follows the contour of the lobes. § Contiguous with the parietal pleura at the hilum of each lung. Along with the parietal pleura, produces and reabsorbs pleural fluid. § The bulk of pleural fluid clearance is performed by lymphatics in the parietal pleura. - -m Innervated by visceral sensory neurons (insensitive to pain). § Innervation is provided by the autonomic vagus nerve (CN X). Both pleural layers have simple squamous mesothelium.D - men Pleural Space Located between parietal and visceral pleurae. A thin film of the pleural fluid in the pleural space. §- Lubricates and facilitates gliding movement of the lungs during breathing. § Surface tension of pleural fluid ensures adherence of parietal and visceral pleurae. W Resists lung collapse. U Pleural pressure is slightly less than atmospheric pressure. § Result of opposing elastic forces of the chest wall and lung. § Referred to as "negative me pressure.” Pneumothorax Occurs due to air entering the pleural space, often from chest trauma. § Breaks the coupling between parietal and visceral pleura. Leading to an equalization between pleural pressure and atmospheric pressure. - § Results in a collapsed lung. Hemothorax: Blood fills the pleural space.  Pleural Recesses Lung does not fill the entire pleural sac during quiet respiration. § Areas with incomplete filling are called pleural recesses. Pleural fluid accumulates here during quiet breathing. During deep breaths, expanded lungs push into recesses. & 35 § Costodiaphragmatic Recess § Costomediastinal Recess Q. Where would you insert a needle to remove blood during a hemothorax? Back to the Lungs… Pyramid-shaped: § Apex § Base Surfaces (3): [] § Costal § Diaphragmatic § Mediastinal Borders (3): [] § Anterior § Posterior § Inferior Lobes of the Lung Right Lung: § Three lobes: superior, middle, and inferior. § Two fissures: horizontal and oblique - - - § Shorter and wider than the - left. Left Lung: § Two lobes: superior and inferior. § One fissure: oblique § Cardiac notch and lingula Why are lungs great dancers? They are groovyyy! Subclavian Artery Azygous vein Hilum of the Lung The location where blood vessels, air passages, lymphatics, and nerves enter and leave the lungs. §[Connection between themmm lung and the cardiovascular system. Parietal and visceral pleura meet à pulmonary ligament Blood Supply to the Lung Dual circulation: § Bronchial Circulation: Supplies oxygenated blood to the bronchial tree Systemic circulation – branch of aorta * Three bronchial arteries: 2 to left, 1 to right num Drain into bronchial veins & pulmonary veins § Bronchial veins à azygous § Pulmonary Circulation: Circulation of deoxygenated blood from the heart to the lungs, and oxygenated blood back to the heart from the lungs  Lymphatic Drainage of the Lung Collecting lymphatic vessels in the lung in the interlobular septa that define lung lobules. Lymph from lung lobes drains into pulmonary and bronchopulmonary (hilar) nodes. Continues into tracheobronchial (carinal) nodes and paratracheal nodes. Lymph enters the systemic circulation through: Right Lung: Right lymphatic duct. paratracheal noder Left Lung: Thoracic duct. lymph a Tracheobronchit noderly a pulmonary ↳ bronchopulmonary Chilar) nodes (ALYMPH-BPTP & (to remember) Innervation of the Lungs Pulmonary Plexus: § Follows the trachea and bronchial tree. - i a § Provides both parasympathetic and sympathetic innervation. Parasympathetic: § Supplied by branches of the vagus nerve (CN X). § Causes bronchoconstriction and bronchial gland secretion. Sympathetic: § Supplied by postganglionic sympathetic fibers from T1–T4 sympathetic ganglia and cervical sympathetic ganglia. § Causes bronchodilation and inhibition of bronchial gland secretion. § Visceral sensory fibers from the visceral pleura and bronchi - accompany sympathetic fibers. - § Primary control is epinephrine from the adrenal gland. -- Bronchial Tree 1. Trachea 2. Primary bronchi 3. Secondary bronchi 4. Tertiary bronchi 5. Conducting bronchioles 6. Terminal bronchioles 7. Respiratory bronchioles 8. Alveoli Bronchial Tree exchange) air transport (NO gas > - Conducting airways include trachea, primary bronchi, secondary bronchi, and tertiary bronchi. Trachea: § Begins at cricoid cartilage, descends into thorax, bifurcates into - i s right and left primary bronchi at T4–T5 vertebral level. A - § Wall consists of C-shaped rings of hyaline cartilage closed - posteriorly by the trachealis muscle. - § Carina: Internal ridge at tracheal bifurcation into primary bronchi. si - Q. Why do we have the trachealis muscle and not cartilage be able to all around? - > to up cough things Bronchial Tree Right primary bronchus: vein azygous [ J § Divides into superior, middle, and inferior I left pam secondary bronchi. rtery ⑨ § Shorter, wider, and more vertical than the left primary bronchus. - § Azygos vein arches over the right primary - bronchus before entering the SVC. - Left primary bronchus: S § Divides into superior and inferior secondary bronchi. J Q. If you aspirate § Left pulmonary artery arches over the left - a foreign body, primary bronchus. - where is likely to Secondary bronchi divide into tertiary bronchi. go?-right pulmonary bronchiole § Tertiary bronchi divide into bronchioles that vertical terminate in alveolar sacs. be more + shorter + wider Bronchopulmonary Segments A bronchopulmonary segment is a region of the lung supplied by a tertiary (segmental) bronchus. - § Each segment has branches of the pulmonary artery and vein. § They are district anatomical, functional, and surgical units. Respiratory Tracts Nasal Cavities Two cavernous chambers within the skull, separated by the osseous nasal septum. § Covered by mucosa with lamina propria and bony projections3 [ called conchae on the lateral walls. inse Blood flow counteracts the direction of inspired air, releasing heat to warm and humidify the air. Water secreted from small seromucous glands aids in humidification. - Thin mucus layer produced by glands and goblet cells traps and removes inhaled particles. Immunoglobulin A from plasma cells in the lamina propria helps inactivate microorganisms. - [Middle and inferior conchae 3have respiratory epithelium.x - The roof of nasal cavities and superior conchae are covered with specialized olfactory epithelium. Nasal Cavities External Dilated Vestibule: § Skin of the nose enters the nostrils, forming the external vestibule. § Contains sweat glands, sebaceous glands, and coarse, moist vibrissae (hairs). § Vibrissae filter particulate material from inspired air. Internal Nasal Cavity: § Within the vestibule, the epithelium transitions from keratinized to D non-keratinzed pseudostratified columnar epithelium, which also lines the nasal cavities. Respiratory Epithelium Pseudostratified columnar epithelium with cilia and goblet cells. Cell Types: § Ciliated cells. § Goblet cells: Filled with mucin glycoprotein granules. § Brush cells: Have sparse microvilli. Function as chemosensory receptors. § Small Granule Cells: Possess numerous dense core granules, part of the diffuse & Q. What would neuroendocrine system (DNES). brush happen if you inhale cells § Basal Cells: Mitotically active stem and t large amounts of progenitor cells. ciliated toxins, i.e., from cells Cells are in contact with a thick basement try to smoking/ industrial membrane u n push pollution? - back up + out Olfactory Epithelium G Covers the superior conchae at the roof of the nasal cavity. Cell Types: § Olfactory Neurons: Bipolar neurons distributed throughout the epithelium. num O Nuclei form an irregular row near the middle. Dendrite-end has knoblike swelling with basal bodies, which allow cilia to project into the aqueous layer. § These cilia have nonmotile axonemes and provide a large surface for transmembrane chemoreceptors. Respond to odoriferous substances by generating action potentials along axons that form the olfactory nerve. -mem - § Axons pass through the cribriform plate of the ethmoid C bone, synapse in the olfactory bulb. Olfactory Epithelium Supporting Cells: § Columnar cells with narrow bases and broad, cylindrical apexes with nuclei and microvilli. § Role not well understood, but they express abundant ion channels. Basal Cells: § Small, spherical, or cone-shaped cells near the basal lamina. § Stem cells for olfactory neurons and supporting cells. Pharynx Nasopharynx: § Respiratory epithelium. § Contains the medial pharyngeal tonsil (adenoids). § Houses the openings of the two auditory tubes from each middle ear cavity. Oropharynx: § Nonkeratinized stratified squamous epithelium. § Includes the palatine and lingual tonsils. Laryngopharynx: § Nonkeratinized stratified squamous epithelium. Larynx Rigid wall reinforced by hyaline cartilage (thyroid, cricoid, and inferior arytenoid cartilages) and smaller elastic cartilages (epiglottis, cuneiform, corniculate, and superior arytenoid cartilages). § Skeletal muscles control movements of cartilages for sound production. Epiglottis: § Flattened structure projecting from the proximal larynx. § Prevents swallowed food or fluid from entering the air passage. § Lingual surface has stratified squamous epithelium; laryngeal surface transitions to respiratory epithelium. Larynx Vestibule of Larynx: § Mucosa projects bilaterally into the lumen below the epiglottis. Upper pair: Immovable vestibular folds covered with respiratory epithelium, seromucous glands, and occasional lymphoid nodules. Lower pair: Vocal folds (cords) for phonation. Vocal Cords: § Covered with nonkeratinized stratified squamous epithelium. § Supported by the vocal ligament. § Vocalis muscle allows movement of vocal folds. Trachea Lined with respiratory mucosa. Lamina propria contains numerous seromucous glands producing watery mucus. The wall is reinforced by a series of about a dozen C-shaped rings of hyaline cartilage. § The cartilage rings keep the tracheal lumen open. § Trachealis between the open ends of the cartilage rings on the posterior surface. Bronchi In primary bronchi, cartilage rings encircle the lumen. § Bronchioles: loss of cartilage, gain of smooth muscle & MALT Small mucous and serous glands are abundant. Q. What kind of epithelium is present in A) large bronchus and B) tertiary bronchus? Bronchioles Lack both mucosal glands and cartilage. Larger bronchioles have ciliated pseudostratified columnar epithelium. § The epithelium decreases in height and complexity as bronchioles get smaller. § Smallest terminal bronchioles have ciliated simple columnar or simple cuboidal epithelium. The ciliated epithelial lining of bronchioles initiates the mucociliary apparatus or escalator. § Important in clearing debris and mucus. Terminal Bronchioles Terminal bronchioles are lined with cuboidal epithelium, consisting of club cells. 5 § Club cells are non-ciliated, dome-shaped apical ends containing secretory granules. - - Secrete surfactant lipoproteins and mucins. 3 Detoxify inhaled xenobiotic compounds via SER. Secrete antimicrobial peptides and cytokines. § Chemosensory brush cells and DNES small granule cells. § A small population of stem cells. § Elastic fibers and smooth muscle are present in the bronchiolar lamina propria. These components produce folds in the mucosa. Respiratory Bronchioles Each terminal bronchiole subdivides into two or more respiratory bronchioles. Respiratory bronchioles include saclike alveoli. Smooth muscle and elastic connective tissue comprise the lamina propria. The epithelium consists of club cells, with simple squamous cells at the alveolar openings and extending into the alveolus. Alveolar Ducts & Sacs Distal ends of respiratory bronchioles branch into alveolar ducts, which are lined by openings of alveoli. Both alveolar ducts and alveoli have extremely attenuated squamous cells. Lamina Propria of Alveolar Ducts: § A strand of smooth muscle cells surrounds each opening. § A network of elastic and collagen fibers supports both the duct and its alveoli. Lamina Propria of Alveolar Sacs: § Consists of a web of elastic and reticular fibers that encircle the alveolar openings and each alveolus. Alveoli Site of gas exchange: Exchange of O2 and CO2 with the blood in surrounding capillaries through alveolar walls. § Respiratory Membrane: Thin cells lining the alveolus (type I and type II pneumocytes) Fused basal laminae of these cells and the endothelial cells of capillaries. Thin capillary endothelial cells. Septa between neighboring alveoli consists of scattered fibroblasts and sparse ECM, particularly elastic and reticular fibers. § Elastic fibers allow alveoli to expand and contract. § Reticular fibers prevent collapse and excessive distention. § Interalveolar septa has the richest capillary networks in the body. Q. What are the implications of having such a large capillary bed? Alveoli Alveolar Cells Type I pneumocytes: § Type I epithelial cells have desmosomes and tight junctions. Type II pneumocytes: § Cuboidal cells. § Lamellar bodies contain lipids, phospholipids, and proteins, continuously synthesized and released at the apical cell surface. § Type II alveolar cells produce pulmonary surfactant - § Site of SARS-CoV-2 attachment! Dust Cells: § Phagocytose erythrocytes from damaged capillaries and particulate matter. Q. Remember heart failure cells from BMS200? Ventilation Boyle’s Law: The volume of an object and the pressure of gas it contains are inversely proportional when temperature remains constant. Inspiration: § Diaphragm flattens, increasing the volume of the thoracic cavity. § Contraction of the external intercostal muscles lifts the rib cage and pulls the sternum anteriorly. Raising a curved bucket handle away from the bucket. § Pressure within the thoracic cavity decreases. § The negative pressure generated creates a vacuum. § Air moves into the lungs. § Inspiration ends when thoracic volume ceases to increase. Ventilation Quiet Expiration: § Largely a passive process. § As inspiratory muscles relax, the diaphragm ascends, the rib cage descends, and elastic lung tissue recoils. Forced Expiration: § An active process. § Contraction of expiratory muscles (external and internal oblique, transverse and rectus abdominis). § Expiratory muscle contraction increases intra-abdominal pressure, forcing abdominal organs against the diaphragm and raising it. § These muscles also depress the rib cage. Ventilation  Accessory Muscles of Respiration Origin Insertion Innervation Active During: SCM Sternum of the Mastoid Process Accessory nerve Inspiration manubrium & medial clavicle Scalene Group TP of C3 – C7 Ribs 1 - 2 Anterior rami of Inspiration spinal nerves External Inferior border of Immediate rib below Intercostal Inspiration Intercostals ribs nerves Internal Costal groove of Immediate rib below Intercostal Expiration Intercostals ribs nerves Rectus Abdominis Pubic symphysis, Xiphoid process, Intercostal and Expiration pubic crest costal cartilages 5-7 subcostal nerves Diaphragm Xiphoid process, Central tendon of Phrenic nerve costal cartilages, diaphragm ribs, various ligaments References Lungs. In: Morton DA, Foreman K, Albertine KH. eds. The Big Picture: Gross Anatomy, Medical Course & Step 1 Review, 2nd Edition. McGraw Hill; 2018. Accessed August 13, 2023. https://accessmedicine- mhmedical- com.ccnm.idm.oclc.org/content.aspx?bookid=2478&sectionid=2020202 15 The Respiratory System. In: Mescher AL. eds. Junqueira's Basic Histology Text and Atlas, 16e. McGraw Hill; 2021. Accessed August 13, 2023. https://accessmedicine-mhmedical- com.ccnm.idm.oclc.org/content.aspx?bookid=3047&sectionid=2551221 31 § Nasal Cavities, Pharynx, Larynx, Trachea, Bronchial Tree, Lung