Trachea, Bronchial Tree, and Lungs Lecture Slides (MD3001 2023) PDF

Trachea, bronchial tree and lungs MD3001 September 2023 Dr. Alex Gardner [email protected] Learning outcomes By the end of this lecture, time spent in the dissecting room, and further private study you should be able to: 1. Recall the structures that form the conducting and respiratory porti...

Trachea, bronchial tree and lungs MD3001 September 2023 Dr. Alex Gardner [email protected] Learning outcomes By the end of this lecture, time spent in the dissecting room, and further private study you should be able to: 1. Recall the structures that form the conducting and respiratory portions of the respiratory tract 2. Describe the structure and function of the trachea 3. State the relations of the trachea 4. Describe how the epithelium and structure of the bronchial trees change as they branch into the lungs 5. Describe the structure and relations of each lung 6. Describe the relationships of the structures that make up the root of the lung 7. Describe the neurovascular (inc. lymph drainage) supply of the lungs 8. Explain the concept of, and clinical significance of the bronchopulmonary segments 9. Discuss the clinical conditions that may affect the respiratory tract MD3001 2023 2 Sources N.B. Consult chapters on thorax, head and neck MD3001 2023 3 Respiratory system - reminder Conducting portion: • Nose, nasal cavity, paranasal sinuses ✔ • Pharynx (nasopharynx, oropharynx, laryngopharynx) ✔ • Larynx ✔ • Trachea • Bronchi, bronchial tree • Terminal bronchioles Respiratory portion (gas exchange): • Respiratory bronchioles • Alveoli (ducts and sacs) • 400 million per lung! • Large surface area • Rich vascular supply MD3001 2023 4 Trachea - overview • Fibrous and cartilaginous tube conducting air from larynx to bronchi • 10-11 cm long • ~2.5cm diameter, from C6 to T4/5 vertebral levels • Has “c-shaped” cartilage rings to maintain patency • Posteriorly, smooth muscle called trachealis which joins each end of the rings, controls diameter MD3001 2023 5 Trachea - overview • Continues airway from the larynx (cricotracheal membrane connect first tracheal cartilage with cricoid cartilage) • Divides into two main (primary) bronchi forming the carina (T4/5) • Trachea begins in the neck, then enters the superior mediastinum via the thoracic inlet MD3001 2023 6 Trachea – surrounding structures Posterior • oesophagus Anterior • Thyroid gland isthmus • • • 1st Cartilage ring is palpable Thyroid gland obscures cartilages 2-4 Palpable superior to jugular notch • Brachiocephalic trunk, L brachiocephalic vein • Cardiac plexus nerves (sympathetic and parasympathetic) • Tracheobronchial nodes • Manubrium (manubriosternal joint also marks bifurcation of trachea) MD3001 2023 7 Trachea – surrounding structures Lateral • Thyroid gland lobes • Parathyroid glands • Common carotid arteries • Aortic arch, common carotid and subclavian artery (L) • Azygous arch, Vagus nerve (R) Posterolateral • Recurrent laryngeal nerves MD3001 2023 8 Trachea – surrounding structures MD3001 2023 9 Trachea – neurovascular supply • Supplied by inferior thyroid artery and bronchial arteries • Drains to inferior thyroid and bronchial veins • Lymph drains to pre and para tracheal nodes MD3001 2023 10 Trachea – neurovascular supply • Supplied by the pulmonary plexus – Sympathetic from sympathetic trunk (dilation) – Parasympathetic from vagus nerve (constriction) MD3001 2023 11 Bronchi • Continuation of trachea, have smooth muscle and complete cartilage rings • Right and left main/primary bronchi • Secondary (lobar) bronchi (3 right, 2 left) • Tertiary (segmental) bronchi • Bronchial tree • Note: bronchi receive blood from bronchial arteries, one right, two left. MD3001 2023 12 Bronchioles • Serial divisions of conducting bronchioles, down to 20-25 generations • As number increases size individually decreases but total surface area increases • Then becomes respiratory bronchioles -> alveolar ducts -> alveolar sacs MD3001 2023 13 Alveoli • Pulmonary vasculature branches in a similar fashion to bronchi • Forms capillary beds around alveoli • Alveoli are a single cell thick • This provides a large surface area for efficient gas exchange MD2001 2023 14 Histology of respiratory tree - trachea • Cartilage ossifies due to age • Respiratory epithelium – ciliated pseudostratified columnar epithelium • Note trachealis muscle (TM) Oesophagus, not to scale MD2001 2023 15 Histology of respiratory tree - bronchi ? ? ? ? MD2001 2023 ? 16 Histology of respiratory tree - bronchiole Note: • Smooth muscle but no cartilage, no glands • Vascular supply (BV) adjacent • Still respiratory epithelium • Surrounding alveoli MD2001 2023 17 Histology of respiratory tree – terminal bronchiole Note: • Lumen on right • Alternating thick and thin portions • sparse smooth muscle • CC = club cells (formerly clara cells) • Club cells are non-ciliated, cuboidal epithelium • Club cells produce protective secretions MD2001 2023 Lumen, not to scale 18 Histology of respiratory tree – Acini Note: • Capillaries • Type I pneumocytes • Type II pneumocytes (SC = septal cell, produce surfactant) • Alveoli = A MD2001 2023 19 Histology of respiratory tree Note: • The above structures contain abundant elastic protein fibres (elastin), although it doesn’t show very well on H&E sections MD2001 2023 20 Lungs Functions: • Primarily gas exchange • pH balance • Other metabolic functions – angiotensin 1 to angiotensin 2 • Prostaglandin synthesis MD3001 2023 21 Lungs • Right and left • Lobes are visibly defined, separated by fissures • Occupy the lateral parts of the thoracic cavity • Costal, mediastinal, diaphragmatic surfaces • Connection via hilum • Root of lung = vasculature and airways entering the lung • Covered in visceral pleurae MD2001 2023 22 Lung segments Right and Left: • Superior lobe • Apical • Posterior • Anterior • Inferior lobe • Superior (apical) • Anterior basal • Posterior Basal • Medial basal • Lateral basal Right only: Lateral and medial segments of middle lobe Left only: Superior lingular and inferior lingular of superior lobe MD2001 2023 23 Lung segments • Supplied by tertiary (segmental) bronchi • 10 per side • Pyramidal shape with apices converging towards to hilum • Separated by septa • Infection typically confined to a segment • Can be resected as one unit e.g. in cancer • Own arterial supply from pulmonary artery • Veins and lymphatics can cross septa MD2001 2023 24 Left lung and mediastinum MD2001 2023 25 Right lung and mediastinum MD2001 2023 26 Root of lung Connection of lung to the mediastinum Covered by a pleural sleeve which also extends inferiorly as pulmonary ligament Contains: • Main bronchus • Pulmonary artery (deoxygenated blood to lung) • Pulmonary veins (oxygenated blood to heart) • Bronchial arteries – supplying bronchi and structural tissue of lung • Bronchial veins • Lymph nodes and vessels MD3001 2022 27 Lung arterial supply Bronchial arteries • Supply tissue of respiratory system • Two left, from aorta • One right, from 3rd intercostal artery Pulmonary arteries • Deoxygenated blood from heart • Via pulmonary trunk, then right and left pulmonary arteries • Most superior hilum structure • Large diameter, low pressure MD3001 2023 28 Lung arterial supply Bronchial arteries • Supply tissue of respiratory system • Two left, from aorta • One right, from 3rd intercostal artery Pulmonary arteries • Deoxygenated blood from heart • Via pulmonary trunk, then right and left pulmonary arteries • Large diameter, low pressure • Anterior to bronchi, just below tracheal bifurcation • Left shorter than right MD3001 2023 29 Lung venous drainage Bronchial veins • Drain to azygous (R) or hemiazygos vein (L) • Or enter the pulmonary circulation and return to heart Pulmonary veins • Carrying oxygenated blood toward heart • Two per side (superior and inferior) MD3001 2023 30 Lung innervation – pulmonary plexus • Anterior and larger posterior parts, relative to trachea and bronchi • From Vagus (parasympathetic) and sympathetic trunk (sympathetic) • Branches from plexus distributed along vessels and airway branches • Also supplies visceral pleura • Parasympathetic -> bronchoconstriction, vasodilation, secretomotor • Sympathetic -> bronchodilation, vasoconstriction, MD3001 2023 31 Lung lymphatics Subpleural plexus Intrapulmonary nodes Hilar nodes Tracheobronchial nodes (Sup. + Inf.) Paratracheal nodes Bronchomediastinal trunks Note: Inferior/carinal nodes drain lower lobes of both lungs, primarily draining to the right side MD3001 2023 32 Lungs – clinical considerations Asthma COPD Cancer Foreign body aspiration Pneumothorax/haemothorax Pleurisy Cystic fibrosis Bronchoscopy Tracheostomy Pulmonary embolism MD3001 2023 33 Lungs – clinical considerations Asthma • Commonest lung condition • >8 million in UK • Inflammation of airways = reduced diameter • Allergic/nonallergic/occupational • Management involves a hierarchy of pharmacological treatment • Salbutamol -> β2 adrenoreceptor agonist = relaxes bronchial smooth muscle MD2001 2023 34 Lungs – clinical considerations COPD • Chronic obstructive pulmonary disease • Common • Biggest risk factor is smoking • Mucus hypersecretion and alveolar destruction • Emphysema or chronic bronchitis MD2001 2023 35 Lungs – clinical considerations Cancer • Bronchial carcinoma (95% of primary tumours) • Smoking is biggest risk factor • Often very poor prognosis • Also, common site for metastatic tumour • Metastases often via lymphatic spread • Mesothelioma = affecting pleura – asbestos • Tumour in apical lobe (5%) = Pancoast tumour, can cause nerve compression – Sympathetic trunk, above T4 = Horner’s syndrome (oculosympathetic paresis) – Brachial plexus = pain in shoulder/scapula/arm, paralysis of hand MD3001 2023 36 Lungs – clinical considerations Pneumothorax • Air in pleural cavity • “collapsed lung” • Spontaneous (Tall, thin, male) • Higher risk in certain syndromes • Penetrating chest injury or damage to lung https://www.radiologymasterclass.co.uk/tutorials/chest/chest_tubes/chest_xray_chest_drain MD2001 2023 37 Lungs – clinical considerations Pneumonia • Infective – bacterial, viral, fungal • Affect lobe/segment “lobar pneumonia” or multiple • Often affects those with underlying health conditions or frailty • Lying supine is a risk factor From: https://www.mdpi.com/2075-4418/13/6/1107 MD2001 2023 38 Lungs – clinical considerations Cystic fibrosis • Commonest genetically transmitted disease • Autosomal recessive 1 in 2000 • Mucous is too thick due to abnormal ionic composition (malfunctioning chloride transporter) MD3001 2023 39 Lungs – clinical considerations Foreign body aspiration • Items have a tendency to the right main bronchus (wider, shorter, more vertical) • N.B. not all items will be detectable by x-ray • Bronchoscopy to visualise/retrieve MD2001 2023 40 Lungs – clinical considerations Pulmonary embolism • Blockage occurs in pulmonary artery • Typically clot (thrombus) from lower limb • Can be fat, air, tumour • Risk factors = immobilisation, recent surgery, malignancy, paralysis, smoking, obesity MD3001 2023 From: https://radiopaedia.org/articles/pulmonary-embolism-summary?lang=gb 41 Lungs – clinical considerations Tracheostomy • Not an emergency procedure • More likely to be longer term • N.b. inferior thyroid veins MD3001 2023 42 Lungs – clinical considerations Bronchoscopy • Scope to visually examine the lungs • Done under sedation • May also have device to remove foreign body or take a biopsy MD3001 2023 https://bmcsurg.biomedcentral.com/articles/10.1186/s12893-020-00825-5 43 EMQ style Q • Lung tissue contains certain proteins that enable function. What key protein enable the recoil of lungs? • Collagen type 1 • Collagen type 2 • Elastin • Actin • Myosin 44 SAQ style Q • Describe the non-lymphatic structures found at the hilum of the lungs and their function. (4 marks) • • • • Main bronchus – conducts air Pulmonary artery – conducts deoxygenated blood from heart to lungs Pulmonary veins - conducts oxygenated blood from lungs to heart Bronchial artery/ies – supplies lung tissue with oxygenated blood 45