Lungs and Pleurae - PDF

The lungs and pleurae Learning objectives Learn about the anatomy of the lungs Learn about the Respiratory zone and its components Understand the lobes and bronchopulmonary segments Understand the innervation of the lungs Learn about the structure and function of the pleur...

The lungs and pleurae Learning objectives Learn about the anatomy of the lungs Learn about the Respiratory zone and its components Understand the lobes and bronchopulmonary segments Understand the innervation of the lungs Learn about the structure and function of the pleura as well as the surrounding tissues Learn about some pleural pathologies Lung Anatomy Conducting vs Respiratory zone Conducting Zone: Made up of the nose, pharynx, larynx , trachea, bronchi and bronchioles. Form a continuous passageway for air to move in and out of the lungs Respiratory zone: Deep inside the lungs Respiratory bronchioles, alveolar ducts and alveoli Conducting zone: Trachea Fibrocartilaginous tube Extends between the larynx and thorax Divides into the primary bronchi at the carina Blood supply : tracheal branches of inferior thyroid artery Innervation : pulmonary plexus Right main bronchus is much shorter than the left Conducting zone : bronchi and bronchioles The first bronchi branch from the trachea (right and left main bronchus) Branch further into the secondary bronchi (lobar bronchi) Then tertiary bronchi (segmental bronchi) Continue to branch until they reach the final and sixth generation of bronchi : the bronchioles Too small to be supported by cartilage  Respiratory Zones : Alveoli Where gas exchange occurs in the lungs Increase the surface area for gas exchange Single layer of alveolar epithelial cells : type 1 and 2 pneumocytes Type 1 pneumocytes cover 95% of entire surface of alveoli and are an excellent surface for gas exchange Type 2 pneumocytes produce surfactant. This helps to reduce the effects of surface tension. The balance of expansion and recoil determines the size of the alveoli Lung recoil is used to describe the tendency of the alveoli to rebound after inflation Special features of the alveoli Thin walls : decrease the distance for diffusion Close to the capillaries : decrease the distance for diffusion High in number : increased surface area for diffusion Collateral channels of ventilation: get past blockages Interconnected : help to pull each other open Lobes of the lung Horizontal fissure Obliquebut The right and left lung are similar fissure asymmetrical : Right lung has 3 lobes The right and left lung are similar Left Lung has 2 lobes but asymmetrical : Right lung has 3 lobes Left Lung has 2 lobes Oblique fissure  Bronchopulmonary segments The lobes further divide into segments associated with specific bronchi Surface mapping  Hilum (root) The point at which various structures enter and exit the lungs Surrounded by the pleura. Contains : Bronchi Pulmonary vasculature The phrenic nerve Lymphatics Bronchial vessels Pulmonary artery Pulmonary veins ( R and L) Mediastinum A central compartment in the thoracic cavity between the pleural sacs of the lungs. Divided into superior and inferior portions. Inferior then divides into middle and posterior portions. Pulmonary circulation The pulmonary circulation receives the entirety of the cardiac output from the right heart and is a low pressure, low resistance system. Can be divided into The arterial circuit The venous circuit The Lymphatics Bronchial circulation Innervation of the lungs The lung receives innervation from 2 main sources: The pulmonary plexus A combination of parasympathetic and sympathetic nerves Phrenic nerve Parasympathetic innervation causes constriction of the bronchi, dilation of pulmonary vessels and increase gland secretions Sympathetic innervation causes dilation of the bronchi and constriction of the pulmonary vessels Pulmonary Lymphatic system Maintains fluid homeostasis Fight infections However: A primary cancer may lead to cancer cells being transported around the body leading to metastasis The Pleura Parietal pleura Visceral pleura No anatomical connection between the right and left pleural cavities  Pleural Cavity The space between the visceral and parietal pleura. Pleural cavity filled with small amount of serous fluid with 2 key functions: Allows for reduced friction during respiration Generates surface tension Pleural recesses : Located posteriorly and anteriorly where the pleural cavity is not totally filled with lung parenchyma Costomedial recess : posterior to the sternum Costodiaphragmatic recess : between the diaphragmatic and costal pluera Surface tension Created by water molecules at Surfactant role in surface the air-liquid interface within tension: the alveoli - Secreted by the type 2 alveolar cells Pleural role in surface tension: - Reduces surface tension Promotes lung expansion - Increases lung compliance Prevents alveolar collapse - Prevents alveolar collapse Improves compliance - Facilitates alveolar recruitment Facilitates pressure changes Pleural Pathologies Pleural effusion Accumulation of fluid in the pleural space Common causes of Pleural effusion : Congestive heart failure Cancer Bacterial pneumonia Post surgery Pulmonary embolism Symptoms : Shortness of breath Chest pain Dry cough Imaging Empyema Collection of pus in the pleural cavity Common causes : Post surgery Pneumonia Alcohol abuse Trauma Symptoms : Pain Cough with increased sputum production Dullness in chest wall percussion Palpable fremitus Imaging Pneumothorax A collection of air outside the lung but within the pleural cavity. It occurs when air accumulates between the parietal and visceral pleura inside the chest. Causing the lung to collapse. Defined as tension or spontaneous. Pneumothorax TENSION : SPONTANEOUS: Trauma No cause / Atelectasis / Leak in the visceral pleura pathology Urgent decompression Treated with a drain required Mediastinum pulled TOWARDS Mediastinum pushed AWAY Increased plueral space pressure Tension VS Spontaneous Key points Lungs are made up of lobes: Pleura line the chest and the L 2 lobes outside of the lung R 3 lobes Reduce friction Generate surface tension Split into the conducting zone Pleural pathologies can prevent and the respiratory zone expansion of the lung or cause Alveoli are the site of gaseous collapse of the lung exchange Tension pneumothorax : moves Special features that help to away support diffusion of gas in and out of blood Spontaneous pneumothorax: Pulls towards  References Patwa, A. and Shah, A. (2015) ‘Anatomy and physiology of respiratory system relevant to anaesthesia’, Indian Journal of Anaesthesia, 59(9), p. 533. doi:10.4103/0019-5049.165849. Stump, B. et al. (2017) ‘Lymphatic changes in respiratory diseases: More than just remodeling of the lung?’, American Journal of Respiratory Cell and Molecular Biology, 57(3), pp. 272–279. doi:10.1165/rcmb.2016-0290tr. Anan, R.A. (2022) Empyema vs pleural effusion: Radiology reference article, Radiopaedia. Available at: https://radiopaedia.org/articles/empyema-vs-pleural-effusion-2 (Accessed: 17 November 2023). Garvia V, Paul M. Empyema. [Updated 2023 Aug 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459237/ Mahabadi N, Goizueta AA, Bordoni B. Anatomy, Thorax, Lung Pleura And Mediastinum. 2022 Oct 17. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan–. PMID: 30085590. Chaudhry R, Bordoni B. Anatomy, Thorax, Lungs. 2023 Jul 24. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan–. PMID: 29262068. Bustamante-Marin XM, Ostrowski LE. Cilia and Mucociliary Clearance. Cold Spring Harb Perspect Biol. 2017 Apr 3;9(4):a028241. doi: 10.1101/cshperspect.a028241. PMID: 27864314; PMCID: PMC5378048. McKnight CL, Burns B. Pneumothorax. [Updated 2023 Feb 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK441885/ Rad, A. (2023) Trachea, Kenhub. Available at: https://www.kenhub.com/en/library/anatomy/the-trachea (Accessed: 17 November 2023). Jany B, Welte T. Pleural Effusion in Adults-Etiology, Diagnosis, and Treatment. Dtsch Arztebl Int. 2019 May 24;116(21):377-386. doi: 10.3238/arztebl.2019.0377. PMID: 31315808; PMCID: PMC6647819.