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 pleura...

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 The right and left lungOblique fissu are similar but asymmetrical : re Right lung has 3 lobes The right and left lung are Left Lung has 2 lobes similar but asymmetrical : Right lung has 3 lobes Left Lung has 2 lobes Oblique fissu re  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 Surfactant role in surface molecules at the air-liquid tension: interface within the alveoli - Secreted by the type 2 alveolar cells Pleural role in surface - Reduces surface tension tension: - Increases lung Promotes lung expansion compliance Prevents alveolar collapse - Prevents alveolar collapse Improves compliance - Facilitates alveolar Facilitates pressure recruitment 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 Pneumothora x 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 pathology pleura Treated with a drain Urgent decompression Mediastinum pulled required 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 Reduce friction R 3 lobes Generate surface tension Split into the conducting Pleural pathologies can zone and the respiratory prevent expansion of the zone lung or cause collapse of the Alveoli are the site of lung gaseous exchange Tension pneumothorax : Special features that help to moves away support diffusion of gas in Spontaneous pneumothorax: and out of blood Pulls towards  References Patwa, A. and Shah, A. 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