Lecture_Microscopic structure of the lungs_AR.pdf

Lecture Medicine Duration ~45 Mins Microscopic structure of the lungs Dr. Arman Rahman, MD, MPH, Ph.D. ANAT20070 Learning Outcomes ❖ Identify and describe the primary structures in the organisation of the respiratory system ❖ Identify the main histological aspects of each component of the conducting...

Lecture Medicine Duration ~45 Mins Microscopic structure of the lungs Dr. Arman Rahman, MD, MPH, Ph.D. ANAT20070 Learning Outcomes ❖ Identify and describe the primary structures in the organisation of the respiratory system ❖ Identify the main histological aspects of each component of the conducting system and gas exchange region ❖ To relate structure to function of the conducting airways and gas exchange region photograph by Martin Dohrn/Royal College Of Surgeons/ The structure of the respiratory system closely relates to its function Structure is the arrangement of inter-related elements: e.g. the building blocks such as tissue types: Epithelium- number of cell layers, lines body surfaces, Connective tissue- collagen and elastin Muscle- smooth muscle and skeletal muscle Nervous- receive stimuli from internal and external environments, integrates signals Function is the operation of each individual component as part of the structure Functions of the Respiratory system Airflow: movement of air in and out of site of gaseous exchange Gas exchange and transport of oxygen and carbon dioxide: -Provide oxygen: air →lungs → blood→ tissues -Eliminate carbon dioxide : tissues → blood→ lungs →air Conditions air: warm, filter and humidify air Acid-base regulation: by controlling carbon dioxide, regulate blood pH Temperature regulation Functions of the Respiratory system Metabolism: removal of noradrenaline, prostaglandins, 5-HT Hormonal activity: angiotensin II is formed from angiotensin I in the lungs Immune protection: defend against microbes, toxic chemicals and foreign matter Maintain airway patency Production of sound/speech Olfactory sensation Organisation of the Respiratory System ▪ Inspiration is the movement of air from the external environment into the alveoli ▪ Expiration is the movement of air from the alveoli to the external environment ©McGraw-Hill, Vander’s Human Physiology 15th Edition, Fig. 13.1 General Histology of the Respiratory Tract Epithelium: Respiratory System is covered by epithelium which varies down the tract Initially epithelial cells are pseudostratified columnar ciliated, then cuboidal then squamous Glands and goblet cells: Upper respiratory tract has abundant glands, but they are absent from bronchioles onwards. Abundant goblet cells decrease in number until the bronchioles. Cartilage: Cartilage is found throughout the respiratory tract until the small bronchi. In trachea cartilage is found in C-shaped rings; in bronchi as plates. Smooth muscle Smooth muscle in the trachea joins the C-shaped cartilage. Smooth muscle is found throughout the bronchi and bronchioles which it surrounds completely. Elastic tissue: Elastic tissue is found in the bronchi and bronchioles. Conducting Zone: (Dead space region) Nasal cavity → terminal bronchioles -Get air in -Warm moisten air -Clean air Respiratory Zone: Respiratory bronchioles → alveoli -Gas exchange mechanism Upper Respiratory Tract Koyoma et al 2021, International Journal of Molecular Sciences 22(16):8912 Nose and Nasal Cavity Air enters the nasal cavity via the nostrils (nares) Nose is subdivided into two nasal cavities (NC) separated by the nasal septum (NS) Vestibule lined with hairs to trap large particles and mucus to trap debris in air John Bavosi/Science Photo Library Nasal cavities and paranasal sinuses (PS) are line by respiratory mucosa principally involved in filtering, humidifying and adjusting temperature of inspired air Turbinate bones (TB) project into the nasal cavity and increase the surface area which air flows over Wheater’s Functional Histology, 6th Edition, Elsevier Fig. 12.2 Nasal Mucosa Mucosa of the nasal cavity is lined with pseudostratified ciliated columnar respiratory epithelium (RE) Contains mucin-secreting goblet cells Supported by lamina propria rich in blood vessels (V) and serous (S) and Mucous (M) glands, the secretions of which trap small particles Mucous layer propelled to the pharynx by cilia (muco-ciliary escalator) for digestion Wheater’s Functional Histology, 6th Edition, Elsevier Fig. 12.3 Pharynx Passageway that connects the nasal and oral cavity Shared by the digestive and respiratory systems Divided into three sections by location: Nasopharynx – superior portion above the soft palate Oropharynx – back of the mouth cavity down to the epiglottis Hypopharynx – between the hyoid bone and the esophagus Pharynx Nasopharynx- respiratory epithelium and lamina propria contains seromucous glands Lymphoid tissue (L) (Waldeyer ring of lymphoid tissue) adenoid Wheater’s Functional Histology, 6th Edition, Elsevier Fig. 12.4 Oropharynx non-keratinised stratified squamous epithelium Dr. P. Marazzi/Science Photo Library Larynx Larynx is continuous with the trachea Superior end is attached to the hyoid bone that lies below the epiglottis Consists of 9 laryngeal cartilages (hyaline and elastic) connected by muscle and ligaments Stojanovic, S. 2013: Innovative Rheumatology, DOI: 10.5772/51730 Maintains open passageway for air movement Prevents swallowed materials from entering the trachea Sound production Note the change from stratified squamous to pseudostratified, ciliated (or respiratory epithelium). Lower Respiratory Tract ©McGraw-Hill, Vander’s Human Physiology 15th Edition, Fig. 13.1 Airway Branching Dichotomous airways Large surface area at the level of the alveoli Large area for gas exchange ©McGraw-Hill, Vander’s Human Physiology 15th Edition, Fig. 13.2 Costanzo, 4th edition Trachea Extends from larynx to midline of thorax where it divides into the right and left main bronchi (~10cm long) Function: warm, clean and conduct air Distinct layers Mucosa (M) Respiratory epithelium -Pseudostratified ciliated tall columnar cells -Goblet cells -Serous Cells -Basal cells (lie close to basement membrane) -Brush Cells Basement membrane Lamina Propria -Highly vascular connective tissue and elastic fibres Trachea Submucosa (SM) Mixed seromucous glands C-shaped hyaline cartilage rings (C) ~16-20 pieces to provide flexible support to the airway Bands of smooth muscle (trachealis muscle) join the free ends of the posterior rings (T) contraction reduces the diameter e.g. during coughing Adventitia: Connective tissue which tracheal adjacent structures Wheater’s Functional Histology, 6th Edition, Elsevier Fig. 12.7 Wheater’s Functional Histology, 6th Edition, Elsevier Fig. 12.6 Wheater’s Functional Histology, 6th Edition, Elsevier Fig. 12.9 Primary Bronchus Cilia (CC) ‘Mucociliary escalator’ - carry particles toward the pharynx, to be swallowed Right primary bronchus is shorter, wider and more vertical Basic structure is similar to the trachea however: Respiratory epithelium is less tall with fewer goblet cells (GC) The lamina propria (LP) has more elastin fibres (El) and is separated from the submucosa (SM) with smooth muscle (M) which becomes more prominent in distal bronchi Submucosa has less seromucinous glands Cartlidge is in flattened interconnected plates rather than distinct rings Wheater’s Functional Histology, 6th Edition, Elsevier Fig. 12.8 Airway Branching ©McGraw-Hill, Vander’s Human Physiology 15th Edition, Fig. 13.2 Bronchioles Airway