General Histology Lecture 5 PDF

General Histology Lecture 5 Respiratory System 1 Ahmed Abdul-Aziz Muhamed. PhD Reference : Anthony L. MESCHER, Jonquiere's Basic Histology TEXT & ATLAS  Respiratory System functional Components 1. Conducting portion 2. Respiratory portion...

General Histology Lecture 5 Respiratory System 1 Ahmed Abdul-Aziz Muhamed. PhD Reference : Anthony L. MESCHER, Jonquiere's Basic Histology TEXT & ATLAS  Respiratory System functional Components 1. Conducting portion 2. Respiratory portion Nasal cavity Respiratory bronchioles Larynx Alveoli Trachea Bronchi Gas exchange Bronchioles 3. Pleura Conduct air to and from alveoli Condition the air (warm, humidify, filter) 2  Respiratory system Function 1. Gas exchange and acid-base balance 2. Olfaction 3. Phonation 4. Haematopoiesis: platelet biogenesis and reservoir for haematopoietic progenitors (Lefrançais et al., 2017; Borges et al., 2017) 5. Pulmonary defense 6. Compression abdominal cavity 7. Pulmonary metabolism and handling of bioactive materials 3 Anatomy of the respiratory system Embryology of the respiratory system Stuff that develops from the foregut Development of respiratory diverticulum (bud) Endoderm gives rise to the epithelium and glands of the larynx, trachea, bronchi and the pulmonary epithelium. Mesoderm gives rise to the connective tissue, cartilage and smooth muscle of the respiratory tract.  Development of bronchi and bronchioles The lung bud divides into two bronchial buds, which divide and form secondary and tertiary bronchi. As bronchi develop, the surrounding mesenchyme forms cartilage, smooth muscle, connective tissue and capillaries.  Walls of the Conducting System The walls of the conducting system change in thickness and composition from region to region. Components include: – Epithelium (“respiratory epithelium”) – Lamina propria – Mucous and serous glands – Cartilage – Smooth muscle – Adventitia  Respiratory Epithelium Cell Types Ciliated columnar cells: most abundant cell type. Cilia beat in unison and move mucus and trapped particles to oropharynx, where it is swallowed or expectorated. Goblet cells: produce mucus. Basal cells: stem cells that replenish epithelium. Hard to see. Brush cells: Columnar cells. No cilia but have apical microvilli. Hard to see. Neuroendocrine cells: epithelial cells containing hormones. Hard to see. Respiratory epithelium  1. Nasal Cavity Respiratory epithelium everywhere except at the top (which has specialized olfactory epithelium). Serous and mucous glands and numerous blood vessels in lamina propria. Nasal septum: midline structure consisting of bone and hyaline cartilage. Nasal fossa: chambers on each side of septum.  Three types of epithelium were found in nasal cavity 1. Nasal vestibule (Stratified squamous epithelium) 2. Nasal cavity proper (Respiratory epithelium) 3. Olfactory area (Olfactory epithelium) Stratified squamous epithelium  1. Larynx and epiglottis Epiglottis covers laryngeal opening during swallowing. Core of elastic cartilage. Superior surface: nonkeratinized stratified squamous epithelium. Inferior surface: respiratory epithelium Vocal folds are covered by nonkeratinized stratified squamous epithelium Laryngeal cartilages support the wall of the larynx and serve as attachments for vocalis muscles. False vocal folds are covered by respiratory epithelium Epiglottis: elastic cartilage  Trachea Extends from larynx and divides into two primary bronchi. Contains 16-20 C-shaped hyaline cartilage rings with the dorsal opening bridged by smooth muscle (trachealis muscle). Lined by respiratory epithelium. Seromucous glands in lamina propria and sub- mucosa. Composes of 4 layers 1. Mucosa 2. Sub-mucosa 3. Cartilage framework 4. adventitia Trachea divides into 2 primary bronchi. Trachea  Trachea histology Trachea: respiratory epithelium Trachea: hyaline cartilage  Bronchi Trachea divides into two primary bronchi, which divide into secondary bronchi. Secondary bronchi divide into tertiary bronchi, which supply bronchopulmonary segments. Tertiary bronchi divide into smaller bronchi, which divide into bronchioles. Bronchi undergo 9-12 branching's. As branching progresses: Connective tissue decreases in thickness Relative amount of smooth muscle and elastic tissue increases Cartilage disappears (gone by bronchioles)  Wall of Bronchus Respiratory epithelium (E) Lamina propria (LP) Smooth muscle (SM) Hyaline cartilage (C) Nerves (N) and blood vessels (V) Note the order of structures: E → LP → SM → C  Bronchioles NO glands or cartilage. Larger bronchioles have respiratory epithelium. Smaller bronchioles have low columnar epithelium. In asthma, the smooth muscle in the bronchioles constricts, causing difficulty breathing.  Terminal Bronchioles Simple cuboidal epithelium with cilia. Also: Clara cells (non-ciliated epithelial cells with secretory granules). No goblet cells. As you go down the respiratory tract, goblet cells Make surfactant components, are lost before cilia. break down mucus, detoxify harmful substances, transfer IgA, fight bacteria  When can the baby breathe? By week 24, respiratory bronchioles are present and lungs are vascularized. Respiration is possible but chances of survival outside placenta are slim. Weeks 24-26: terminal alveolar sacs develop and type II pneumocytes secrete surfactant (decreases surface tension) By week 26-28: there are enough alveolar sacs and surfactant to allow a prematurely born infant to survive without medical intervention.  Strange but true… 95% of mature alveoli develop after birth! The newborn infant has only 1/6 – 1/8 the number of alveoli as adults. Most alveolar growth is done by age 8. At birth, the lungs are half-filled with amniotic fluid. This fluid is cleared through the mouth and nose by pressure on thorax during delivery. It also is reabsorbed into pulmonary blood vessels and lymphatics.