Respiratory System Lecture Notes PDF

General Histology– Year 2 Lecture: Respiratory system Part 2 By Lecturer: Dr. Hanaa Ali Hussein...

General Histology– Year 2 Lecture: Respiratory system Part 2 By Lecturer: Dr. Hanaa Ali Hussein Department: Basic Sciences College of Dentistry University of Basrah University of Basrah – College of Dentistry– Basic Sciences  Bronchi The walls of Bronchi is composed of : 1. Mucosa: have Respiratory epithelium. 2. Muscle coat: two distinct layers of smooth muscle fibers arranged in opposite direction. 3. Submucosa: contains Seromusous gland and Lymphoid elements. 4. Cartilage: contains Irregular plate of hyaline cartilage and solitary lymphoid nodules. Bronchi have "plates" of cartilage 5. Adventitia: the deepest layer separating the bronchus from surrounding tissues University of Basrah – College of Dentistry– Basic Sciences 2 University of Basrah – College of Dentistry– Basic Sciences 3  Bronchioles The bronchi branch into smaller tubes called bronchioles which end in the pulmonary alveolus. It is divided into three types: 1. Preterminal (1 ry) Bronchioles 2. Terminal (2 ry) Bronchioles 3. Respiratory (3 ry) Bronchioles University of Basrah – College of Dentistry– Basic Sciences 4 1. Preterminal (1 ry) Bronchioles 1. Mucosa: has longitudinal fold: a. Epithelium: Simple columnar ciliated epithelium with occasional goblet cells. b. Lamina propria: C.T rich in elastic fibers. 2. Smooth muscle: 2 helically arranged smooth muscle layers. 3. Adventitia C.T: No cartilage, No seromucous, no lymph nodules. University of Basrah – College of Dentistry– Basic Sciences 5  2. Terminal bronchioles  Similar structure to preterminal bronchioles, but they are lined by simple columnar or simple cuboidal cells partially ciliated epithelium with Clara cells (no goblet cells)  Less than 0.5 mm in diameter  Clara cells, secretory cell, dome-shaped, secret surfactants that decrease the surface tension of fluid that moistens and protects the surface of the bronchial lining. University of Basrah – College of Dentistry– Basic Sciences 6  3- Respiratory bronchioles  Each terminal bronchiole gives two or three respiratory bronchioles. These are lined by simple ciliated cuboidal cells, with a small number of non ciliated Clara cells.  Lamina propria is rich in smooth muscle fibers and elastic fibers.  The wall of respiratory bronchioles is interrupted by the alveolar sacs and alveolar ducts, where the tissue changes into simple squamous epithelium. University of Basrah – College of Dentistry– Basic Sciences 7  Histology of the Alveolar Region Alveolar duct Has thin discontinuous lined by simple squamous epithelium. Lamina propria has smooth muscles which disappear distally, and replaced by elastic and reticular fibers. Alveolar sacs: Are formed the opening of several alveoli, attached to the ducts. The wall of alveolar ducts consist almost of pulmonary alveoli Alveoli  Alveoli are separated by Interalveolar septum lying between thin epithelial lining of two neighboring alveoli. Alveoli are specialized for O2 and CO2 exchange between air and blood  Interalveolar septum contains a network of capillaries supported by reticular and elastic fibers, sometimes fibroblasts, macrophages and mast cells. University of Basrah – College of Dentistry– Basic Sciences 8 University of Basrah – College of Dentistry– Basic Sciences 9  Elastic fibers- enable the alveoli to expand during inspiration and passively contract during expiration.  Reticular fibers support and prevent over distention of the alveoli.  Septum contains pores (ALVEOLAR PORES OF KOHN) help in passage of air from one alveolus to another, thus equalizing Pressure in the alveoli. University of Basrah – College of Dentistry– Basic Sciences 10 Alveolar epithelial cells are: 1. Type I Pneumocytes 2. Type II Pneumocytes 3. Macrophages or Dust cells 1. Alveolar Type I cells  Line 95% of the alveolar surfaces  Simple squamous epithelium  Function: Exchange of gases 2. Alveolar Type II cells  Line 5% of the alveolar surfaces  Cuboidal or rounded cells with foamy cytoplasm and central nucleus:  Function: 1- Synthesis & secretion of pulmonary surfactant. 2- Renewal of alveolar epithelial cells. University of Basrah – College of Dentistry– Basic Sciences 11 3. Alveolar macrophages-dust cells  Usually free in the alveolar lumen, also in tissues between alveoli.  Derived from Monocytes and are part mononuclear phagocytic system.  Main function is to clean the alveoli of invading microorganisms and inhaled particulate matter by phagocytosis. University of Basrah – College of Dentistry– Basic Sciences 12  Lung pleura  The pleura are thin membranes that line the lungs and the inside of the chest cavity and act to lubricate and facilitate breathing.  Is formed of two layers:  The outer layer is called the parietal pleura and attaches to the chest wall. The inner layer is called the visceral pleura (serous membrane) and covers the lungs, blood vessels, nerves, and bronchi.  Parietal pleura is formed of simple squamous mesothelium and loose C.T that extends into the lung tissue  Normally, a small amount of fluid is present in the pleura. University of Basrah – College of Dentistry– Basic Sciences 13 University of Basrah – College of Dentistry– Basic Sciences 14