Histology of Respiratory and Digestive Systems PDF

# Respiratory System ## Pharynx * The pharynx is a tubular structure extending from the base of the skull to the sixth cervical vertebra. * It is divided into nasopharynx, oropharynx, and laryngopharynx, each lined with different types of epithelium. * The nasopharynx contains pharyngeal tonsils a...

# Respiratory System ## Pharynx * The pharynx is a tubular structure extending from the base of the skull to the sixth cervical vertebra. * It is divided into nasopharynx, oropharynx, and laryngopharynx, each lined with different types of epithelium. * The nasopharynx contains pharyngeal tonsils and the opening of the auditory tube. * The oropharynx houses the palatine tonsil. * The laryngopharynx is a continuation of the pharynx into the esophagus. ## Larynx * The larynx is responsible for voice production and is situated above the trachea. * It has a cartilaginous framework composed of various cartilages. * The lining epithelium varies depending on the location within the larynx. * Vocal cords are present within the larynx, involved in sound production. ## Trachea * The trachea, or windpipe, is a flexible cartilaginous tube extending from the lower border of the cricoid cartilage to the level of T4. * It is supported by C-shaped hyaline cartilage rings. * The trachea’s wall consists of mucosa, submucosa, cartilage, and adventitia layers. * Goblet cells and cilia are found in the epithelium of the trachea. ## Intrapulmonary Bronchus, Bronchiole, and Alveoli * The bronchial tree within the lungs consists of intrapulmonary bronchi, bronchioles, respiratory bronchioles, alveolar ducts, and alveoli. * As the bronchial tree branches further into the lungs, the structure of the airways changes. * Smaller bronchioles are characterized by the presence of Clara cells, which secrete a glycoprotein to protect against pollutants. * Respiratory bronchioles transition from conducting to respiratory airways, featuring alveolar outpouchings. * Alveoli are the primary sites of gas exchange and are lined by type I and type II pneumocytes. * Type II pneumocytes produce pulmonary surfactant, reducing surface tension in the alveoli and preventing their collapse during expiration. ## Diagram of the Trachea The diagram shows a cross-section of the trachea. * On the left is a microscopic view of the trachea at 300x magnification. The image highlights the mucosa, seromucosus gland and hyaline cartilage. * On the right is a labelled schematic diagram of the trachea, showing the lumen of the trachea. * Arrows show the position of: * Posterior * Anterior * Esophagus * Trachealis Muscle * Adventitia * Submucosa ## Diagram of Bronchial Tree and Intrapulmonary Bronchus The diagram shows: * On the left is a schematic diagram of a bronchial tree, showing the position of: * Principal bronchus * Secondary bronchi * Tertiary bronchus * Bronchiole * Respiratory bronchiole * Alveolar duct * Alveoli * On the right is a microscopic view of the cross-section of an intrapulmonary bronchus. The image highlights the pseudostratified ciliated columnar epithelium, lamina propria, smooth muscle, submucosa, serous gland, hyaline cartilage and adventitia. ## Respiratory Diseases * **Premature newborns are at risk of developing respiratory distress syndrome (RDS) due to their underdeveloped lungs and the absence of surfactant,** which prevents alveoli from collapsing. This condition leads to difficulty in breathing and is characterized by the presence of a hyaline membrane in the airways. Glucocorticoids can induce surfactant production in these cases. * **Asthma is a chronic condition characterized by bronchospasms and mucosal inflammation in response to allergens or irritants.** It results in narrowed airways and can be treated with bronchodilators like epinephrine and anti-inflammatory medications. * **Exposure to irritants, such as cigarette smoke, can lead to squamous metaplasia,** a transformation of the respiratory epithelium from ciliated columnar to stratified squamous. This change is an early step in the development of squamous cell carcinoma, a type of lung cancer. * **Emphysema is a chronic obstructive pulmonary disease (COPD) associated with lung damage caused by cigarette smoking.** It leads to the destruction of alveoli and reduced lung elasticity, resulting in difficulty exhaling air and shortness of breath. # Digestive System ## Features of the Digestive System * **Oral cavity, digestive tract digestive glands** * **Main function: ingest food and to digest the food as it passes along the tract** * **Organs of the digestive tract are all hollow** * **Composed of four general tunic layers:** * **Innervated by the enteric portion of the autonomic nervous system** * **Include epithelium, connective tissue, muscle, blood and lymphatic vessels, lymphatic nodules, and nerve fibers** * **contain glands in the lamina propria or submucosa** ## General Structure of the Digestive System * **Mucosa:** epithelium, lamina propria, and muscularis mucosae * **Submucosa:** blood vessels, lymphatic vessels, and submucosal (Meissner) plexuses, which contain nerve fibers and neurons of the enteric nervous system * **Muscularis externa:** two or three oblique, circular, and longitudinal muscle layers, which vary from region to region * **Serosa and Adventitia:** covered by serosa, a thin layer of loose connective tissue lined by mesothelium which produces a lubricating fluid that reduces friction during movement of the organs against each other ## Esophagus * **Connects oral cavity to the stomach** * **Function: provide passage for food from the mouth to the stomach** * **Mucous glands** * **Muscularis externa** * **Regions:** * **Upper esophagus:** contains numerous esophageal glands in the submucosa * **Middle esophagus:** esophageal glands in the submucosa are less numerous than in the upper esophagus * **Lower esophagus:** contains large numbers of mucous glands in the lamina propria and submucosa (esophageal cardiac glands) ## Stomach * **"J"-shaped sac (hollow) organ** * **stores food, mixes food with gastric juice, and initiates the processing of food by breaking it down into simpler substances that are easier to digest** * **inner surface:** * **CARDIAC REGION:** change from the nonkeratinized stratified squamous epithelium of the esophagus to the simple columnar epithelium of the stomach * **gastroesophageal sphincter** (lower esophageal sphincter) or cardiac sphincter * **FUNDIC AND BODY REGIONS:** short gastric pits and long branched tubular glands in the lamina propria * **parietal cells and chief cells, along with some stem cells, mucous neck cells, and enteroendocrine cells** * **PYLORIC REGION:** long gastric pits and short, coiled secretory portions * **pylorus sphincter** (pyloric valve) ## Small Intestine * **hollow organ of small diameter that is typically 6 to 7 m long** * **major site for the absorption of nutrients** * **Important features** * **glands (crypts) of Lieberkihn:** * **DUODENUM:** 20 to 25 cm long * **duodenal papillae** (minor and major): * **Brunner glands:** * **JEJUNUM:** 2.5 m long (two fifths of the rest of the small intestine) * **ILEUM:** 4 m long (three fifths of the rest of the small intestine) * **Peyer patches** ## Large Intestine * **hollow organ with a relatively large diameter compared to the small intestine and is about 1.5 m long** * **major site for absorption of water and salts. It also forms, stores, and eliminates feces** * **large numbers of goblet cells in the large intestine** * **CECUM:** small, blind pouch of the large intestine where the ileum connects to the ascending colon * **APPENDIX:** small, blind tube that attaches to the posterior-medial wall of the cecum * **COLON:** ascending colon, transverse colon, descending colon, and sigmoid colon * **RECTUM and ANAL CANAL:** "anorectal junction" ## Diagrams of Digestive System * **Diagram of the Anal Canal:** shows the position of blood vessels, squamous epithelium, submucosa and the muscularis externa. * **Diagram of the Stomach:** shows the position of the gastric pits, neck, middle, and deep regions of the gastric glands, and the submucosa. * **Diagram of the Small Intestine:** shows the position of the goblet cells, epithelium, submucosa, muscularis, and glands. * **Diagram of the Small Intestine:** shows the intestinal villus, epithelium, lamina propria, mucosa, muscularis mucosae and submucosa. You can also see the enterocyte, goblet cell, intestinal crypt, paneth cell, zymogen granules, APUD cell, and duodenal submucosal gland. * **Diagram of the Esophagus:** shows the position of the stratified squamous epithelium, lamina propria, muscularis externa, and esophageal gland.