9_Digestive System_Main Organs.pptx

Digestive System – Part 1 Chapter 21, Human Anatomy (LibreTexts) “Digestive System Diagram” by Mariana Ruiz is in the Public D omain CC0. Functions of the Digestive System 1. Ingestion = Take in food & drinks 2. Digestion = breakdown of food into small structures and molecules • Mechanical dig...

Digestive System – Part 1 Chapter 21, Human Anatomy (LibreTexts) “Digestive System Diagram” by Mariana Ruiz is in the Public D omain CC0. Functions of the Digestive System 1. Ingestion = Take in food & drinks 2. Digestion = breakdown of food into small structures and molecules • Mechanical digestion = physical breakdown by teeth, tongue, muscles • Chemical digestion = breakdown using enzymes 3. Motility = movement of food and drinks 4. Secretion = production and release of products to aid digestion 5. Absorption = movement of nutrients and water across GI tract into blood and lymph vessels 6. Elimination = get rid of waste Main Structures of the Digestive System • Gastrointestinal (GI) tract (also called digestive tract or alimentary canal) is a tube formed by the following main digestive organs: • • • • • • • • oral cavity Pharynx Esophagus Stomach small intestine large intestine Rectum Anus Accessory Structures of the Digestive System • Accessory digestive organs are not part of the digestive tract but are connected to it and assist in digestion. • • • • • • Salivary glands Teeth Tongue Liver Gallbladder Pancreas Structures of the Digestive System "Components of the Digestive System" by OpenStax is licensed under CC BY 3.0 Motility in the GI Tract • Mastication (chewing) is the movement performed by teeth and tongue in the oral cavity to mechanically break down foods and mixing it with the saliva • Swallowing is the movement performed by tongue and pharynx to push foods and drinks in the esophagus • Churning is the squeezing that occurs in the stomach to mechanically breakdown food and mixing it with digestive juices. • Segmentation is the rhythmic movement of GI tract to mix food with digestive enzymes. Does not produce movement forward. Occurs mainly in small intestine • Peristalsis is made by waves of contractions along the GI tract (esophagus to anus) that push the material forward. Peristalsis “Peristalsis” by OpenStax is licensed under CC BY 3.0 Peritoneum • Abdominopelvic cavity is lined with moist serous membrane called peritoneum that holds digestive organs in place through a series of folds called mesenteries that contain blood vessels and nerves. • Made of: • Parietal peritoneum lines inside of abdominal cavity • Visceral peritoneum covers surface of abdominal organs (also known as serosa) • Peritoneal cavity is between peritoneal layers and contains serous fluid • Intraperitoneal organs are completely surrounded by visceral peritoneum: all non-retroperitoneal digestive organs • Retroperitoneal organs are not covered or not completely covered by peritoneum: esophagus, pancreas, last part of duodenum, ascending and descending colon, rectum Mesenteries • Greater omentum: Apron-like structure that lies superficial to the small intestine and transverse colon; a site of fat deposition in people who are overweight. • Lesser omentum: Suspends the stomach from the inferior border of the liver; provides a pathway for structures connecting to the liver. • Mesentery proper: Vertical band of tissue anterior to the lumbar vertebrae and anchoring all of the small intestine except the initial portion (duodenum). • Mesocolon: Attaches two portions of the large intestine (the transverse and sigmoid colon) to the posterior abdominal wall. Midsagittal View of the Peritoneum “Midsagittal View of Peritoneum" by KL Nguyen is a derivative from the original work of Daniel Donnelly is licensed under CC BY 4.0; Anterior View of Omentum “Anterior View of Omentum" by KL Nguyen is a derivative from original work of Daniel Donnelly is licensed under Mesocolon “Mesocolon" by KL Nguyen is a derivative from the original work of Daniel Donnelly is licensed under CC BY 4.0 Organization of the GI Tract - I From innermost to outermost, 4 layers: 1. Mucosa contains fenestrated capillaries and lymphatic capillaries called lacteals. Made by • Epithelium that lines the lumen; contains goblet cells; subtype changes through GI tract • Lamina propria: areolar connective tissue containing MALT • Muscularis mucosae: thin layer of muscle that creates folds in stomach and small intestine to increase surface area 2. Submucosa contains mucin-secreting glands to help with peristalsis, blood and lymph vessels, nerves. Made by areolar or dense irregular connective tissue. Organization of the GI Tract - II 3. Muscularis is made by two layers of smooth muscle tissue: a inner circular layer and an outer longitudinal layer. Thickening of inner layer forms sphincters that open or close a passageway. Myenteric nerve plexus originates from vagus nerve and controls contractions. • Exception: mouth, pharynx, upper esophagus and external anal sphincter have skeletal muscles • Exception: stomach has a third layer, oblique smooth muscle layer • Exception: large intestine has 3 bands of longitudinal smooth muscles called teniae coli 4. Serosa (for intraperitoneal organs, also called visceral peritoneum) or Adventitia (for retroperitoneal organs) is made by areolar connective tissue. Layers of the Alimentary Canal "Layers of the Gastrointestinal Tract” by OpenStax is licensed under CC BY 3.0 Main Structures of Oral Cavity - I • Functions: ingests food, chews and mixes food, begins chemical breakdown of carbohydrates and lipids, moves food into the pharynx • Oral cavity is the teeth and area within them • Oral vestibule is the space between cheeks or lips and gums • Cheeks end at labia (lips) which are formed by skeletal muscle (orbicularis oris) covered with keratinized stratified squamous epithelium. The reddish hue from abundant blood vessels. • Gingivae (gums) are made of dense irregular connective tissue, with layer of non-keratinized stratified squamous epithelium • Superior and inferior labial frenulum attaches internal surfaces of lips to gingivae Main Structures of Oral Cavity - II • Palate is the roof of oral cavity and separates it from nasal cavity • Hard palate is anterior 2/3 of palate and is made by bones (maxilla and palatine) covered with nonkeratinized stratified squamous epithelium. Has transverse palatine folds that help manipulate food. • Soft palate is posterior 1/3 of palate and is made by skeletal muscle covered with non-keratinized stratified squamous epithelium. Ends in uvula. Uvula and soft palate elevate during swallow to block nasal cavity. Structures of the Mouth “Structures of the Mouth” by OpenStax is licensed under CC BY 3.0 Accessory Structures of Oral Cavity: Tongue • Helps make sounds. • Manipulates and mixes food during chewing creating bolus, soft moist ball of food and saliva; pushes bolus to oropharynx for swallowing. • Primarily skeletal muscle covered with non-keratinized stratified squamous epithelium. It has papillae to add texture and surface area. It is attached to floor of oral cavity by lingual frenulum. Tongue “Tongue” by OpenStax is licensed under CC BY 3.0 Accessory Structures of Oral Cavity: Salivary Glands • Secrete saliva = 95% water mixed with ions, enzymes, antibodies, and growth factors. • Saliva moistens food, cleans and lubricates oral cavity, dissolves food particles for taste. • Submandibular salivary glands produce 60-70% of saliva • Parotid salivary gland produces 25-30% of saliva. Swollen during mumps. • Sublingual salivary glands produces 3-5% of saliva Salivary Glands “Salivary Glands” by OpenStax is licensed under CC BY 3.0 Accessory Structures of Oral Cavity: Teeth • Collectively called dentition • Crown is exposed part made of enamel (hardest substance in body) • Neck is region just within gums, made of dentin • Root anchors tooth to bone with periodontal ligaments that fit in dental alveoli on mandible and maxilla bones. Contains a root canal that opens up into connective tissue through apical foramen. • Center of tooth and root is the pulp cavity which contains nerves, arteries and veins. Tooth “Tooth” by OpenStax is licensed under CC BY 3.0 Types of Teeth • 20 Deciduous teeth (baby teeth) that start to erupt at 6 months old • 32 Permanent teeth that replace the deciduous teeth • • • • • 4 central incisors: for cutting 4 lateral incisors: for cutting 4 canines: for puncturing and tearing 8 premolars: for crushing and grinding 12 molars: for crushing and grinding Permanent and Deciduous Teeth “Permanent and Deciduous Teeth” by OpenStax is licensed under CC BY 3.0 Pharynx • Functions: Propels food to next organ/region • Oropharynx and Laryngopharynx are made of nonkeratinized stratified squamous epithelium • (Nasopharynx is only part of respiratory system) Pharynx “Pharynx” by OpenStax is licensed under CC BY 3.0 Esophagus – Main Features • Functions: Propels food to next organ/region • Location: posterior to trachea and anterior to vertebral column • At most superior end, the esophagus connects to pharynx at superior esophageal sphincter which closes during inhalation. • At the most inferior end, the esophagus connects to the stomach at esophageal hiatus which works with diaphragm to prevent reflux from stomach. An inferior esophageal sphincter prevents movement of food back up esophagus. Esophagus - Histology • Mucosa has thick, non-keratinized stratified squamous epithelium to withstand abrasions of bolus • Submucosa has lots of elastic fibers to stretch during swallowing and mucous glands to provide lubricating mucus • Muscularis has two layers (skeletal and smooth muscles) • Adventitia (retroperitoneal organ) Esophagus “Esophagus” by OpenStax is licensed under CC BY 3.0 Stomach – Main Features • Functions: • Mechanical digestion: mixes and churns food with gastric juices to form chyme • Chemical digestion of proteins • Motility: releases chyme into the duodenum • Absorption of some fat-soluble substances (for example, alcohol, aspirin) • 4 Regions: • Cardia: distal to lower esophageal sphincter. Opening of stomach is called cardiac orifice. • Fundus: lateral and superior to cardiac orifice • Body: largest part of stomach • Pylorus (or pyloris): funnel-shaped pouch. Opening into duodenum called pyloric orifice surrounded by pyloric sphincter. Stomach “Stomach” by OpenStax is licensed under CC BY 3.0 Stomach – Histology • Mucosa has simple columnar epithelium that folds into rugae to increase surface area for digestion of bolus. Gastric pits are indentations in lining where cells secrete digestive enzymes, hormones, hydrochloric acid and mucus (to protect themselves from the acid) At the base of gastric pits are gastric glands that release gastric juices (1 L of bolus becomes 3-4 L of chyme) • Submucosa • Muscularis has 3 muscle layers (inner oblique, middle circular and outer longitudinal) to ensure plenty of churning • Serosa (intraperitoneal organ) Histology of the Stomach “Histology of the Stomach” by OpenStax is licensed under CC BY 3.0 Small Intestine – Main Features • Functions: • Mechanical digestion through segmentation that mixes chyme with digestive juices • Chemical digestion of carbohydrates, proteins, and fats with intestinal and pancreatic enzymes • Motility: peristalsis to propel food into large intestine • Absorption of nutrients into blood capillaries or lacteals • Small in diameter but long in length compared to large intestine • Extends from pylorus of stomach to cecum of large intestine • 3 regions • Duodenum: mostly retroperitoneal • Jejunum: intraperitoneal, suspended by mesentery proper • Ileum: intraperitoneal, suspended by mesentery proper; ends at ileocecal valve Small Intestine “Small Intestine” by OpenStax is licensed under CC BY 3.0 Small Intestine - Histology • Mucosa has simple columnar epithelium with microvilli and goblet cells. Epithelium folds into intestinal villi to create lots of surface area for absorption. Intestinal villi fold into circular folds to slow down passage of chyme and increase absorption. Each intestinal villus contains blood capillaries and lacteals for the transport of nutrients. Intestinal glands (or intestinal crypts) sit between the intestinal villi and produce digestive enzymes and hormones. Mucosa also has MALT called Peyer’s patches. • Submucosa contains lymph vessels, arterioles and venules • Muscularis has two layers • Adventitia for duodenum; Serosa for jejunum and ileum Histology of Small Intestine Micrographs provided by the Regents of University of Michigan Medical School © 2012. “Histology of Small Intestine ” by OpenStax is licensed under CC BY 3.0 Large Intestine – Functions • Functions: • Mechanical digestion through segmentation to further break down chyme • Chemical digestion through fermentation by bacteria • Absorption of most residual water, electrolytes, and vitamins • Motility through peristalsis to propel feces toward rectum • Elimination of feces Large Intestine – Main Features • “Large” in diameter, short in length compared to small intestine • 4 main regions • Cecum with vermiform appendix • Ascending colon: retroperitoneal • Transverse colon: intraperitoneal suspended by transverse mesocolon • Descending colon: retroperitoneal • Sigmoid colon: intraperitoneal suspended by sigmoid mesocolon • Rectum with rectal valves: retroperitoneal • Anus with internal and external anal sphincters Large Intestine “Large Intestine” by OpenStax is licensed under CC BY 3.0 Large Intestine – Histology • Mucosa has simple columnar epithelium with microvilli and many goblet cells, except for anus that is lined with non-keratinized stratified squamous epithelium. Intestinal glands are present, as well as bacterial flora. • Submucosa • Muscularis: longitudinal layer of muscle forms 3 thin bundles called teniae coli that cause the colon to bunch up into haustra • Serosa/Adventitia Histology of Large Intestine Micrograph provided by the Regents of University of Michigan Medical School © 2012. “Histology of Large Intestine ” by OpenStax is licensed under CC BY 3.0 Teniae Coli and Haustra “Teniae Coli Haustra Epiploic Appendage” by OpenStax is licensed under CC BY 3.0