Digestive System Module PDF

Ministry of Higher Education Stage: 2nd and Scientific Research Wasit University Module: digestive system College of medicine Lecturer Title : DIGESTIVE SYSTEM MODULE...

Ministry of Higher Education Stage: 2nd and Scientific Research Wasit University Module: digestive system College of medicine Lecturer Title : DIGESTIVE SYSTEM MODULE MUHAMMAD ALBAHADILI 2024-2025  The objectives of the study of digestive system are Outline a general structural plan of the digestive tract Introduce some regional variations in structures that relate to functional adaptations for transport, storage, digestion and absorption Aid understanding of the system’s mechanisms and functions Introduce structural disruption seen in some common disorders and diseases in this system THE GASTROINTESTINAL TRACT ,digestive tract) ,digestional tract ,GI tract ,GIT ,gut (or alimentary canal  What is the digestive system? The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. The digestive system is made up of the gastrointestinal tract and the salivary glands, liver, pancreas, and gallbladder. Functions Regulation of satiety and hunger, mechanical digestion (mastication), swallowing and chemical digestion of food; absorption of necessary nutrients, elimination of unnecessary matter and waste Components Primary organs: mouth, pharynx, esophagus, stomach, small intestines (duodenum, jejunum, ileum), large intestine (colon), rectum and anal canal Accessory organs: salivary glands, liver, gall bladder, pancreas Mouth Contains structures that start digestion: teeth (choping the food), salivary glands (secrete saliva that contain enzymes that start chemical digestion of sugar and fats), tongue (detects taste, pushes bolus towards the pharynx) Pharynx Conducts the food to the esophagus Esophagus Muscular tube that conduct the bolus to the stomach; It has upper sphincter (opens with swallow reflex and allows the bolus to enter the esophagus) and lower sphincter (controls emptying of the esophagus content to the stomach) Stomach Function - secretion of gastric acid (hydrochloric acid + sodium chloride + pepsine) that digests proteins and converts bolus to chyme Parts - cardia (where content of the esophagus empties into stomach), fundus (upper curved part), body (main, central region), pylorus (empties the chyme into the duodenum) Liver Main functions: detoxication of metabolytes, synthesis of proteins, production of biochemicals needed for digestion -> regulation of body's metabolism and energy storage Gallbladder Stores the bile and empties it into the duodenum from where it partially eliminates via defecation Pancreas Secretes insulin when sugar levels are high, secretes glucagon when sugar levels are low, secretes pancreatic juice (tripsinogen, chymotripsinogen, elastase, etc.) into the duodenum where it digests the chyme Small intestines Duodenum - mixes chyme with bile, secretes bicarbonates to rise pH in order to activate pancreatic enzymes which digest the chyme Jejunum - absorbs small nutrients that have been previously digested in duodenum Ileum - absorbs vitamin B12, bile salts and all necessary material that were not absorbed in jejunum Cecum - a pouch that marks division between small and large intestines -> connects the ileum with ascending colon Large intestine Ascending colon - absorbs water from content and moves into the transverse colon by peristalsis Transverse colon - extends from hepatic flexure to the splenic flexure; absorbs water and salts Descending colon - extends from splenic flexure to the sigmoid colon; stores feces that will be emptied into the sigmoid colon Sigmoid colon - contracts to increase pressure inside the colon, causing the stool to move into the rectum Rectum Holds the formed feces awaiting elimination via defecation Anal canal Passage through which undigested food and exfoliated mucosa exit the body Vascularization Supplied by the branches of abdominal aorta: - Celiac trunk - supplies the liver, stomach, spleen, upper 1/3 of duodenum, pancreas - Superior mesenteric artery - supplies distal 2/3 of duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal 1/3 of transverse colon - Inferior mesenteric artery - supplies distal 1/2 of transverse colon, descending colon, sigmoid colon, rectum, anus Innervation Parasympathetic supply - vagus nerve and pelvic splanchnic nerves Sympathetic supply - thoracic and lumbar splanchnic nerves Why is digestion important? Because the body unable to benefit from food and fluid without digestion What is the digestion? The mechanically & enzymatically breaking down food into substances for absorption into the blood stream. Carbohydrate, fat & protein are the main macronutrients need digestion to be absorption  Proteins break into amino acids 9  Fats break into fatty acids and glycerol 10  Carbohydrates break into simple sugars 11  What happens in digestive system? ingestion 12  Digestion Mechanical Mouth Stomach intestine Chemical Mouth Stomach intestine 13  In the mouth 1. Mechanical digestion: The teeth grind up the food. 2.Chemical digestion: Saliva moistens the food and contains enzymes (such as salivary amylase) that start breaking down carbohydrates into sugars. 3.The tongue: moves the food into the throat (pharynx), down the esophagus, and into the stomach. 14  Stomach 1. The stomach muscles physically breaking down the food. 2. The stomach producing enzymes and acids for the chemical breakdown of food. The stomach secreting digestive enzymes and gastric acid to aid in food digestion 3. The stomach releasing food into the small intestine in a controlled and regulated manner. 15  intestine 1. The movement of intestine mix the chyme from stomach with bile from the liver and pancreatic enzymes. 2. Enzymatic digestion from pancreas complete digestion of carbohydrate, fat & proteins 3. Complete the digestion by enzymes from intestine mucosa as a last step of digestion. 16 secretion: about 7500 ml/ day saliva, HCl, bile and a variety of enzymes secreted by exocrine glands. 17 1.Saliva: Produced by salivary glands in the mouth, saliva contains enzymes like amylase that begin the digestion of carbohydrates. 2.Gastric Juice: The stomach secretes gastric juice, which includes hydrochloric acid and pepsin. This acidic mixture helps break down proteins and turns food into a semi-liquid form called chyme. 3.Pancreatic Juice: The pancreas produces enzymes that digest proteins, fats, and carbohydrates. These enzymes are released into the small intestine through the pancreatic duct. 4.Bile: Produced by the liver and stored in the gallbladder, bile helps emulsify fats, making them easier to digest. Bile is released into the small intestine via the bile duct. 5.Intestinal Secretions: The small intestine produces a variety of enzymes that continue the digestion of proteins, fats, and carbohydrates. These secretions also help neutralize the acidic chyme from the stomach. 18 Motility: Muscles of the mouth in mechanical digestion or start the swallowing and movement of food in pharynx and the contractions of the smooth muscles in the walls of the tract, mix and move the ingested food from mouth to anus which is controlled by the nervous system and hormones. Movement in: Mouth Stomach Digestion Digestion Swallowing Controlled chyme to duodenum Pharynx Intestine swallowing Peristalsis Esophagus segmentation 19swallowing  Secretion and motility of the gut are regulated by reflexes in the autonomic nervous system enteric system hormones. They are activated by the contents of the gut and operate to maintain optimum conditions for digestion and absorption. The enteric nervous system is made up of two nerve plexuses in the wall of the gut. What are they?  A dozen or more peptide hormones are released by endocrine Hormones cells in the walls of the gut. Some of these have a paracrine action, others a true endocrine action Paracrine: a hormone that has effects only in the vicinity of the gland secreting it Endocrine: glands release chemical substances (hormones) directly into the bloodstream or tissues. Exocrine: glands release chemical substances through ducts. Absorption: Carbohydrates Glucose, galactose & fructose Fat Triglycerides containing short- and medium-chain fatty acids Glycerol Fatty acid Protein single amino acids and di- or tripeptides Minerals Vitamins water 22 Defecation: is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. colonic mass movement, increased intra-abdominal and rectal pressure, and relaxation of the pelvic floor. 23 24  General Structural features ►Mucosa (M) or mucous membrane ►Submucosa (SM) ►Muscularis externa (ME) ►Serosa (S) or adventitia 25  Mucosa or Mucous Membrane ► Most variable component Composed of: Surface Epithelium Lamina propria (supporting tissue, nerves, vessels, cells of immune system) Muscularis mucosae (thin double layer of smooth muscle);controls local mucosal movement May be flat or folded 26 27 28 29 esophagus duodenum stomach jejunum 30 colon  Submucosa Fibroelastic loose connective tissue; contains vessels & nerves of the submucosal plexus(Meissner’s plexus), wandering leucocytes and fat cells Allows for expansion during the passage of food 31  submucosa 32  Muscularis Externa Two thick layers of smooth muscle; inner circular and outer longitudinal with the myenteric nerve plexus (Auerbach’s plexus) in between Responsible for local movement of the tract and transport along the tract 33  Serosa or Adventitia Serosa and adventitia are two membranous structures that cover the external surface of internal organs. Serosa covers organs that freely move inside a cavity and provides lubrication to reduce friction between organs. Adventitia secures organs in place and is typically found outside of body cavities 34  Adventitia The adventitia is a layer of loose connective tissue (fibrous and/or adipose) covering the external surface of an organ, serving to hold the organ in place and bind it to adjacent tissues and organs. It has no epithelial layer and no distinct boundary; it grades off into adjacent connective tissue, often including the adventitia of adjacent organs. Mouth, pharynx, oesophagus, and rectum 35  Serosa The serosa is a smooth membrane. It consists of a layer of cells and a thin connective tissue layer. The cells secrete serous fluid. Serosa secretes a lubricating fluid to reduce friction due to muscle movement. 36 37  Regional Variation in Structure 38 The mouth Oral mucosa is composed of highly-regenerative stratified epithelium and submucosal connective tissue, which demonstrate accelerated epithelial turnover. 39 the pharynx 1. Mucosa: Epithelium: non keratinized stratified squamous epithelium. Lamina propria: Dense fibrous layer rich in elastic fibres - contains mucous glands. Pharyngeal mucosa lacks muscularis mucosae. Submucosa: lack of submucosa 2. Muscular layer: this is composed of inner longitudinal and outer oblique striated muscle. 3. Fibrous tissue: a thin layer of fibrous connective tissue which connects the pharynx to the adjacent structures (adventitia). 40 Oesophagus (esophagus) Mucosa: non keratinized stratified squamous (NKSS) epithelium prevents wear & tear Submucosa (SM) allows for expansion during the passage of food bolus Mucus-secreting glands (G) lubricate & aid transport 41  Muscularis Externa: Striated muscle fibres in the upper part Smooth muscle for the 2nd & 3rd phase (reflex autonomic) in the lower part of esophagus 42  Regional Variation in Structure for Stomach Mucosa: longitudinal mucosal folds (rugae temporary) 43  Surface epithelium & mucous neck cells (mucosal barrier) The mucosal barrier is the name given to the barrier in the stomach that resists the back-diffusion of hydrogen ions. The barrier is a layer of thick mucus secreted together.with an alkaline fluid 44 ► Cell renewal from gastric glands 45 46  Additional muscle layer (aids movement) Pyloric sphincter at the gastro-duodenal junction (control & regulation of contents) 47  Regional Variation in Structure Small Intestine ► Adapted for digestion & absorption of nutrients. ► Large surface area by the length & structure ► Circular mucosal folds plicae circulares forcing contents to “spiral” (facilitates mixing for digestion & absorption) 48 49  Mucosal villi lined by absorptive cells (ac) with “brush border” (bb) Tubular glands between villi with “stem cells” & local hormone-secreting cells 50  REGIONAL VARIATION IN STRUCTURE LARGE INTESTINE Smooth mucosa Absorptive & mucus-secreting cells 51  Longitudinal muscle reduced & thickened to form “taeniae coli (TC) Tone of circular muscle & the tube’s overall shorter length produces haustrations (sacculation). 52  Large Intestine - Radiology Haustrations (sacculations) 53 54 55  STRUCTURAL DISRUPTION IN COMMON DISORDERS OF THE GIT 56  57 Structural Disruption in Common Disorders of the Oesophagus chronic oesophagitis (reflux of acidic gastric content ; reflux oesophagitis): Increased cell desquamation in compensation by basal cell hyperplasia – causes elongation of connective tissue papillae Lost cells in severe reflux not replaced; ulceration, haemorrhage, perforation and scarring may occur  Barrett’s Oesophagus Results from prolonged reflux due to incompetent lower oesophageal sphincter Metaplastic change in the epithelium; squamous epithelium replaced by columnar cells, which are normally seen in areas of low pH (e.g. gastric epithelium in cardiac or fundic stomach) Premalignant condition  Structural Disruption in Common Disorders of the Stomach Gastritis (inflammation of gastric mucosa) – swollen or erosion of the mucosa Ulceration – persistent erosion; ulcers may haemorrhage, perforate or heal by fibrosis  Gastric mucosa gastritis ulcer Structural Disruption in Common Disorders of the Intestines ► Duodenal ulcers due to acid chyme ulcer ► Coeliac Disease – mucosal villi damage; leads to malabsorption > diarrhoea ► Crohn’s Disease – an inflammatory condition affecting small & large intestine in patches; affects areas with high lymphoid tissue(e.g. terminal ileum) ► Ulcerative Colitis affects only the large bowel mucosa ► Diverticular Disease – outpouching of the mucosa in the descending & sigmoid colon THANK YOU