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The Digestive System Function of the Digestive System Break down food into a “usable” (absorbable) form Supply our cells with the nutrients they need for energy, growth & repair Elimination of waste products Organs of the Digestive System Gastrointestinal tract (GI) – continuous passageway which contains the food from the time it enters the body, until it leaves; organs include: mouth (oral cavity), pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus Accessory organs - participate in digestive processes; organs include: teeth, tongue, salivary glands, liver, gall bladder, pancreas Processes of Digestion 1. Ingestion 2. Movement along GIT Voluntary – e.g. swallowing Involuntary – e.g. peristalsis 3. Secretion – release of water, enzymes, acids, buffers, mucous, etc. into GI tract for physical (mechanical) & chemical digestive processes Processes of Digestion 4. Digestion Mechanical processing – physical breakdown of food; e.g. mastication, mixing waves Chemical digestion – chemical breakdown of food; disassembling of organic molecules into their component parts; requires enzymes carbohydrates monosaccharides proteins amino acids lipids fatty acids Processes of Digestion 5. Absorption – movement of nutrients from GI tract into blood capillaries (monosaccharides, amino acids, H2O, vitamins, minerals) 6. Excretion (Defecation) – removal of waste products from GI tract Histology of the GIT 4 layers of tissue surround the lumen of the GI tract Mucosa Submucosa Muscularis externa Serosa (a.k.a. viseral peritoneum) Mouth (oral cavity) Roof comprised of hard & soft palate; floor primarily comprised of tongue Lips (labia) Tongue that contains papillae (taste buds) taste buds Salivary glands – secrete saliva – made of H2O, salts & “salivary amylase” Parotid duct Parotid gland Sublingual gland Submandibular duct Submandibular gland Teeth – involved in “mastication” (chewing) 2 sets of teeth – deciduous & permanent 4 types of teeth – incisors, cuspids (canines), bicuspids (premolars), molars Parts of a tooth – crown – portion of the tooth that is visible; covered in enamel root – holds the tooth securely in place Pulp – made up of a rich supply of blood vessels and nerves Pharynx (throat) Common passageway for air & food epiglottis protect airway when swallowing (“deglutition”) nasopharynx uvula oropharynx epiglottis laryngopharynx Esophagus (gullet) collapsible tube that leads from pharynx to the stomach functions in “deglutition” through action of peristalsis lower esophageal sphincter (LES) is a ringlike muscle that controls the flow between the esophagus and stomach (prevents stomach contents from flowing back into the esophagus Stomach - Gross Anatomy Lower esophageal (cardiac) sphincter Pyloric sphincter Stomach - Histology Rugae – folds of mucosa & submucosa to allow for expansion of stomach Mucosa of simple columnar epithelium with mucous cells Gastric pit leading to gastric glands Stomach saclike organ composed of the fundus (upper, rounded part), body (main portion), and antrum (lower part). Rugae are the folds in the mucosa lining the stomach. Glands within those folds produces gastric juices that aid in digestion and mucus that forms protective coating of the lining of the stomach Small Intestine - Anatomy - connects stomach to large intestine; 15-20’ long; - site for completion of chemical digestion & absorption of nutrients - comprised of three regions: Duodenum – 10” in length; receives chyme from stomach, secretions from liver, gallbladder & pancreas Jejunum – 8’ long; most digestion & absorption occurs here Ileum – 12’ long; connects to cecum of large intestine at iliocecal valve (sphincter) Small Intestine : Villi – small finger-like projections of mucosal folds across surface of intestine Plicae circulares Pancreas Feather shaped organ located behind the stomach. Both endocrine (secretes insulin & glucagon) & exocrine gland (secretes pancreatic juice) Stomach Tail Body Head Duodenum Pancreatic duct Pancreas Pancreatic juice – mixture of enzymes & buffers (sodium bicarbonate) secreted by acinar cells into pancreatic duct & released into duodenum Liver - Anatomy Largest organ within the body Comprised of 4 lobes Liver & gall bladder Gall bladder – hollow muscular sac under right lobe of liver; stores & concentrates bile; releases bile through cystic duct Right hepatic duct Left hepatic duct Liver - Functions The liver has over 200 functions including (but not limited to): storage of glycogen, fatty acids, fat-soluble vitamins & minerals detoxification & removal of drugs, toxins & hormones phagocytosis of worn-out RBCs, bacteria & other pathogens Large Intestine - Begins at the ilium & ends at the anus; 5’ long; 3” in diameter - main functions – H2O reabsorption; absorption of some vitamins & minerals; formation & temporary storage of fecal material - no chemical (enzymatic) digestion but some bacterial Transverse colon - 3 regions: cecum, colon, rectum Hepatic (rt. Colic) flexure Splenic (lt. colic) flexure Ascending colon Descending colon ileum Ileocecal sphincter Rectum Anal canal Cecum Vermiform appendix Rectum Sigmoid colonanal Internal Anal canal sphincter Rectum External anal sphincter Anus Role of the Large Intestines Feces also known as stools are solid body wastes expelled through the rectum and anus. Gas produced by normal friendly bacteria. The gas that is passes through the body through the rectum is known as flatulence. PATHOLOGY OF THE GI TRACT Disorders of the stomach and esophagus GERD (gastroesophageal reflux disease) upward flow of stomach acid into the esophagus Dysphagia: difficulty in swallowing Pyrosis (“heart burn”) burning sensation caused from return of acidic stomach contents to the esophagus Disorders of the stomach and esophagus (cont) Peptic ulcers: lesion of the mucous membranes of the digestive system Gastric ulcers occur in stomach Duodenal ulcers occur in the upper part of the small intestines (most common form) Eating Disorders Anorexia: lack or loss of appetite for food Bulimia: characterized by episode of binge eating followed by inappropriate behavior such as self-induced vomiting or misuse of laxatives Pica: persistent eating of nonnutritional substances such as clay. Disorders of the Intestines Diverticulitis: inflammation of a pouch or sac occurring in the lining or wall of the intestines IBD (inflammatory bowel disease): chronic inflammatory disease of the GI tract Crohn’s disease: chronic autoimmune disorder causing scarring and thickening of the walls of the intestines. Disorders of the Intestines Intestinal obstruction: complete stoppage or serious impairment to the passage of intestinal contents. Diarrhea: dia (through) rrhea (flow); abnormal frequency of loose or watery stools that can lead to dehydration Constipation: decrease in frequency of the passage of stools Hepatitis Inflammation of the liver usually caused by a virus but may also be caused by a toxic substance. There are 5 varieties of hepatitis: A, B, C, D, E Diagnostic Procedures Enema: a solution is placed into the rectum and colon to clear the bowels in preparation for a procedure Hemoccult: lab test for hidden blood in stools Colonoscopy: direct visual examination of the inner surface of the colon Pharmacology Laxatives: medications or foods given to stimulate bowel movements Acid blockers: which are taken before eating, block the production of acid Antiemetics: prevents or relieve nausea and vomiting.