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Chapter 8 Medical Terminology and Chapter 18 Body Structures The Digestive System Functions of the Digestive System • • • • AKA: alimentary canal, GI tract Intake and digest food Absorption of nutrients from food Elimination of solid waste products Organs • Main – – – – – – – – – Mouth Pharynx Esophagus Stomach Small intestine Cecum Colon Rectum Anus • Accessory – – – – – – – Teeth Tongue Salivary glands Liver Gallbladder Pancreas Vermiform appendix Basics • Digestion – the process of altering the chemical and physical composition of food so that it can be used by the cells in the body • The digestive system is a tube called the alimentary canal or gastrointestinal tract (GI tract) • 29 feet long • Acts like a hallway inside the body • Food must be digested and then absorbed to be used by the cells Process • Digestion – Performed by the organs of the digestive system • Absorption – Performed by the organs of the digestive system • Metabolism – Performed by all the cells in the body Digestion (breakdown of food) • Mechanical – Chewing with teeth – Breakdown in the stomach • Chemical – Action of digestive enzymes – Large molecules reduced to smaller molecules that can be absorbed through the intestinal wall Carbohydrate Digestion • Very little digestion of carbohydrates occurs before it reaches the small intestine • Gastric juices contains no carbohydrate digesting enzymes • Amylase from the pancreas changes starches into sugars – Maltose (malt sugar) – Sucrose (cane sugar) – Lactose (milk sugar) • Intestinal enzymes (maltase, sucrase and lactase) change the sugars into simple sugar or glucose (dextrose) Protein Digestion • Starts in the stomach and is finished in the small intestine • Gastric juice – Rennin (only in infants) – Pepsin – Hydrochloric acid • Every protein molecule is made up of many amino acids – Digestive enzymes split the protein molecule up into single amino acids (finished protein digestion) – Amino acids are referred to as protein building blocks Fat Digestion • Most fats are undigested until emulsification by bile occurs • Then pancreatic lipase splits the fat molecules into fatty acids and glycerin (the end product of fat digestion) Digestive Tract • Wall consists of 4 layers – Mucosa (inside layer) • Produces mucus that protects the wall from the digestive juices and lubricates food passing through – Submucosa • Connective tissue that lies just below the mucosa • Contains many blood vessels and nerves – Muscularis • Two layers of muscle tissue • Cause wave like contractions called peristalsis that moves food through the GI tract • Also assists in mixing of food with digestive juice to further breakdown particles – Serosa • Outer covering composed of visceral peritoneum • Anchored to the posterior wall by the mesentary (large double fold of peritoneal tissue) Mouth • Food enters the GI tract through the mouth • Digestive process begins immediately • Lined with mucous membrane • Hard palate – Bony structure in the anterior formed by maxillary and palatine bones • Soft palate – Above the posterior of the mouth – Consists of muscle – Hanging in the center of the soft palate is the uvula Teeth • • • • • • • • Accessory Organ – Incisors – Canines (cuspids) – Premolars (bicuspids) – Molars (tricuspids) Crown (exposed and visible portion of the tooth) Enamel (hardest tissue in the body) Dentin (makes up the greatest proportion of the tooth shell, found in the root, crown and neck of the tooth) Neck (narrow portion surrounded by gum tissue) Root (fits into the socket of the upper or lower jaw) Chewing – mastication Bolus – food after it’s been chewed forms a rounded mass so that it can be swallowed Salivary Glands • Accessory organ located outside the digestive tube • Three pairs • Saliva contains a digestive enzyme called salivary amylase – Begins the chemical digestion of carbohydrates Pharynx & Esophagus • Pharynx is made of muscle and lined with the mucous membrane • Functions as part of the respiratory and digestive tract • Esophagus or foodpipe is muscular and mucus lined. It connects the pharynx to the stomach • Cardiac sphincter or LES (lower esophageal sphincter) prevents the food from going back up into the esophagus most of the time. • GERD – Gastroesophageal reflux disease • Backward flow of stomach acid up into the esophagus • Causes burning and pressure behind the sternum • Can be stopped by weight loss, avoiding problem foods and beverages, stopping smoking, use of antacids • Hiatal hernia – Common symptom is GERD – Hernia is an organ being pushed through a wall that normally acts as a barrier – The stomach pushes through the hiatus or gap in the diaphragm that allows the esophagus to pass through Stomach • Lies under the diaphragm • Acts as a pouch for food to enter after being chewed and swallowed • Has three divisions – Fundus (enlarged portion to the left and above the opening of the esophagus) – Body (central part of the stomach) – Pylorus (lower narrow section which joins the first part of the small intestine Stomach Cont. • When empty not much bigger than a large sausage but has many folds (rugae) that can expand quite a bit after a large meal • Contractions of the stomach’s muscular walls mix the food with the gastric juices and breaks it down into a semisolid called chyme • Chyme is a continuation of the mechanical digestive process • Peristalsis occurs and moves the food into the small intestine • Disorders – Gastritis – Anorexia – Nausea – Emesis – Ulcer – • crater like wound or sore in the membrane of the stomach caused by tissue destruction • Can cause a burning pain • Most cause by H-pylori bacteria Small Intestine • About 20 feet long • Smaller in diameter than the large intestine – Duodenum – Jejunum – Ileum • Mucous lining contains thousands of microscopic glands that secrete digestive juice • Disorders – Enteritis – Gastroenteritis – Malabsorption syndrome • Failure of the small intestine to absorb nutrients properly • Caused by enzyme deficiencies – Genetic conditions (CF) Liver • Secretes bile into ducts so it is classified as an endocrine gland (largest gland in the body) • Accessory organ • Fats form large globules and must be broken down by bile into smaller particles (emulsification) • The common bile duct drains bile into the small intestine • Disorders – Jaundice (excessive amounts of bile absorbed into the blood when bile can’t be drained from the liver) • Causes yellowing of the skin – Hepatitis • Characterized by jaundice, liver enlargement, anorexia, abdominal discomfort, gray-white feces, dark urine • Caused by alcohol, drugs, toxins, bacterial or viral infections – Cirrhosis • Degenerative liver condition • Caused by hepatitis, chronic alcohol abuse, malnutrition or infection Gallbladder • Located on the undersurface of the liver • Concentrates and stores bile produced in the liver • When chyme that contains lipids (fat) enters the duodenum (first section of the small intestine) it starts the gallbladder contracting by stimulating the secretion of cholecystokinin from the mucosa of the duodenum. The contractions then force bile into the small intestine • Disorders – Cholelithiasis (gallstones) – Cholecystitis (caused from gallstones) Pancreas • • • • Accessory organ Lies behind the stomach An exocrine gland Pancreatic juice is the most important digestive juice – Contains enzymes that digest all three major kinds of food – Also neutralizes hydrochloric acid – Enters the duodenum the same place bile enters • Disorders – Diabetes mellitus – Pancreatitis Large Intestine • About 5 feet long • Forms the lower portion of the digestive tract • Cecum – pouch-like area • Ascending colon – food flows upward on the right side of the body • Transverse colon – extends across the front of the abdomen from right to left • Descending colon – runs downward on the left side • Sigmoid colon – S-shaped segment that attaches to the rectum • Rectum – storage pouch • Anal canal – end portion of the rectum that ends at the external opening Large Intestine • Undigested & unabsorbed food enters the large intestine after passing through the ileocecal valve • Chyme found in the small intestine becomes fecal matter in the large intestine as water and salts are reabsorbed • Bacteria in the large intestine release other nutrients and are responsible for the synthesis of vitamin K and the production of some B-complex vitamins • Passage of food through the large intestine takes 3 to 5 hours Disorders of the Large Intestine • Diarrhea – – – • Constipation – – • Any inflammatory condition of the large intestine Symptoms are diarrhea, abdominal cramps or constipation, bleeding and intestinal ulcers Can be caused by emotional stress, (IBS), autoimmune disease May be corrected by surgically removing the affected portions of the colon Crohn’s Disease – • Inflammation of abnormal saclike outpouchings of the intestinal wall Often found in adults over 50 who eat a low fiber diet Colitis – – – – • Decreased intestinal motility Feces lose volume as water is absorbed which reduces the stimulation of the bowel emptying reflex resulting in more fecal retention Diverticulitis – – • When contents move quickly and fluids can’t be reabsorbed Often caused by bacteria or parasites Because of the water loss involved untreated diarrhea may quickly lead to dehydration and possible death Autoimmune colitis that also affects the small intestine Colorectal cancer – – – Occurs most frequently in adults after age 50 and more common in men Second leading cause of death from cancer in the US and 4th most common type of cancer after prostate, breast, and lung Diagnosed during a visual exam during a sigmoidoscopy or colonoscopy Appendix • Vermiform appendix – Vermis (worm shape) – Contains lymphatic tissue and may play a minor role in immunologic defense mechanisms – Directly attaches to the cecum – Inflammation is appendicitis and can be evaluated by a digital rectal exam because it’s very close to the rectal wall – If infection persists the appendix may rupture and release infection into the abdominal cavity causing infection of the peritoneum and other internal organs which can cause death Peritoneum • Sheet of serous membrane that lines the abdominal cavity and covers the organs located in it including most of the digestive organs • The parietal layer of the peritoneum lines the abdominal cavity • The visceral layer covers the abdominal organs • Peritonitis – Usually a result from bacterial infection, often from a ruptured appendix – Characterized by abdominal distension, pain, nausea, vomiting, tachycardia, fever, dehydration – Circulatory shock and heart failure may result colonoscopy Laparoscopic cholecystectomy appendectomy hepatectomy