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1/18/2017 Digestive System Main Organs of the Digestive System The main organs of the Digestive System form a tube open at both ends. This tube runs all the way through the ventral cavities of the body. It is called the GI Tract or Alimentary Canal. Wall of the GI Tract 1 1/18/2017 Mouth (Oral Cavity) • Lips Lips • Covered externally by skin • Covered internally by mucous membrane • Cheeks • Tongue + its muscles • Hard + Soft Palates Cheeks • Continuous with the lips in front and lined by mucous membrane which continues with the gums and soft palate. • Formed primarily by the buccinator muscle. This muscle and a generous amount of fat are sandwiched between the outer skin and mucous membrane. • Junction between skin and mucous membrane is VERY sensitive and easily irritated. Tongue The tongue is a solid mass of skeletal muscle components covered by mucous membrane. These muscle fibers are oriented in all directions, giving the tongue extreme maneuverability. 2 1/18/2017 Papillae Rich supply of blood vessels • Taste buds are located on the sides of vallate papillae and fungiform papillae. • Filiform papillae do not contain taste buds. Palates Hard Palate: • made up of parts of 4 bones = 2 maxillae and 2 palatines Soft Palate: • made up of muscle • forms a partition between the mouth and the nasopharynx Cleft Palate Occurs when the roof of the mouth does not completely close, leaving an opening that can extend into the nasal cavity. The cleft may involve either side of the palate and can extend from the front of the mouth (hard palate) to the throat (soft palate). The cleft may also include the lip. The causes of cleft lip/palate are not well understood. Studies suggest that a number of genes, as well as environmental factors, such as drugs (including several different antiseizure drugs), infections, maternal illnesses, maternal smoking and alcohol use and, possibly, deficiency of the B vitamin folic acid may be involved. 3 1/18/2017 Salivary Glands Cleft Lip Parotid – largest – watery (serous) type of saliva (enzymes/ NO mucus) Cleft Palate Submandibular – mixed (compound) glands - enzymes and mucus Sublingual – smallest – only mucus Teeth Types of Teeth Organs of mastication 32 20 “baby” ” teeth 4 1/18/2017 Pharynx Only the terminal portion of the pharynx serves the Digestive System. Esophagus Trachea Esophagus The esophagus begins as an extension of the pharynx in the back of the oral cavity. It then courses down the neck next to the trachea, through the thoracic cavity, and penetrates the diaphragm to connect with the stomach in the abdominal cavity. The esophagus runs through the diaphragm to the stomach. Esophagus The surface of the esophagus must be resistant to trauma, and is, therefore, lined with stratified squamous epithelium. Esophageal hiatus 5 1/18/2017 Hiatal Hernia Esophagus - Sphincters Upper Esophageal Sphincter The UES helps prevent air from entering during respiration. When a hiatal hernia is present, part of the stomach moves up through an enlarged hiatus in the diaphragm. The presence of a hiatal hernia increases the risk for gastroesophageal reflux. Esophagus - Sphincters Lower Esophageal Sphincter (LES) or Cardiac Sphincter Stomach Great example of structure-function! The crisscrossing pattern of muscle fibers makes the stomach a great mixer! 6 1/18/2017 Structure-Function continued … Stomach Gastric pits depressions in the epithelial lining of the stomach. At the bottom of each pit is one or more gastric glands: • • • Reservoir for stored food Churns food Secretes gastric juice: Water, mucus, pepsin, HCl, and intrinsic factor Parietal cells produce • stomach acid and intrinsic factor. • HCl protects body from pathogenic bacteria which has been swallowed Intrinsic factor – binds to vitamin B12 molecules to protect them from digestive juices until they reach the small intestine Chief cells produce the enzymes of gastric juice. Endocrine cells secrete the appetite-boosting hormone ghrelin and the hormone gastrin, which helps regulate digestive function. What is a Peptic Ulcer? • sore on the lining of the stomach or duodenum • • Produces hormones Limited amount of absorption – certain drugs, some H2O, alcohol, and some short-chain fatty acid's in butter or milk fat Small Intestine Helicobacter pylori (H. pylori) is the bacteria which is believed to cause the majority of peptic ulcers. Some ulcers are caused by long-term use of NSAID’s, like aspirin and ibuprofen. In a few cases, cancerous tumors in the stomach or pancreas can cause ulcers. Peptic ulcers are not caused by stress or eating spicy food, but these can make ulcers worse. The bulk of chemical digestion and nutrient absorption occurs in the jejunum! 7 1/18/2017 Small Intestine Great example of structure /function ! Goblet Cells on villi and in crypts secrete mucus. Cells at the base of crypts secrete bactericidal enzymes. Brushborder Arteriole & Venule Large Intestine Wall of the Large Intestine The main function of the large intestine is reabsorption of water. Produces the lubricating mucus that coats the feces as they are formed. 8 1/18/2017 Colonoscopy A test that allows your doctor to look at the inner lining of your large intestine. A barium enema (colon X-ray) is an X-ray exam that can detect changes or abnormalities in the colon. An enema is the injection of a liquid into your rectum through a small tube. A 4-foot thin, flexible tube called a colonoscope is used to look at the colon. The colonoscope has a camera and a light at its tip. A colonoscopy can help find ulcers, colon polyps, tumors, and areas of inflammation or bleeding. A well-lubricated enema tube is inserted gently into the rectum, and then barium contrast material flows slowly into the colon. At certain times, Xray pictures called spot films will be taken of different areas of the colon. Hemorrhoids are enlargements of the veins in the anal canal. Rectum Smooth muscle Rubber Band Ligation for Hemorrhoids - 3D Medical Animation Striated muscle https://www.youtube.com/watch?v=z2hqoeS0oXA Video Hemorrhoids rubber band ligation 1 https://www.youtube.com/watch?v=vT_AsC6qfuw 9 1/18/2017 Appendix Peritoneum A thin membrane that lines the abdominal and pelvic cavities, and covers most abdominal viscera. The functions of the appendix are uncertain. Some scientists believe it serves as a “breeding ground” for intestinal bacteria. The non-pathogenic intestinal flora is thought to help prevent disease and aid in digestion or absorption of essential nutrients. Liver • Removes toxic substances, including alcohol, from the blood. Liver Largest gland in the body! • Secretes bile. • Produces certain blood proteins and serves as a site of hematopoiesis in fetal development. • Involved in the metabolism of carbohydrates, fats, and proteins. • Stores iron, and vitamins A, B12 and D. The intestines are suspended from the dorsal aspect of the peritoneal cavity by a layer of peritoneum called the mesentery. The mesentery connects the small intestine to the posterior abdominal wall. It allows free movement of each coil of the intestine and helps prevent strangulation of the long tube. The liver’s functional units are its lobules. Blood enters the lobules through branches of the portal vein and hepatic artery, then flows through small channels called sinusoids that are lined with primary liver cells (i.e., the hepatocytes). The hepatocytes remove toxic substances from the blood, which then exits the lobule through the central vein (i.e., the hepatic venule). 10 1/18/2017 Liver Bile is produced in the liver by the hepatocytes and secreted into thin channels called bile canaliculi. The canaliculi are drained by bile ducts which then drain into right and left hepatic ducts and eventually into one hepatic duct that carries bile away from the liver. The hepatic duct merges with the cystic duct from the gall bladder to form the common bile duct, which opens into the duodenum. Gallstones are crystallized bile formed in the gallbladder due to an excessive level of cholesterol in the bile. These stones can travel and block the flow of bile resulting in pain in the right upper abdomen. Gall Bladder The gallbladder stores bile + concentrates it 5-10X. During digestion, it contracts and ejects the concentrated bile into the duodenum whenever fatty foods are eaten . Jaundice – yellowish discoloration of the skin resulting from the obstruction of bile flow into the duodenum. Because bile is not allowed out in the feces, it is absorbed into the blood + bile pigments are deposited in the tissues. Pancreas Endocrine gland: Islets of Langerhans produce hormones It is also possible for a small stone to lodge in the opening of the common bile duct into the duodenum. This is a more serious condition where the stone can also block the flow of the pancreatic juice from the pancreatic duct that joins the common bile duct. This may result in pancreatitis (inflammation of the pancreas). Gallbladder problems are very common and if they cause pain, medical attention is usually needed. Alpha cells: Glucagon - raises the level of glucose in the blood Exocrine gland: Acini cells produce digestive enzymes Beta cells: Insulin - stimulates cells to use glucose 11 1/18/2017 I K J 12