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Digestive System Function The function of the digestive system is to change complex nutrient molecules that can be absorbed into the blood or lymph to be transported to cells Divisions of digestion 1.The alimentary tube extends from the mouth to the anus. It consist of the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine. 2. The accessory organs of the digestion are the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. Types of digestion 1. 2. Food is broken down in two complementary processes Mechanical digestion is the physical breaking up of food into smaller pieces Chemical digestion uses enzymes to break up food particles, and turn them into something the body can utilize Oral Cavity Food enters the oral cavity by way of the mouth The boundaries are the hard and soft palates, the cheeks, and the floor of the mouth Within the oral cavity are the teeth and tongue Teeth The function of the teeth is to chew Individuals develop two sets of teeth 1) deciduous and 2) permanent Deciduous teeth arrive around 6 months of age, and are a set of 20 teeth Permanent teeth begin to replace deciduous teeth at the age of six, and consist of 32 teeth Teeth Enamel is the hard outer covering of the tooth, and is more resistant to decay than other parts of the tooth Dentin is within the enamel, and is very similar to bone; dentin also forms the root of tooth The innermost portion of a tooth is the pulp cavity, which contains the blood vessels and nerve endings Tongue The tongue is made of skeletal muscle On the upper surface are small projections called papillae, which contain taste buds Sensory nerves for taste are the cranial nerves Elevation of the tongue is the first step in swallowing, and is a voluntary action The mass of food, called a bolus, is pushed backward toward the pharynx Salivary glands Saliva is the digestive secretion in the oral cavity produced by three pairs of glands 1. Parotid glands are just below the ears 2. Submandibular are posterior to the mandible 3. Sublingual are on the floor of the mouth Each gland has at least one duct to take saliva to the oral cavity Cont. Secretion of saliva is continuous, but varies The presence, sight, or smell of food increases the amount saliva Stressful situations decrease the amount of saliva Salivary amylase is the digestive enzyme that breaks down starch molecules Pharynx 1. 2. 3. No digestion takes place in the pharynx, its only related function is swallowing The reflex center for swallowing is the medulla The medulla coordinates: Constriction of the pharynx Closure of the epiglottis Peristalsis of the esophagus Esophagus The esophagus is a muscular tube that takes food from the pharynx to the stomach; no digestion takes place Peristalsis of the esophagus propels food The lower esophageal sphincter relaxes to permit food to enter the stomach, then contracts to prevent backup If contraction is not complete gastric juices may splash up, I.e. heartburn Layers of alimentary tube 1. 2. 3. 4. 4 layers Mucosa Submucosa External muscle layer serosa Mucosa The mucosa, or lining, is made of epithelial tissue and smooth muscle The epithelium secretes mucus, which lubricates the passage of food, and secretes digestive enzymes Submucosa The submucosa is made of connective tissue Meissner’s plexus is the nerve network that regulate secretions Also known as the brain of the gut External muscle layer The external layer has two layers, inner and outer Contractions of the external layer help break up food and mix it with digestive juices Serosa The outermost layer, is fibrous connective tissue The serosa is the mesentary lining the abdominal cavity Stomach 1. 2. 3. 4. The stomach is a sac that extends from the esophgus to the small intestine Both mechanical and chemical digestion take place in the stomach Parts of the stomach: Cardiac is the opening of the esophagus Fundus is the level above the opening Body is the large central portion Pylorus is where most digestion takes place Cont. The folds within the stomach called rugae allow the stomach to stretch without tearing Parietal cells secrete hydrochloric acid, which begins the digestion of proteins Mucus cells secrete mucus, which coats the stomach, and prevents the erosion of gastric juices The pH of the stomach is around 1, which helps to kill microorganisms Small intestine 1. 2. 3. Extends from the stomach to the large intestine The small intestine has 3 parts Duodenum Jejunum Ileum -Digestion is completed in the small intestine -Peyer’s patches are lymph nodes that destroy pathogens in the sm. intestine Liver Consist of two large lobes, right and left The capillaries of the liver are called sinusoids The only digestive function of the liver is the production of bile Bile carries bilirubin and excess cholesterol to the intestines for elimination Bile salts emulsify fats in the small intestine; this a mechanical process The hormone secretin, stimulates the production of bile Gallbladder Is located on the underside of the liver Bile from the liver is stored in the gallbladder until needed Cholecystokinin is the hormone that stimulates the contraction of the smooth muscle in the gallbladder, which forces out bile Gallstones Are caused by cholesterol crystals, that if large enough cannot pass out of the gallbladder The backing up of bile can cause juandice Lithotripsy is the generation of shock waves that break down gallstones into smaller pieces Pancreas Pacreatic enzymes 1. Amylase- digest starch 2. Lipase- converts fats to fatty acids 3. Trypsin- digest polypeptides to amino acids The pancreas also produces bicarbonate juice, which neutralizes the gastric acid that come from the stomach Secretin stimulates the production of bicarbonate juice in the pancreas Disorders of the stomach Pyloric stenosis means that the opening of the pyloric sphincter is narrowed, blocking the emptying of the stomach A gastric ulcer is an erosion of the mucosa of the stomach; it is the result of over secretion of HCl The bacteria Helicobacter pylori causes most gastric ulcers Large Intestine Extends from the small intestines to the anus The first portion is called the cecum; the ileocecal valve prevents fecal matter from back flowing into the small intestine The appendix is attached to the cecum Infection of the appendix caused by the fecal matter is called appendicitis Cont. The last portion of the large intestine is called the colon; no digestion occurs here The only secretion of the colon is mucus that coats for the passage of feces The functions of the colon are the absorption of minerals, water, and vitamins About 80% of the water that enters the colon is absorbed The flora of the colon prevents the growth of pathogens Disorders of the Intestines Duodenal ulcers are erosions of the intestinal wall, caused by gastric juices Lactose intolerance is the inability to digest lacose; when lactose is not digested it undergoes fermentation within the intestine Salmonella is caused by a bacteria found in meats and eggs, they cause the intestines to secrete large amounts of fluid Cont. Paralytic ileus is the ceasing of contraction of the smooth muscle layer of the intestine, causing intestinal blockage Infant botulism is caused by the ingestion of bacterial spores; an infant’s stomach does not produce enough HCl to destroy spores Diets high in fiber have been thought to reduce the frequency of certain diseases Absorption Most absorption takes place in the small intestine Absorption needs a large surface area, projections called villi help increase surface area Elimination of feces Feces consist of cellulose and other undigestible material, and water A spinal cord reflex called the defecation reflex controls the elimination of feces The relaxation of the internal anal sphincter permits defecation to occur The external anal sphincter makes it possible to delay defecation Problems of the Liver Hepatitis is the inflammation of the liver caused by viruses Hepatitis A is an intestinal virus that is spread by the digestion of fecal matter Hepatitis B is contracted by exposure to body fluids of an infected person (blood, semen) Hepatitis C virus is spread through body fluids, blood, and mucus membranes Other Functions of Liver 1. 2. 3. 4. 5. 6. Carbohydrate metabolism- excess glucose is stored as glycogen Amino acid metabolism- amino acids are changed to carbohydrates Lipid metabolism- synthesis of cholesterol Formation of bilirubin- old RBC’s are phagocytized and bilirubin is formed Phagocytosis- phagocytized old RBC’s and bacteria are absorbed by the colon Detoxification- liver enzymes change poisons to less harmful substances