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Digestive System Digestion-Mechanical & chemical breakdown of food into forms that cell membranes can absorb Alimentary Canal-wall structure-4 layers 1. Mucosa-Mucus membrane, has folds and projections in lumen to increase absorbing area, protects tissue beneath it. The mucosa carries out secretion, digestion, and absorption and consists of epithelial cells 2. Submucosa- has blood vessels that nourish surrounding tissue and carry away absorbed materials. Lymphatic vessels carry fatty acids to the blood vessels, and pathogenic organisms to lymph nodes. The vessels are held in place by loose connective tissue 3. Muscular Layer- 2 coats of smooth muscle, circular fibers contract, causing diameter to decrease. Longitudinal fibers contract and the alimentary canal shortens 4. Serosa-outer covering of the tube. Cells secrete serous fluid which moistens outer surface of the tube so that organs in the abdomen slide freely against one another. This layer is known as the visceral peritoneum. • Movements of the tube 1. Mixing- in the stomach Smooth muscles move rhythmically to mix food with digestive enzymes and acid. Sphincters at both ends of the stomach close to keep chyme in stomach. 2. Propelling-peristalsis Circular smooth muscles contract, narrowing the tube. As the contraction moves down the tube, it pushes food in front. Simultaneously, muscle in front of the food relax, opening the tube and allowing food to enter. Organs 1. Mouth- chewing begins digestion by mechanically breaking down food and mixing it with saliva. 2. Cheeks and Lips contain muscles and sensory receptors used to determine temperature and texture of food. 3. Tonguea. frendulum Membrane which connects the center of the tongue to the floor of the mouth. b. papilla Rough projections which help tongue move food. They also contain taste buds. c. lingual tonsils Rounded mass of lymphatic tissue found at the back of the tongue where it attaches to the hyoid bone. 4. Palate Roof of mouth consists of the anterior hard palate and the posterior soft palate, which extends to the cone-shaped uvula. 5. Uvula is pulled up during swallowing, closing off the nasal cavity from the pharynx 6. Palantine Tonsils Lymphatic tissue found in the back of the throat below the soft palate 7. Pharyneal Tonsils-adenoids Lymphatic tissue on the posterior wall of the pharynx above the soft palate. The lymph tissue is important in fighting infection. Teeth 1. Primary-Deciduous teeth These teeth erupt through the gums between 6 mo. and 4 years. The teeth are temporary and fall out. There are 20 deciduous teeth, 10 in the upper set, 10 in lower jaw. 2. Secondary-Permanent teeth push the primary teeth out of their socket, or erupt in a new socket. There are 32 secondary teeth. Incisors Chisel-shaped teeth used to bite off pieces of food Cuspids Cone-shaped teeth used to grasp and tear food Biscuspids and molars have flattened surfaces and are used to grind food particles 2 portions to each tooth 1. Crown the portion of the tooth which projects above the gum 2. Root the portion of the tooth anchored into the jaw Dentin is beneath the enamel and is composed of bonelike material, although it is harder. Cementum is a thin layer of bonelike material which surrounds the root. Peridontal Ligament surrounds cementum and consists of collagenous fibers attaching tooth to jaw. Pulp cavity contains blood vessels, nerves, and connective tissue (pulp) which extend into the root canal Salivary glands secrete saliva, which begins the chemical digestion of carbohydrates Parotid gland are below the ear, and secrete a watery fluid rich in amylase Submandibular gland is just above the mandible. The gland has some mucous cells, making it’s secretions more viscous Sublingual gland is below the tongue and consists primarily of mucous cells. Their secretions are thick and stringy Pharynx is a cavity posterior to the mouth and has 3 parts Nasopharynx is an extension of the nasal cavity, & allows air to pass through Oropharynx is posterior to the soft palate and is the passageway for food leaving the mouth Laryngopharynx is inferior to the oropharynx and is the passageway leading to the esophagus Esophagus is a collapsible tube lined with mucous glands, which secrete mucous to moisten and lubricate the tubes lining Stomach is J shaped, with folds called rugae which contain mucosal and submucosal layers. Contraction of the outer muscle layer helps mix food with stomach secretions. Cardiac is the small region of the stomach near the opening to the esophagus Fundic balloons above the cardiac region & is a temporary storage area for food Body region is the main part of the stomach and lies between the fundic and pyloric regions Pyloric region is adjacent to the small intestine and contains the pyloric sphincter c Stomach secretions: inner lining of the stomach is the mucous membrane which is studded with gastric pits which are at the end of the tubular gastric glands. The glands consist of 3 types of secretory cells. Mucus cells or goblet cells secrete mucus which coats and protects the stomach wall from HCl Chief cells secrete pepsinogen which is converted to pepsin by HCl. Pepsin breaks down proteins Parietal cells secrete HCl The 3 products together make up gastric juice Gastrin is an important digestive hormone which increases secretions from the gastric glands Absorption is the movement of substances across the cell membrane into the cell Peptic ulcers are open sores in the mucous membrane of the GI tract Gastric ulcers are ulcers in the stomach Duodenal ulcers are in the small intestine nearest the stomach For many years, ulcers were attributed to stress. Helicobacter pylori, a bacteria growing in the stomach was found to cause gastric ulcers which can be cured with antibiotics in combination with acid-lowering drugs. Stomach muscle contraction is used for mixing food, producing a semi-liquid paste called chyme which accumulates near the pyloric sphincter. Then the pyloric sphincter muscle begins to relax, allowing the chyme to enter the duodenum. The amount of time the chyme remains in the stomach varies. Liquids pass through the stomach rapidly, but solid food remain in the stomach until they are completely mixed with gastric juice fatty foods remain in the stomach 3-6 hours proteins are kept in the stomach or < 3 hours carbohydrates pass through the stomach faster than fatty foods & proteins Pancreas has acinar cells that make up most of the organ. The cells surround a tube, into which they release their secretions. Many of these tubes merge to form the pancreatic duct, which carries the secretions to the duodenum. Pancreatic juice contains enzymes that digest proteins, carbohydrates, and nucleic acids. Pancreatic Enzymes 1. Pancreatic amylase breaks down starch and glycogen into disaccharides 2. Lipase breaks triglycerides into fatty acids and glycerol 3. Trypsin, chymotrypsin, carboxypeptidase break down proteins. These enzymes are secreted in an inactive form until activated by an enzyme (enterokinase) in the small intestine If trypsinogen is converted to the active enzyme trypsin in the pancreas, it starts to digest the pancreas. This condition is called pancreatitis, and occurs if the bile duct becomes blocked. Blockage is caused by alcoholism, gallstones, infections, traumatic injury, or side effects of some drugs. Secretin is a hormone that stimulates secretion of pancreatic juice, which has a high concentration of bicarbonate ions, which neutralize the acid of chyme, preventing ulcers. Pancreas destroyed by pancreatitis Liver- consists of two lobes, right and left. The functional units are called lobules which consist of hepatic cells radiating outward from a central vein. Hepatic sinusoids separate groups of cells and supply them with nutrients brought directly from the intestine by the hepatic portal vein. Functions of the liver 1. When blood sugar levels are high, glucose is absorbed by the liver and converted to glycogen. This is reversed as blood glucose levels drop. These actions are controlled by two hormones, insulin and glucagon. 2. Converts excess food to fats which are sent to adipocytes for storage. Proteins are also metabolized by the liver. 3. Kupffer cells (stationary phagocytes) remove bacteria and other foreign particles by phagocytosis. Removes and destroys damaged red blood cells. 4. The liver is the major detoxification unit of the body. Toxins are broken down and prepared for excretion. Lipid soluble toxins are metabolized into water soluble materials (so they do not diffuse across the intestinal cell membrane). Metabolized toxins are secreted with the bile Remember that the hepatic portal vein brings blood directly to the liver from the intestine. Makes sense, doesn’t it! Bile yellow/green liquid made up of bile salts, bile pigments (bilirubin), cholesterol, and electrolytes including metabolized toxins. Bile is stored in the gallbladder. Bile salts break fat into smaller droplets ( emulsification) so they can be more effectively digested. Bilirubin is a breakdown product of hemoglobin which is secreted in the bile. Jaundice turns the skin and eye whites yellow. This is due to the build-up of bilirubin. Jaundice is caused by 1. liver disease (hepatocellular jaundice), 2. blockage of the bile duct (obstructive jaundice), or 3. rapid breakdown of RBC (hemolytic jaundice). Person w/ Jaundice Gallbladder • Hepatitis is an inflammation of the liver, caused by a virus. • Hepatitis A is spread by objects contaminated with infected feces. This is a mild form of the disease. • Hepatitis B is transmitted by body fluids (blood transfusions, shared needles, sexual activity). • Hepatitis C accounts for >50% of all hepatitis cases. It is transmitted in blood (shared needles etc and from mother to fetus). Often it is a chronic disease. • Hepatitis D occurs in those infected with hepatitis B. >20% die. Liver destroyed by hepatitis. Note the normal piece of liver to the far right. Hepatitis E is transmitted in water contaminated by feces. Problem for visitors in 3rd world countries. Gall stones- cholesterol in bile may form crystals that enter the common bile duct & cause severe pain. The stones can be removed surgically. Sometimes, doctors use ultrasound to break up stones. The fragments can than pass through the ducts. Patients who persistently form gall stones may have the gallbladder removed. What problem do you think this can cause? What do you think these people are forced to do?