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Chapter 15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DIGESTIVE SYSTEM AND NUTRITION Microorganisms that live in our digestive system are key to maintaining our health They break down plant sugars we cannot They also make vitamins K and B12 They break down toxins and drugs They may aid in metabolism FUNCTIONS OF THE DIGESTIVE SYSTEM Mechanical and chemical breakdown of food Absorption of nutrients Alimentary canal mouth to anus - 8m long ALIMENTARY CANAL CANAL WALL STRUCTURE 4 LAYERS 1) mucosa - glands that secrete mucus and digestive enzymes 2) Submucosa - loose connective tissue, glands, vessels, nerves 3) Muscular layer circular and longitudinal fibers (outer layer) 4) Serosa - seran wrap around alimentary canal MOVEMENTS OF THE DIGESTIVE SYSTEM Mixing - rhythmic contraction of smooth muscles to mix food and digestive enzymes Segmentation alternating contraction and relaxation of smooth muscle Peristalsis - propelling contents in a wavelike motion THE MOUTH Mechanically reduces solid particles Cheeks and lips support the mouth movements The tongue is skeletal muscle that mixes food with saliva and pushes a bolus to the pharynx Papillae - provide friction to move food Lingual tonsils - root of tongue posteriorly lymphatic tissue THE PALATE Roof of the oral cavity Hard palate - bony anterior part Soft palate - muscular posterior part Uvula - muscular arch of the soft palate Palatine tonsils lymphatic tissue on either side of the tongue - common infection site Pharyngeal tonsils posterior wall of the pharynx THE TEETH Primary teeth six months to four years - 20 of them -shed in the order they appeared Secondary teeth - 32 of them push out the primary teeth out of sockets at 6 years of age - molars 17-25 years of age A TOOTH IN DETAIL Enamel covers the crown is not replaced Dentin beneath the enamel covers the pulp cavity with the vessels and nerves Cementum encloses the root and the periodontal ligament surrounds the cementum Flossing prevents breakdown of the periodontal ligaments A root canal is how the vessels enter the pulp cavity and is removed with the treatment that has the same name when a tooth is severely damaged SALIVARY GLANDS Secrete saliva and moisten food to start carbohydrate digestion Dissolves food to aid in tasting it and cleanses the mouth and teeth Serous cells - watery fluid salivary amylase Mucous cells - mucus that binds food particles and lubricates food Saliva is produced when we see, smell or think about food PHARYNX AND ESOPHAGUS Important passageways that aid in swallowing Pharynx - connects the nasal and oral cavities Nasopharynx - passageway for breathing Oropharynx - passageway for food to move down from the mouth Laryngopharynx - passageway to the esophagus THE PROCESS OF SWALLOWING 3 STAGES 1) Food is chewed voluntarily, mixed with saliva and a bolus is forced into the pharynx 2) Sensory receptors in the pharyngeal opening recognize the presence of a bolus and trigger the swallowing reflex -Soft palate rises (so no food up the nose) - Hyoid bone and larynx elevate, epiglottis closes over larynx -Tongue presses against soft palate -Longitudinal muscles of the pharyngeal wall contract -Lower pharynx relaxes to open the esophagus -Waves force food into the esophagus 3) Peristaltic movements transport the food from the esophagus to the stomach PARTS OF THE STOMACH GASTRIC SECRETIONS Chief cells - secrete digestive enzymes Parietal cells - secrete hydrochloric acid Pepsinogen - released from chief cells turns to pepsin when contacts HCl Pepsin breaks down proteins Mucous cells prevent the digestive lining from digesting itself Intrinsic factor - secreted by parietal cells helps B12 absorption in the small intestine REGULATION OF GASTRIC SECRETIONS Starts with the sense of food Vagus nerve stimulates Ach release Ach gets the gastric juice flowing HCl and pepsinogen plus gastrin (replaces damaged mucosal cells) are released As food enters the duodenum proteins and fats cause cholecystokinin to be released and motility slows to allow filling of the small intestine with food GASTRIC ABSORPTION Stomach absorbs small amounts of water, certain salts and lipid soluble drugs and alcohol After mixing in the stomach a paste of digestive juice and food is made = chyme Stomach contractions push small amounts of chyme into the small intestine via a pyloric sphincter Liquids and carbohydrates pass through the stomach quickly Fats take the longest to get through the stomach Proteins a bit less time than the fats Once chyme enters the duodenum the pancreas, liver and gall bladder add their secretions THE PANCREAS Endocrine and exocrine function Exocrine - pancreatic juices stimulated by secretin from the duodenum Pancreatic acinar cells release the juices into tiny ducts that flow into the pancreatic duct The pancreatic duct connects with the duodenum where the bile duct form the liver connects in = hepatopancreatic sphincter Pancreatic amylase - splits carbohydrates Pancreatic lipase - breaks down triglycerides (fats) Nucleases - break down nucleic acid molecules Trypsin, chymotrypsin and carboxypeptidase break down proteins Enterokinase activates the “sinogen” forms of the above enzymes Figure 15.15 THE LIVER -A fibrous capsule encloses the liver and connective tissue divides the organ into lobules -Each lobe has small hepatic lobules -The lobule has hepatic cells radiating from a central vein -Blood from the digestive tract is brought to the liver via the hepatic portal vein to enter the sinusoids - FUNCTION: carb metabolism to maintain glucose concentrations; the liver stores glucagon and breaks it down to glucose when needed HEPATIC LOBULE AND SINUSOIDS Kupffer cells are on the inner lining of the sinusoids and remove bacteria and invaders from the portal vein Blood goes from the sinusoids to the central vein and exits the liver Bile canaliculi carry secretions from hepatic cells to bile ductules which join to form heaptic ducts and join to form the common hepatic duct Figure 15.18 HEPATITIS Inflammation of the liver Symptoms: mild headache, low fever, fatigue, lack of appetite, nausea and vomiting, stiff joints. After the 1st week: rash, pain in the upper right quadrant, dark foamy urine, pale feces, yellow sclera and skin. Fulminant hepatitis - rare where sever symptoms come with altered behavior and personality. If this person is not treated promptly kidney failure, liver failure or death can result. Hepatitis A-G Hep A - food or objects with the virus in them Hep B - body fluids, blood transfusions, hypodermic needles Hep C - half of all cases, blood transfusions, sharing razors or needles Hep D - in those with Hep B - via transfusion or IV drug use Hep E - water contaminated with feces Hep G - rare; found in those with fulminant hepatitis BILE AND THE GALLBLADDER Bile - yellow-green pigment secreted from hepatic cells Bile contains bile salts, pigments (bilirubin/verdin), cholesterol and electrolytes Bile pigments are breakdown products of hemoglobin from RBCs - Obstructive jaundice -> blocked ducts - Hepatocellular jaundice -> liver is diseased - Hemolytic jaundice - RBCs are destroyed rapidly from transfusion or blood infection like malaria GALLBLADDER - Pear-shaped sac on the inferior aspect of the liver - Lined with epithelial cells and has a muscular layer, stores bile and reabsorbs water to concentrate bile - Contracts to release bile into the small intestine Cystic duct - joins the common hepatic duct to form the common bile duct The cystic duct heads into the duodenum at the hepatopancreatic sphincter Bile backs up into the cystic duct when the sphincter is closed Bile is only released when cholecystokinin stimulates contraction of the gallbladder The hepatopancreatic sphincter opens when a peristaltic wave in the duodenal wall approaches it Bile salts break down fat into smaller droplets in a process called emulsification The lipases from the pancreatic juice then digest the small droplets Lack of bile salts causes poor lipid absorption and deficiency of vitamins A, D, E and K Figure 15.20 THE SMALL INTESTINE Extends from the pyloric sphincter to the beginning of the large intestine Receives secretions from the pancreas and liver plus completes digestion of chyme, absorbs products of digestion and transports residues to the large intestine Mesentery - double layered fold of peritoneal membrane that supports vessels and nerves Greater omentum - double fold of peritoneal membrane that drapes over the abdominal organs; can close off infections SMALL INTESTINE WALL Has intestinal villi that aid in absorption Blood capillaries and lacteals carry away absorbed nutrients Mucus-secreting goblet cells Watery fluid at the bases of the villi secrete bring nutrients into the villi Enzymes break down food before absorption takes place Peptidases, sucrase, maltase, lactase and intestinal lipase INTESTIAL LINING DEFICIENCIES Many adults do not have sufficient lactase to digest lactose or milk sugar AKA lactose intolerance Undigested lactose increases osmotic pressure of the intestinal contents and draws water into the intestines leading to diarrhea and gasses from bacteria digesting the undigested lactose Absorption of gluten may be impaired due to Celiac’s Disease binding of gluten triggers destruction of microvilli and leads to absorption deficiencies (malabsorption) ABSORPTION IN THE SMALL INTESTINE Carbohydrate digestion begins in the mouth with salivary amylase Enzymes from intestinal mucosa and pancreas finish off the carb digestion in the small intestine and villi absorb the monosaccharides Pepsin begins its digestion of proteins in the stomach and in the small intestine amino acids are absorbed Enzymes in the intestinal mucosa and pancreas digest triglycerides into fatty acids and glycerol that diffuse into villi STEPS INVOLVED IN FAT ABSORPTION THE LARGE INTESTINE At the end of the small intestine the ileocecal sphincter connects the ileum to the cecum of the large intestine The sphincter is constricted most of the time to prevent large intestine contents backing up to the ileum After a meal, a gastroileal reflex relaxes the sphincter forcing chyme into the cecum The large intestine consists of the cecum, colon, rectum and anal canal The appendix is a closed tube with a closed end projecting from the cecum Appendicitis - inflamed and infected appendix; if ruptures can cause peritoneal infection The colon is divided into four sections; ascending, transverse, descending and sigmoid THE ANUS The internal sphincter - smooth muscle under involuntary control The external sphincter - skeletal muscle under voluntary control Hemorrhoids enlarged and inflamed rectal vein branches that bulge out of the anus FUNCTIONS OF THE LARGE INTESTINE No digestion function Mucus is the only secretion in the large intestine Mucus protects the intestinal wall Mucus binds fecal matter and it’s alkalinity controls the pH of feces Absorbs water and electrolytes in the proximal region of the large intestine Houses bacteria that make vitamin K, B12, thiamine and riboflavin Mass movement waves move a large section of the intestinal wall that moves the contents toward the rectum after meals Feces = undigested materials, water, electrolytes, mucus, intestinal cells and bacteria Feces are 75% water and color is bile pigments while odor results from bacterial by-products NUTRITION AND NUTRIENTS Nutrients - carbohydrates, lipids, proteins, vitamins, minerals and water Macronutrients - carbohydrates, lipids and proteins - provide potential energy that can be expressed in calories - cellular oxidation results in 1 gram of carbohydrate or 1 gram of protein yielding 4 calories whereas, fat yields about 9 calories Micronutrients - vitamins and minerals MACRONUTRIENTS IN DETAIL CARBOHYDRATES - sugars and starches - Digestion breaks down complex carbs into monosaccharides for absorption -Cellulose is a complex carb that provides bulk facilitating movement of food in the digestive system CARBOHYDRATE UTILIZATION - the liver has enzymes that convert monosaccharides into glucose for cellular fuel -If foods do not supply sufficient carbs the liver will convert amino acids from proteins into glucose CARBOHYDRATE REQUIREMENTS - 125-175 grams daily to spare proteins from being broken down to avoid metabolic disorders resultin from excess fat utilization FAT DIGESTION Lipids - fats, oils, plant and animal sources -saturated fats - animal origin -Unsaturated -non-animal origin Beta oxidation is how lipids are used PROTEIN DIGESTION - 0.8 g/kg daily protein intake VITAMINS WATER SOLUBLE - VITAMIN C AND B VITAMINS -can be destroyed in cooking -B vitamins linked with energy due to their oxidating of carbs, proteins and fats -Vitamin C helps with iron absorption LIPID SOLUBLE - VITAMINS A, D, E AND K -can accumulate in adipose tissue - why excess amounts can be dangerous -not damaged with cooking MINERALS - calcium and phosphorous are the most abundant in the body -potassium, sulfur, sodium, chlorine and magnesium TRACE ELEMENTS - essential minerals found in small amounts - iron, manganese, copper, iodine, cobalt, zinc, fluoride, selenium and chromium DIETS Malnutrition - consequence of a diet lacking in essential nutrients The cause: lack of food or lack of quality of food The BMI - body mass index - is used to determine if one is underweight, adequate, overweight or obese. - to measure BMI one needs current weight and height measurements Figure 15.33 BMI CALCULATION CHART