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Ch 15 Notes DIGESTIVE SYSTEM AND NUTRITION DIGESTION Digestion – breakdown of foods and the absorption of the resulting nutrients. Two kinds Mechanical – breaks large pieces into smaller ones without chemically alteration. (chewing) Chemical – breaks food into simpler chemicals (enzymes) DIGESTIVE SYSTEM COMPOSITION Alimentary canal From mouth to anus Secretes substances used in digestion Organs – mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus Accessory organs – salivary glands, liver, gallbladder, pancreas Surface area – 186 square meters STRUCTURE OF ALIMENTARY CANAL Mucosa – Innermost Layer epithelium, connective tissue, and some smooth muscle lumen – folds that increase surface area tubular glands that secrete mucous STRUCTURE OF ALIMENTARY CANAL Submucosa loose connective tissue glands, blood vessels, lymphatic tissue, nerves Nourishes surrounding tissues and carries away absorbed materials STRUCTURE OF ALIMENTARY CANAL Muscular Layer Two coats of smooth muscle Inner coat – circular fibers that decrease diameter Outer coat – longitudinal fibers that shorten the tube STRUCTURE OF ALIMENTARY CANAL Serosa/Serous Layer – Outermost layer Outside epithelium and connective tissue Also called visceral peritoneum Lubricates outer tube to reduce friction between surfaces in the abdominopelvic region FIG 15.3 MOTOR FUNCTIONS OF ALIMENTARY CANAL Mixing Rhythmic contraction of smooth muscles mixes content with gastric juices Stomach and small intestine Contents move in many directions at one time MOTOR FUNCTIONS OF ALIMENTARY CANAL Moving (Propelling) Peristalsis – wavelike motion of smooth muscle As wave moves, contents are pushed ahead of it Only moves in one direction FUNCTIONS OF ORGANS Fill out the table with the functions of each organ in the digestive system. We will do the enzyme part later. Organ Functions Table TEETH Function: Begin mechanical digestion Types Incisors (8) – bite off pieces of food Canine (4) – grasp and tear food Bicuspid (8) – grind food particles Molar (12) – grind food particles Two main parts Crown Root STRUCTURE OF TEETH - CROWN Crown is covered by enamel Dentin – harder than bone Pulp – blood vessels, nerves, connective tissue STRUCTURE OF TEETH - ROOT Root is covered by cementum – thin, bonelike layer Periodontal ligament – blood vessels and nerves, attaches tooth to jaw SALIVARY GLANDS Secrete saliva – dissolves food; begins chemical digestion Two types of secretory cells: serous and mucous Serous – salivary amylase splits starch and glycogen into disaccharides (for carbohydrate digestion) Mucous – coats food for swallowing Why is it difficult to swallow something that tastes nasty? MAJOR SALIVARY GLANDS Parotid glands – in front of the ear Largest Rich in salivary amylase Submandibular – floor of mouth, near lower jaw Equally serous and mucous Sublingual – under the tongue Primarily mucous PHARYNX No digestion – just a passageway Pharynx – only oropharynx and laryngopharynx are for food SWALLOWING Three stages Voluntary Tongue rolls food into bolus and pushes it into oropharynx SWALLOWING Involuntary Soft palate raises, epiglottis closes off larynx, tongue presses soft palate Longitudinal muscles in pharyngeal wall pull the pharynx upward Esophagus opens Peristalsis pushes food downward SWALLOWING During steps 1 and 2, breathing momentarily ceases Involuntary – Peristalsis pushes food from esophagus to the stomach. ESOPHAGUS ~25 cm long Penetrates the diaphragm through the esophageal hiatus Mucous glands throughout to lubricate food Lower espohageal sphincter – closes entrance to stomach so contents don’t come back into the espophagus STOMACH Receives food from esophagus Mixes with gastric juices Rugae – gastric folds Starts protein digestion Limited absorption Small amounts of water, salts, alcohol Moves food to small intestine STOMACH - STRUCTURE Cardia – area near esophogeal opening Fundus – balloons inferior to cardia; temporary storage area Body region – main part of the stomach Pylorus – Area that tapers to the duodenum Pyloric canal – approaches the small intestine Pyloric sphincter – muscle valve that controls gastric emptying STOMACH - SECRETIONS Gastric glands – have gastric pits at the end. Mucous cells – secrete thick mucous to prevent the stomach from digesting itself Chief cells – secrete enzymes Parietal cells – secrete hydrochloric acid Intrinsic factor – helps small intestine absorb Vitamin B12. STOMACH – ENZYME Pepsinogen + HCl -> pepsin Starts the digestion of protein GASTRIC SECRETION REGULATION Secretion is regulated by both the brain and by hormoes Stomach – gastrin Small intestine - cholecystokinin When you see, smell, or taste food, your stomach begins releasing gastric juices. As food moves into the intestine, gastric juice secretion is inhibited STOMACH ACTIONS Mixing creates a semifluid paste called chyme. When chyme reaches the pylorus, it relaxes the pyloric sphincter, pushing it into the small intestine STOMACH ACTIONS Food content determines time Liquids – fastest Carbs – very fast Proteins – a little slower Lipids – very slow PANCREAS Pancreas has both endocrine and exocrine qualities. Secretes digestive fluids called pancreatic juices. PANCREAS STRUCTURE Located behind the stomach, with its head in the c-shaped curve of the duodenum and its tail against the spleen PANCREAS STRUCTURE Mostly made up of pancreatic acinar cells that produce pancreatic juices These lead into a pancreatic duct, which carries juices to the duodenum. Coincides with the bile duct from the gall bladder. Hepatopancreatic sphincter controls release. PANCREATIC JUICE - ENZYMES Pancreatic amylase – breaks down carbs Pancreatic lipase – breaks down lipids Nucleases – breaks down nucleic acids Trypsin, chymotrypsin, carboxypeptidase – break down proteins Several are necessary because no one enzyme can break all peptide bonds. Cannot be activated until they come into contact with other enzymes (i.e. – enterokinase, cholecytokinin) PANCREATIC SECRETION - REGULATION Controlled by nervous and endocrine systems When chyme reaches the duodenum, the hormone secretin is released, which stimulate the release of pancreatic juice into the duodenum. Pancreatic juice, high in bicarbonate ions, neurtalizes the acid in the chyme to provide a more favorable environment in the intestine LIVER Location – Upper right quadrant just under the diaphragm Well supplied with blood vessels Heaviest organ – weighs about 3 lbs LIVER Enclosed by fibrous capsule and split into the left and right lobes by connective tissue. Lobes are subdivided into hepatic lobules – hepatic cells radiating from a central vein. LIVER - STRUCTURE Blood from digestive tract’s hepatic portal vein bring absorbed nutrients in In the hepatic sinusoids, there are large phagocytic macrophages called Kupffer cells. They remove bacteria and other foreign particles that enter through hepatic portal vein Hepatic cell secretions -> bile canuliculi -> bile ductules -> hepatic ducts ->common hepatic duct LIVER - FUNCTIONS Carbohydrate metabolism – controlled by hormones insulin and glucagon which can lower or raise blood glucose levels Lipid metabolism – breaks down, synthesizes cholesterol, converts sugars to fats for storage Protein metabolism – forms urea, makes plasma proteins (clotting factors), changes amino acids into other amino acids LIVER - FUNCTIONS Storage – Vitamins A, D, B12, and iron Protection – destroy defective red blood cells, phagocytize foreign substances and toxins (i.e. – alcohol) Secretes bile BILE Yellowish-green liquid secreted by hepatic cells Contains – water, bile salts, bile pigments (i.e. biliruben), cholesterol, and electrolytes Bile salts are the only substances that have digestive function. They break fat molecules into much smaller droplets (emulsification) so they can more easily be digested Also help with absorption of vitamins A, D, E, and K. GALLBLADDER Pear-shaped sac connected to the cystic duct and to the hapatic duct. Epithelium lined with strong muscles Stores bile, absorbs water, releases bile into small intestine GALLBLADDER AND LIVER CONVERGE Common hepatic duct and cystic duct join to form the bile duct. Bile duct empties into small intestine. Controlled by hepatopancreatic sphincter. RELEASE OF BILE Bile is released when the hormone cholocytokinin relaxes the hepatopancreatic sphincter. It is released along with the pancreatic juices. SMALL INTESTINE Tubular organ that goes from pyloric sphincter (stomach) to the large intestine. Receives secretions from the pancreas and liver, completes digestion of chyme, absorbs products of digestion, transports residues to large intestine. SMALL INTESTINE – PARTS Doudenum Jejunum (2/5) – bigger in diameter, more active Ileum (3/5) Connected to posterior abdominal wall by the mesentery Blood vessels, nerve and lymphatic tissue, Ileocecal Sphincter INSIDE THE SMALL INTESTINE LINING Intestinal villi line the inside of the mucosa. Increase surface area Aid in absorption Lymph vessel (lacteal) and blood vessels inside, which carry away absorbed nutrients. Nervous Tissue SMALL INTESTINE ENZYMES Peptidase – Breaks down peptides (proteins) into amino acids Sucrase, maltase, lactase – Breaks down disaccharides into monosaccharides Instestinal Lipase – Breaks down fats into fatty acids and glycerols REGULATION OF SECRETION Chyme offers both mechanical and chemical stimulation in the duodenum and along the intestinal wall. ABSORPTION – SMALL INTESTINE Small intestine is the most important absorption organ on the alimentary canal. Very little absorbable material reaches the large intestine. Carbs – Easily absorbed into blood capillaries by facilitated diffusion or active transport. ABSORPTION – SMALL INTESTINE Amino acids (from proteins) – absorbed into the blood. Fats – Broken down, reassembled, covered in protein coat (chylomicrons), absorbed by lymph vessels, which then take it to blood vessels Also absorbs – electrolytes and water MOVEMENTS OF THE SMALL INTESTINE Mixing – segmentation mixes the contents and “swishes” them back and forth. Moving – peristalsis over 3 to 10 hours If contents move too quickly, water and electrolytes that would normally be absorbed are not. This causes diarrhea. LARGE INTESTINE Has a larger diameter than small intestine. Four main parts: cecum, colon, rectum, anal canal Absorbs water and electrolytes from chyme. Forms and stores feces. PARTS Cecum – Connection to ileum Appendix – lymphatic; no known digestive function PARTS Colon Ascending Transverse Descending Sigmoid Rectum PARTS Anal canal Anus Two sphincter muscles: internal anal sphincter muscle and external anal sphincter muscle Skeletal muscle – voluntary control LARGE INTESTINAL WALL Lacks villi Longitudinal muscle fibers form 3 distinct bands FUNCTIONS Little to no actual digestive properties. Mucous is the large intestine’s only major secretion. Will absorb water and electrolytes in the first half. Substances that remain become feces and are stored in the second half. FUNCTIONS – INTESTINAL BACTERIA Bacteria that live in colon (intestinal flora) can break down some materials that are still useful to it at this point. (i.e. cellulose) They make Vitamins K, B12, thiamine, and riboflavin They may also make intestinal gas MOVEMENTS OF LARGE INTESTINE Mixing and moving like small intestine, but slower. Waves happen only 2-3 times a day. Typically mass movements follow a meal – gastrocolic reflex Voluntary – defecation reflex Internal and external anal sphincters relax FECES Material not absorbed during digestion, water, electrolytes, mucus, shed intestinal cells, bacteria Pigmentation and odor are due to bacterial action