The PRINCIPLE structure of the digestive system is the Alimentary Canal (Gastrointestinal Tract) = hollow tube much like a hallway in a home. I. Functions of the Digestive System a. Ingestion: Putting food in your mouth b. Breakdown of food: (mechanical and chemical) i. Fats Fatty acids + Glycerol ii. Polysaccharides Disaccharides iii. Proteins Amino Acids **You will be responsible for knowing an enzyme different than the enzymes discussed in class that digest each type of food, their action and where the enzyme is made** c. Peristalsis: food movement through system d. Absorption: taking in the nutrients into the bloodstream e. Defecation: elimination of indigestible food. f. Antibacterial: Destruction of bacteria g. Detoxification of harmful substances h. Storage II. Mouth (Oral cavity) a. Made up of the roof, floor and walls i. Roof is formed by hard and soft palates 1. hard palate formed by parts of the palatine and maxillary bones 2. soft palate located above the posterior portion of the mouth; consists mostly of muscle, Uvula found here initiates swallowing. 3. Uvula and soft palate prevent food or liquid from entering nasal cavities. 1
III. ii. Floor consists of tongue and muscles 1. tongue skeletal muscle covered with mucous membranes a. anchored to bones in skull and hyoid bone b. frenulum attaches to floor of mouth c. papillae raised surfaces on tongue where taste buds are located. b. Mouth is basic not acidic c. Tonsils disease fighter d. Salivary glands 3 per side; parotid, sublingual and submandibular i. These glands begins the digestion of starch ii. Saliva contains: 1. Mucus for lubrication of food 2. amylase enzyme for breakdown of starch 3. Antibodies keep mouth clean Teeth a. Numbers: kids = 20; adults = 32 (8 incisors, 4 canines, 8 pre-molars, 12 molars) b. Teeth are alive and covered with enamel for protection c. Types: i. Incisors sharp cutting edge used for mastication of food ii. Canines (aka cuspids) used to pierce of tear food iii. Pre-molars (aka bicuspids) large flat grinding surfaces with 2 cusps iv. Molars (aka tricuspids) large flat grinding surfaces with 3 cusps d. Typical tooth i. Crown 1. exposed/visible part of tooth 2. covered with enamel (hardest tissue in body) 3. dentin greatest proportion of the tooth shell 4. cementum anchoring tooth to jaw 5. pulp cavity center of tooth; filled with connective tissue, blood, lymphatic vessels and sensory nerves ii. Neck narrow portion surrounded by gingival (gum tissue); joins crown to root of tooth iii. Root fits into socket of jaw e. After food is chewed, it is called a bolus and then swallowed 2
IV. Pharynx connects mouth to esophagus; part of digestive and respiratory systems V. Esophagus a. Muscular mucous lined tube connecting pharynx to stomach (passageway for food) b. Approximately 25 cm long c. Epiglottis keeps food out of your trachea (windpipe); talking while eating is a bad idea! d. Peristalsis wavelike contractions that move food toward stomach e. Sphincter a muscle that opens and closes; located at both ends of esophagus VI. Stomach a. Very acidic ph = 2 high in HCl b. Responsible for both mechanical and chemical digestion of food c. Cardiac sphincter (end of esophagus) keeps food from reentering esophagus d. Main purpose is storage big meal = 4 hours; fatty meal = 6 hours e. Contraction of stomach mixes bolus with gastric juices to form chyme f. Presence of protein initiates the production of gastric juice i. Mucous ii. HCl iii. Pepsin (enzyme) begins protein digestion iv. Rennin (enzyme) digests milk proteins g. Most digestion in stomach occurs in the pyloric region. h. The only things absorbed directly through the stomach are alcohol and aspirin; the only food type to begin to be digested in the stomach are proteins i. Pyloric valve allows 3 ml of chyme through at a time; peristalsis of stomach forces chyme into digestive tract through the pyloric sphincter. 3
VII. Small Intestine a. Basic environment b. Approximately 7 m in length c. Begins at the pyloric sphincter and ends at the ileocecal sphincter. The main parts of the SI are the duodenum, jejunum and ileum d. Duodenum = < ½ meter (~ 1 ft); most digestion takes place here. Jejunum = 5 m; Ileum = 2ish m. e. Liver and pancreas add chemicals into the duodenum to help with digestion of food f. The SI is lined with intestinal glands (secretion) and plicae (circular folds) which are covered with villi (finger like projections that absorb nutrients) g. All digestion gets completed in the SI (refer to your enzyme chart in text) most carbs, 50% proteins and 100% fats VIII. Liver a. Fills entire upper right section of abdominal cavity; has ability to regenerate (even if you lose as much as 70%) b. If your liver stops functioning, you will die within 24 hours c. Liver is the largest gland in your body secretes bile which emulsifies fats and helps neutralize acids; fatty foods cause bile to be sent to the duodenum. d. The common hepatic duct drains bile out of the liver e. Liver will also help detoxify the body of harmful substances f. Liver makes cholesterol and blood proteins g. Liver stores excess sugar as glycogen and releases that sugar when needed. IX. Gallbladder a. Concentrates and stores bile b. If a gallstone blocks bile secretion, feces appears grey-white and jaundice occurs c. Jaundice occurs when the blood absorbs the excess bile. 4
X. Pancreas also part of endocrine system (insulin and glucagon) a. Lies behind stomach b. Secretes pancreatic juice and hormones into blood c. Pancreatic juice is the most important digestive juice it can digest all 3 major food types d. The pancreatic juice is basic (made up of sodium bicarbonate) so it neutralizes the stomach acid e. Most enzymes are produced in the pancreas; one eg is lipase = digests fats XI. Large Intestine a. Approximately 1.5 m long; aka colon b. Terminal portion of alimentary canal c. Purpose is absorption of water (drying out the indigestible food residue), absorbs vitamins and also some minerals d. No villi = not good for absorption of nutrients e. Normal passage of food through LI = 3 5 days i. Faster = diarrhea ii. Slower = constipation f. Made up of ascending, transverse, descending, sigmoid, rectum, anal canal, and anus g. Two sphincters at the anus i. Smooth muscle (involuntary) inner anal sphincter ii. Skeletal muscle (voluntary) outer anal sphincter XII. Appendix a. No important digestive function in humans b. May play a role in immune system XIII. Digestion a. Mechanical Digestion: breaks food into tiny particles Egs include: mastication, swallowing, peristalsis b. Chemical Digestion: Breaks food into nutrients body can use. Egs include: chemical reactions, enzyme action, secretions c. Carbohydrate digestion i. Little occurs in mouth (we chew too quickly) 5
ii. Gastric juice has no effect on carbohydrates iii. Intestinal and pancreatic juice breaks polysaccharide into smaller sugar molecules d. Protein digestion i. Starts in stomach ii. Rennin and pepsin break giant proteins molecules down a little iii. Intestinal enzymes break them down further into aa e. Fat digestion not much before intestine Explain the following terms: Diarrhea Heartburn Constipation Vomiting Pancreatitis Ulcers Gallstone Cirrhosis Jaundice Tongue tied Impacted tooth Cleft palate 6