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Unit 4 – part 1 •We eat about 500kg of food per year. •We make approximately 1.7 liters of saliva every day. •Every day 11.5 liters of digested food, liquids and digestive juices flow through the digestive system, but only 100 mL is lost in feces. •Digestive problems cost Americans $50 billion each year in both direct costs and absence from work. •By age 50, many people will produce only 15% of the Hydrochloric Acid (stomach acid) they released at age 25. •Most of us pass somewhere between 200 and 2,000 ml of gas per day (average, about 600 ml) in roughly 13-14 passages. •How big is your stomach ? An adult’s stomach holds about 1 liter of food. A child’s stomach holds a little bit less. Your stomach gets bigger the more you eat. A large adult can eat and drink up to 4 liters of food and liquid at one meal! •How long are the intestines ? The small intestine is more than three times as long as the whole body ! In an adult, this is about 21 feet long. The large intestine is another 5 feet long. The whole tube from the mouth to the anus is about 30 feet long. Wow ! •As a group, vegetarians produce more gas than meat-eaters because the intestinal enzymes can't digest the cellulose in vegetables' cell walls Functions of the Digestive System • Ingest food • Secretes (enzymes, bile, HCl) to assist in digestion • Digests macromolecules • Absorbs food •to make energy •to help us grow and repair ourselves • Eliminates indigestible waste Four Steps of Digestion 1. 2. 3. 4. Ingestion of food in mouth Mechanical & Chemical digestion Absorption of molecules Elimination of indigestible substances PATHWAY Mouth ->Pharynx>Esophagus->Stomach-> Small Intestine->Large Intestine-> Rectum->Anus 3 Accessory Organs Assist in digestive process Liver, Gall Bladder Pancreas Mechanical digestion – Large piece of food become smaller ones without creating a new product – Examples: • Chewing of food in the mouth • Churning and mixing of food in the stomach Chemical digestion – Enzymes chemically break down macromolecules into smaller products that can be absorbed – Example: polymer → monomer Functions: 1. Ingestion 2. To begin digestion: a) mechanical b) chemical 1) Teeth • Begins mechanical digestion to increase SA of food for enzymes to act 2) Salivary Glands: produce saliva, which: a) Liquifies food b) chemically digests - contains salivary amylase (optimal pH 7) c) Lubricates and softens the BOLUS (saliva + chewed food). d) Enzymes that kill bacteria Starch SALIVARY AMYLASE maltose 3) Tongue (a muscle): a. Contains taste buds b. Moves the food c. Pushes the BOLUS to the back of the throat to the ‘swallow reflex center’. Structure: region at the back of the throat. Function: Swallowing: When food is placed on the ‘reflex center’, the following things happen: a) the soft palate covers nasopharynx b) the epiglottis covers the trachea (respiratory) c) peristalsis of the esophagus begins A flap of tissue that covers the trachea when we swallow food and liquid •Long muscular tube •No digestion occurs here •that connects to stomach via the cardiac sphincter (ring of muscle which stops acidic chyme from reentering the esophagus) Dissected esophagus – notice the thick, ribbed lining of the tract. BOLUS moves through the esophagus by PERISTALSIS (a slow, rhythmic contraction) Peristalsis continues down the length of the entire digestive tract. Structure: • thick walled, ‘J’ shaped organ Functions: 1) churns & mixes food (mechanical digestion) •aided by the ridges or rugae in the stomach layer 2) Stores food & releases slowly to small intestine 3) Makes gastric juice – secreted by gastric glands (chemical digestion) RUGAE Gastric Juices contain: 1. water (solvent) 2. Pepsinogen (protein digestion) 3. Hydrochloric Acid (strong acid) 4. Mucous HCl released when proteins enters •creates pH of 2.5 - kills bacteria & denatures salivary amylase • transforms pepsinogen (inactive) to PEPSIN (active enzyme) HYDROCHLORIC ACID PEPSIN •Pepsin hydrolyses proteins into smaller called peptides chains for aa Pepsinogen Protein PEPSIN peptides Mucous secretions protect stomach cells from HCl • An ULCER can result if acid penetrates the mucous layer Bolus leaves the stomach as an acidic liquid called CHYME. pyloric sphincter, at the base of the stomach, will release the chyme into small intestine at a slow, controlled rate. 3 regions: 1. Duodenum: 2. Jejenum: The rest of chemical digestion 3. Ileum: absorbs nutrients into BLOOD & LYMPH •increased rate of absorption •the highly folded walls creating a very large surface area. • folds in layer of small intestine called VILLI. • villi also have smaller folds called MICROVILLI. • Villi contains: – Blood capillaries absorb glucose, aa and nucleotide components – Lacteals (lymph capillaries) absorb glycerol & fatty acids Chemical Digestion – from pancreatic and intestinal juice Physcial Digestion – with assistance from gallbladder • Small intestine connected to 2 accessory organs 1) Pancreas 2) Gallbladder The pancreas is a dual organ a) ENDOCRINE GLAND which makes hormones insulin and glucagon. b) EXOCRINE GLAND which make the enzymes to digest carbs, fats, proteins and nucleic acids. high blood sugar → insulin secreted • insulin removes glucose from the blood which: 1. causes the liver to store it as glycogen 2. promotes formation of fats 3. causes cells to absorb glucose low blood sugar → glucagon secreted • glucagon causes the liver to break down glycogen and release glucose into the blood Diabetes Type 1 (juvenile onset) Type 2 (adult onset) • Deficiency in insulin • Not enough insulin or enough but a problem with insulin receptors on cell membranes •Results in high blood glucose levels •Controlled with diet SALT + N (memory trick): 1. Sodium Bicarbonate - neutralizes acidic chyme; changes pH to 8.5 (basic) 2.Pancreatic Amylase - an enzyme that converts starch to maltose. 3.Lipase - enzyme that converts lipids into fatty acids and glycerol 4. Trypsin - an enzyme that converts proteins into peptides. 5. Nucleases - enzymes that convert nucleic acids (DNA and RNA) into nucleotides. …and of course, water to hydrolyze these reactions • Connected to Liver and small intestine • Function – store & send BILE to SI via bile duct • BILE is NOT an enzyme • Helps in physical digestion of LIPIDS • Breaks LIPIDS into smaller particles this is called EMULSIFICATION • Bile is made by liver •largest internal organ. •blood from the villi travels via the hepatic portal vein to the liver. •liver acts as a ‘gatekeeper’ to the blood by keeping levels of various nutrients in the blood constant. Hepatic Portal System • Absorbed nutrients (from small intestine) are taken to liver via hepatic portal vein. • Liver stores excess glucose and glycogen, releasing it as needed. Liver – 6 functions – KNOW!!! B.B.B.B.B.U. 1. 2. 3. 4. 5. 6. Blood Sugar -regulates through insulin & glucagon Blood detoxify – e.g. turns alcohol into fatty acids Bile produce Blood proteins produce – e.g. albumin, fibrinogen Blood Cells red break down Urea – produce Regulates the blood glucose level High blood sugar Glucose INSULIN Glycogen Low blood sugar Glycogen GLUCAGON Glucose Urea production If necessary the liver can convert amino acids into glucose to maintain glucose concentration of plasma. • this process produces urea • removed by the kidneys in the production of urine. Cells of small intestine (duodenum) make and secrete intestinal juices that will finish chemical digestion 1. Peptidases digest peptides into a.a.’s 2. Nucleosidases digest nucleotides into sugar, phosphate & N-base 3. Maltase digests the maltose into 2 glucose molecules Villi are finger-like projections that cover the lining of the sm. Intestine •Increases SA & absorption rate Capillaries of the villi absorb sugars, amino acids, & nucleotides Lacteals of the villi absorb glycerol & fatty acids and transfer to lymph. Junction of Small and Large Intestine Appendix • Has lymph tissue to help fight infection • Subject to inflammation = appendicitis • May be removed large in diameter, but short (1.5 m long) in length It consists of: 1. colon 2. rectum 3. anus Absorption of the water and salts And receives & stores undigestible wastes & fibres • has anaerobic bacteria, E.Coli , that: 1. eat the wastes and produce useful things that we need to survive (ie: vitamin K and amino acids) 2.produce growth factors (proteins that stimulate cell growth) 3. Produce waste of their own (methane gas) Phew! At the end of the large intestine, wastes are transformed into pasty ‘feces’ which build up in rectum until message is sent to central nervous system to stimulate bowel movement The entire process of digestion from the mouth to the anus lasts 24 hours. • Sphincter muscle through which feces exits the body If feces moves through too slowly: • Too much water is absorbed. • feces become hard and you are constipated. THE END...GET IT... “THE END”