Digestive System Ridgewood High School

NUTRITION O the life activities by which organisms obtain and process nutrients for energy, growth, repair, and regulation. O humans are heterotrophs--they have to get there food from somewhere, they cannot make their own O humans need food; which can be described as either nutrients or roughage O carbohydrates, lipids, proteins, vitamins, minerals, and water* complex carbs O carbs, lipids, and proteins MUST be digested; vitamins, minerals, and water can be absorbed without digestion O complex carbs that cannot be broken down but is necessary for the digestive system to work; also known as fiber

Human Digestive System 1) taking in food--ingestion 2) breaking it down mechanically and chemically (hydrolysis)--digestion 3) absorbing the nutrients in food OR 4) egesting the parts of your food which is indigestible-- egestion O the human digestive system (also called the alimentary canal) is a one-way gastrointestinal (gastro=stomach) tract with 2 openings O * food is moved in the correct direction by slow muscle contractions called peristalsis

STRUCTURES OF THE HUMAN DIGESTIVE SYSTEM

Oral Cavity O ingestion of food occurs here; contains teeth, tongue, and openings of the salivary glands O A) teeth-- O used to break down food mechanically (mechanical digestion) to increase surface area for digestive enzymes (chemical digestion) O B) tongue-- O moves food around mouth so that teeth work more effectively, helps mix food with saliva, and moves food to the back of the mouth for swallowing O C) salivary glands-- O secretes saliva into digestive system which contains the hydrolytic (the breakdown with water--digestive) enzyme AMYLASE, which digests starch *chemical digestion of carbohydrates begins in the mouth

Esophagus O when you swallow, food goes into this small tube (about 10 inches--25 centimeters--long) O mucus is secreted to lubricate the food to slide easier O peristaltic action (peristalsis) moves the food towards the stomach O A) epiglottis O when you swallow, a small flap of tissue closes off your windpipe (trachea) so that food will not go down into the lungs * this momentarily stops breathing!

Stomach-- O a thick-walled, muscular sac (organ) whose main job is to liquefy and further digest food O the lining of the stomach contains gastric glands which secrete gastric juices which contain: O a) gastric protease b) hydrochloric (HCl) acid c) mucus d) water O gastric protease is an enzyme which begins the digestion of proteins O the hydrochloric acid lowers the pH of the stomach, not to break down food, but to provide the optimum (best) pH for the gastric protease to work! O the mucus protects the stomach walls from being eaten away O the water is used for chemical digestion (hydrolysis) O the stomach also stores the food for a while; liquids can pass through the stomach in 20 minutes or less while solids can remain in the stomach for 2-6 hours.

BOTH MECHANICAL AND CHEMICAL DIGESTION OCCUR IN THE STOMACH! O stomach walls churn food up (MECHANICAL) O hydrolytic enzymes digest food (CHEMICAL)

Small intestine O partially digested food then enters the small intestine O it is a long tube (just over 20 feet--6.5 meters--long in an average human) where a major portion of food is digested O intestinal glands line the intestinal walls and secrete lipase, intestinal protease, and maltase to complete chemical digestion of food O food is digested with the help of accessory organs (food never goes to these places to be digested)

Small Intestine cont… O A) liver-- O * produces bile and sends it to the gall bladder * bile is not an enzyme; however it does break down big globs of fat to smaller globblets--called EMULSIFICATION O B) gall bladder-- slowly secretes bile into the small intestine O C) pancreas-- secretes enzymes into the small intestine such as intestinal amylase, lipase, and intestinal protease

Large Intestine O takes the undigested food and absorbs most of the water and any vitamins not yet absorbed O solidifies the liquid wastes into solid feces (includes undigested and indigestible material--roughage--bacteria, bile, mucus, and worn out cells from the digestive tract) * strong peristaltic action forces feces out the anus O A) rectum-- where solid wastes are temporarily stored O B) appendix-- has no known function, however, an inflammation of this organ (appendicitis) can be life threatening if it ruptures O C) anus-- opening in the human body through which feces (solid wastes) are removed

ABSORPTION OF DIGESTED MATERIAL O food is absorbed by the body in the small intestine, after it has been digested O the intestinal wall is lined with millions of villi which increase the surface area for absorption O in each individual villi (shown below), there are capillaries (very small blood vessels) and other small ducts (pipes) of the lymphatic system called lacteals