THE DIGESTIVE SYSTEM LESSON PLAN INTRODUCTION *** read digestive story (approximately 5 minutes) Ask Students: What is the purpose of the digestive system? Answer: to break down food into units that can be absorbed and used by the body. Points to include in discussion: Food gives fuel that allows us to move, think, and breathe. The amount of calories that a body uses each day varies depending on the person’s size, weight, body build, occupation, and age. Ask Students: Why does food need to be broken down? Answer: Food is a fuel source for the body that cannot be used by the body until it is broken down Points to include in discussion: Basic components of food are proteins, sugars, fats, vitamins, minerals, and water. These components are further broken down into fundamental building blocks. Carbohydrates such as starch are broken down into simple sugars such as glucose. Fats are broken down into fatty acids and glycerol. Sugars and fats are used for energy Fats are used for insulation Proteins, vitamins, and minerals are used to build the structure of our body such as the skeleton and skin. DISCUSSION THE MOUTH Ask students: Where do you think the process of digestion begins? Answer: in the mouth Ask students: What does the mouth do to aid in digestion? Answer: Points to include in discussion: The purpose of the mouth is to initiate digestion Chewing causes the mechanical (physical) breakdown of food Saliva causes the chemical breakdown of food through a chemical substance or enzyme called ptyalin Saliva is a liquid produced in the salivary glands found in the lining of the cheeks There are three pairs of salivary glands located in the front of the mouth below the tip of the tongue, beneath the tongue, and in front of the ears. Saliva helps digestion by adding water and enzymes which serve to break down some of the components of food. Saliva helps in swallowing by lubricating food and by holding it together Teeth assist in breaking down food by cutting, tearing, and grinding. A bolus is the ball of food and saliva that is shaped by the tongue during chewing A bolus is the end product of chewing ***demonstrate model (pour colored water into mouth) THE ESOPHAGUS Ask students: Where does food go when it leaves the mouth? Answer: the esophagus Points to include in discussion: The esophagus is the 25 cm (10”) long muscular tube that connects the mouth with the stomach The esophagus is a separate tube from the windpipe (trachea), but the two do meet in the lower pharynx A small flap of tissue called the epiglottis automatically closes over your windpipe when you swallow to keep food from entering the windpipe It takes food about seven seconds to travel through the esophagus Ask students: Can we swallow if we were upside down or in outer space? Answer: yes Points for discussion: Food travels down the esophagus because of peristalsis, a wavelike contraction of muscles in the esophagus Peristalsis is so strong, that it can force good through parts of your digestive system when you are lying down, standing on your head, or floating upside down in the weightlessness of outer space THE STOMACH (CHEMICAL BREAKDOWN) Ask students: Where does the food go when it leaves the esophagus? Answer: the stomach Points to include in discussion: The stomach continues the breakdown of food The stomach contains dilute hydrochloric acid and pepsin A thick mucus coat or lining protects the stomach from the harmful acids it contains Pepsin is an enzyme in the stomach that breaks proteins into its building blocks— amino acids. The stomach physically breaks down food with its strong muscular walls by compressing and churning the food To keep the food in the stomach, sphincter valves are used to keep the stomach closed The sphincter valves need to keep the acid-food mixture in the stomach so it cannot escape back into the esophagus. The esophagus does not have the same coating to protect it from the acids that are in the stomach Heartburn is caused by acid partially traveling up the esophagus Ulcers are caused when there is a hole in the stomach lining The stomach regenerates its lining every three days When the food has been processed by the stomach it is called chyme. ***Remind students that the stomach also does mechanical and/or physical breakdown of food as well. THE SMALL INTESTINE ***Remind students that the food in the stomach is now called chyme Ask students: Where does the chyme go when it leaves the stomach? Answer: the small intestine Points to include in discussion: When the food has been processed by the stomach into chyme, a sphincter between the stomach and the small intestine opens. Peristalsis pushes the food into the small intestine. The small intestine is 2.5cm thick and over 6m (18’) long. Food moves through the small intestine by peristalsis Most of digestion takes place in the small intestine The walls of the small intestine releases an intestinal juice that contains several types of digestive enzymes that breaks the food into small units that can be absorbed by the cells in the small intestine Food does not go through the liver and the pancreas, but these argans send juices to the small intestine that assist in digestion After 3-5 hours, most of the food in the small intestine is digested The small intestine is the first area of absorption—the first place where nutrients are absorbed from the food The small intestine has an inner lining that looks like wet velvet The inner lining of the small intestine is covered with millions of tiny fingerlike structures called villi Digested food is absorbed through the villi into a network of blood vessels that carry the nutrients to all parts of the body By the time the food is ready to leave the small intestine, it is basically free of nutrients except water. What remains are undigested substances that include water and cellulose (a part of fruits and vegetables). ***demonstrate length of intestines LARGE INTESTINE Ask students: Where does the chyme go when it leaves the small intestine? Answer: the large intestine Points to include in discussion: The large intestine is the final area of absorption in the digestive system The large intestine is shaped like a horseshoe that fits over the coils of the small intestine The large intestine is about 6.5cm in diameter but only about 1.5 m long After spending about 18 – 24 hours in the large intestine, most of the water in the undigested food is absorbed Materials not absorbed form a solid waste ***demonstrate model REVIEW Use flashcards and allow students to call out answers.