The Digestive System

Life Science - Middle School

The Digestive System © C opyright NewPath Learning. All Rights Reserved. 94-4902 Mouth Mechanical digestion begins in the mouth where the teeth grind food into smaller pieces. The tongue mixes the food with saliva. Saliva moistens the food and begins the process of chemical digestion which breaks down starch into simple sugars. Esophagus The esophagus is a tube of muscle that connects the mouth to the stomach. The esophagus is lined with smooth muscle, which contracts in a wavelike motion forcing food to move down the esophagus in a process called peristalsis. Digestive Organs Peristalsis blood vessels small intestine villi capillaries lumen liver stomach pancreas digestive juices small intestine gall bladder Digestion is a process of breaking down different nutrients into molecules that the body can use. There are three main functions of the digestive system: 1. Breaks down foods into molecules that the body can use. 2. Absorbs the molecules into the blood and sends them throughout the body. 3. Eliminates waste from the body. Stomach After the esophagus, food enters the stomach. The stomach is made up of muscle which contracts, churning the food inside. This is a type of mechanical digestion. The stomach also produces digestive juices that coat the food and digests it chemically. The digestive juice contains an enzyme called pepsin which breaks down proteins into amino acids. Small intestine The majority of chemical digestion and absorption takes place in the small intestine. The chemicals and enzymes that are necessary for chemical digestion are produced by the small intestine, pancreas, and the liver. The pancreas produces enzymes that aid in the break down of fats, proteins, and starches. The liver produces bile, a chemical that breaks up fatty substances. After the liver produces bile, it stores it in a structure called the gallbladder. The inner lining of the small intestine has a layer of structures called villi which increase the surface area and allow nutrients to pass into the blood stream. Large intestine The large intestine is the last section of the digestive system and receives food that cannot be absorbed into the blood stream. While little digestion takes place here, the large intestine absorbs water from undigested food and stores solid wastes until they leave the body. The bacteria that’s present supplies the body with vitamin K. absorption (mostly small intestine) ingestion propulsion defecation mechanical digestion (chewing) (churning) (peristalsis) mechanical digestion chemical digestion Digestive Process rectum large intestine small intestine stomach pancreas liver tongue salivary glands esophagus food
\|xiBAHBDy01779qzZ © C opyright NewPath Learning. All Rights Reserved. 94-4902 The Digestive System Digestive Organs capillaries pancreas digestive juices salivary glands esophagus small intestine gall bladder stomach large intestine teeth liver tongue lumen rectum mouth villi Key Vocabulary Terms Digestive Process What are the three main functions of the digestive system? 1. __________________________________________________________________ 2. __________________________________________________________________ 3. __________________________________________________________________ Describe the function of each of the following structures: Mouth ______________________________________________ _________________________________________________ Esophagus __________________________________________ _________________________________________________ Stomach ____________________________________________ _________________________________________________ Small intestine _______________________________________ _________________________________________________ Large intestine _____________________________________ ______________________________________________