The Digestive System (2:27) Click here to launch video Click here to download print activity

The digestive system provides nutrients and energy for your body through the digestion of food.

mastication peristalsis gastric juices bile peptic ulcer appendicitis

What Happens During Digestion In digestion, foods are broken down and absorbed as nourishment or eliminated as waste. The foods you eat must be broken down into nutrients to be absorbed into the blood and carried to the body’s cells.

What Happens During Digestion Digestion The mechanical and chemical breakdown of foods within the stomach and intestines for use by the body’s cells. Absorption The passage of digested food from the digestive tract into the cardiovascular system. Elimination The body’s expulsion of undigested food or body wastes. Three Main Processes of the Digestive System

How Digestion Works The digestive system consists of the mouth, esophagus, stomach, and intestines. Carbohydrates begin digesting in the mouth, protein begins digesting in the stomach, and fats begin digesting in the small intestines.

How Digestion Works Mechanical Processes Chewing, mashing, and breaking food down. Digestion includes two processes. Chemical Processes Secretions produced by digestive organs.

How Digestion Works The teeth break the food you eat into smaller pieces. Mastication prepares food to be swallowed. Mastication The process of chewing

How Digestion Works Salivary glands produce saliva, which contains an enzyme that begins to break down the starches and sugars in food into smaller particles. The tongue prepares chewed food for swallowing by shaping it.

The Esophagus When food is swallowed, it moves through the esophagus, stomach, and intestine through peristalsis. Peristalsis A series of involuntary muscle contractions that moves food through the digestive tract

The Stomach The stomach has three tasks: Mixing foods with gastric juices Storing partially digested food and liquid Moving food into the small intestine

The Stomach The hydrochloric acid in gastric juices kills bacteria taken in with food and creates an acidic environment for pepsin to do its work. Gastric juices Secretions from the stomach lining that contain hydrochloric acid and pepsin, an enzyme that digests protein

The Stomach The stomach holds the food for further digestion before it is moved into the small intestine. As food is digested in the stomach, it is converted to chyme, a creamy, fluid mixture of food and gastric juices, which is moved into the small intestine.

The Stomach The three layers of stomach muscles each move in different directions to aid both mechanical and chemical digestion.

The Stomach

The Pancreas, Liver, and Gallbladder The liver produces bile and the pancreas produces other enzymes that break down the carbohydrates, fats, and proteins in food in the small intestine. Bile A yellow-green, bitter fluid important in the breakdown and absorption of fats

The Small and Large Intestines The small intestine is 20 to 23 feet in length and 1 inch in diameter. It consists of three parts: the duodenum, the jejunum, and the ileum.

The Small and Large Intestines About 90 percent of all nutrients are absorbed through the small intestine. Unabsorbed material leaves the small intestine in the form of liquid and fiber and moves by peristalsis into the large intestine.

The Small and Large Intestines The inner wall of the small intestine contains millions of fingerlike projections called villi that are lined with capillaries that absorb the nutrients.

The Small and Large Intestines The undigested parts of the food—fiber, or roughage—pass into the colon, or large intestine. Its function is to absorb water, vitamins, and salts, and to eliminate waste.

Digestive System Problems Digestive problems range from indigestion to acute conditions that require immediate medical attention. Taking care of your digestive system begins with the foods you eat and how you eat them.

Digestive System Problems Eat slowly and chew your food thoroughly. Wash your hands before preparing or eating meals. Eat a variety of low-fat, high-fiber foods. Tips for Maintaining Digestive Health Drink at least eight 8-ounce glasses of water a day. Avoid using food as a way of dealing with your emotions.

Functional Problems Indigestion Constipation Heartburn Gas Nausea Diarrhea Discomfort in the abdomen, sometimes with gas and nausea. Feces become dry and hard, making bowel movements difficult. A burning sensation in the chest that may rise up to the throat. Cramps or an uncomfortable feeling of fullness in the abdomen. A feeling of discomfort that sometimes precedes vomiting. The frequent passage of watery feces.

Structural Problems Tooth decay Gastritis Gallstones Lactose Intolerance Colitis Makes it difficult to chew foods thoroughly. Inflammation of the mucous membrane that lines the stomach Blockage of the bile duct between the gallbladder and the small intestine. An inability to digest lactose, a type of sugar found in milk and other dairy products. Inflammation of the large intestine, or colon.

Structural Problems Colon cancer Hemorrhoids Crohn’s Disease Cirrhosis Cancer that usually develops in the lowest part of the colon, near the rectum. Veins in the rectum and anus that may become swollen and inflamed. Inflammation of the lining of the digestive tract. Scarring of the liver tissue caused by prolonged heavy alcohol use.

Structural Problems Appendicitis can cause the appendix to burst, spreading infection throughout the abdomen, which can lead to death. Appendicitis Inflammation of the appendix

Structural Problems Peptic ulcers can be caused by a bacterial infection or the overuse of aspirin. They can cause stomach bleeding. Peptic ulcer A sore in the lining of the digestive tract

Structural Problems Cirrhosis is caused by prolonged heavy alcohol use. It can lead to liver failure and may cause death.

After You Read Reviewing Facts and Vocabulary Digestion and absorption 1.What functions of the digestive system take place in the small intestine?

After You Read Reviewing Facts and Vocabulary 2.Describe the actions that cause food to move through the digestive tract. A series of involuntary muscle contractions, called peristalsis

After You Read Reviewing Facts and Vocabulary 3.What are three behaviors that help prevent indigestion? Sample answer: Eat less food, eat meals slowly, and chew food thoroughly.