Digestive & Urinary Systems Chapter 18 Digestive & Urinary Systems

Lesson 1: The Digestive System

What is the purpose of the digestive system?

What is the purpose of the digestive system? Allows the nutrients of food to be used by the body. Digestion takes place mainly in the stomach and small intestine, but other organs aid in the digestive process. This lesson will focus on each process/organ involved.

Health Terms Digestion Absorption Elimination Ingestion Mastication Peristalsis Gastric Juices Chyme Bile

Health Concepts Food is the body’s fuel. Digestion is both a mechanical and chemical process. Digestion begins with ingestion, the taking in of food, and ends with the elimination of wastes. Each organ of the gastrointestinal tract has a specific function.

Functions of the Digestive System Digestion: the mechanical and chemical breakdown of foods for use by the body’s cells.* Absorption: the passage of digested food from the digestive tract into the circulatory system. * Elimination: the expulsion of undigested food or body wastes. Once food is broken down, nutrients from it are absorbed through the small intestine. The nutrients then pass along to the circulatory system. Any food that is not broken down in this process is eliminated in the form of wastes.

Structure of the Digestive System Mouth & Teeth Esophagus Stomach Small Intestine Large Intestine

Mouth & Teeth Many structures are involved in ingestion, the taking of food into the body, which is the earliest stage of digestion.* The Teeth: Primary function is to break the feed you eat into smaller pieces so it can be swallowed. Mastication – the process of chewing. Types of teeth Incisors – shear food Canines – rip Molars – grind By chewing, food is broken down into smaller particles, increasing the surface area of the food that is exposed to digestive juices. Efficient for getting greatest amount of energy from what we eat.

Mouth & Teeth continued… The Salivary Glands: Three pairs in the mouth secrete saliva (watery solution containing an enzyme that starts the digestion of carbohydrates). Saliva also lubricates your food, making it easier to swallow.* The Tongue: Forms food into a ball for easier swallowing. As you swallow food is forced into pharynx. Uvula closes over the opening to nasal passages. Epiglottis closes to keep food from entering respiratory system. If the epiglottis opens food may enter windpipe (reflex causes us to cough to force food from windpipe). Example = laughing while swallowing*

The Esophagus Muscular tube that extends from pharynx to the stomach.* About 10 inches long. A process called peristalsis – a series of involuntary muscular contractions * – moves food through the esophagus. Solid food takes about 9 seconds to get through. A sphincter muscle allows food to move from esophagus to stomach. When relaxed, forms an opening. When contracted, opening closes. Sphincter muscles located in digestive tract protect food from backing up.

The Stomach Hallow, saclike organ enclosed in a muscular wall (3 layers). Flexible, allowing expansion when eating. Main activities: Continue the breakdown of food Storage until food is ready to enter small intestine Mix food and gastric juices (secretions from stomach lining that contain pepsin and hydrochloric acid). Control rate at which food enter small intestine. As stomach fills, layer of muscle produce contractions that churn food & gastric juices together. Produces chime (creamy fluid of food and gastric juices). Peristalsis moves the chime into the small intestine.

The Small Intestine The major part of digestion. Absorption occurs here. 20-23 feet in length and 1 inch in diameter. Consists of 3 parts: duodenum (chyme enters), jejunum, ileum (opens into large intestines). Peristalsis moves chime through small intestine for 3-5 hours. Small intestine is lined with villi (network of capillaries). These villi absorb digested food particles. Once absorbed they are carried throughout the body by the blood.* Unabsorbed materials leave small intestine in the form of liquid and fiber, moving by peristalsis into large intestine.

The Large Intestine (aka colon) 5-6 feet long and about 2 ½ inches in diameter. Movement of undigested food materials in large intestine is very slow. Main functions are to absorb water and eliminate undigested food.* Water, vitamins, and minerals are absorbed into the bloodstream. Many harmless bacteria normally live in the large intestines, changing the consistency of undigested food to a semisolid waste called feces. Feces pass from the body through the anus and is excreted as a bowel movement.

Organs That Aid Digestion Liver 2nd largest organ in your body (skin is # 1). Body’s chemical factory and regulates most of the main chemicals in your blood. The liver acts to clear the blood of drugs and poisonous substances. The liver absorbs the substances, changes their chemical structure, and makes them water-soluble. It then excretes (gets rid of) them in bile, a yellowish-green, bitter fluid important in the breakdown of fats.* Bile flows through the hepatic duct to the gallbladder, where it is stored.

Organs That Aid Digestion The Gallbladder A small, pear-shaped sac 3 to 4 inches long and located underneath the liver. Duct connects the gallbladder to the first section of the small intestine (duodenum). When food moves into the duodenum, bile (which is stored in the gallbladder) is released to break down fats contained in the food.

Organs That Aid Digestion The Pancreas Part of the endocrine system. Producer of insulin. Also produces 3 digestive enzymes:* Trypsin – digests proteins Amylase – digests carbohydrates Lipase – digests fats

Did You Know? The hydrochloric acid your stomach produces is strong enough to dissolve metal. In fact, if it were not for the mucus your stomach produces to form a protective lining, your stomach would digest itself!* Despite the stomach’s protective mucus, 500,000 cells of the lining are destroyed by the acid in the gastric juices every minute and must be replaced. Walking after eating helps digest food 40 to 50 percent faster. A person can digest food even if his or her stomach has been removed. The entire lining of the stomach is replaced every three days.

Define Terms & Questions (page 416: 1-5) Trace the path a bite of pizza follows until it is absorbed into the bloodstream. Describe the three different functions of the digestive system. Define the following terms and use each in a sentence: mastication, peristalsis, saliva, bile. Support the following statement: The real work of the digestive system is done in the small intestine. Explain in what way chewing food well contributes to the health of the digestive system.