4/8/16. Digestive System. When you are hungry it is because your brain receives a signal from your cells that they need energy

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1 When you are hungry it is because your brain receives a signal from your cells that they need energy Section 1 Digestive System A group of organs that work together to digest food so that it can be used by the body The most obvious part of your digestive system is a series of tube-like organs called the digestive tract mouth pharynx esophagus stomach Other organs: Liver Pancreas small intestine large intestine rectum anus Gallbladder Salivary glands Digestion The process of breaking down food into a form that can pass from your digestive tract into the bloodstream Two types of digestion 1. Mechanical breaking, crushing, and mashing of food 2. Chemical large molecules are broken down into nutrients Nutrients substances in food that the body needs for normal growth, maintenance, and repair 1

2 1. Carbohydrates 2. Proteins 3. Fats Enzymes Substances that break some nutrients into smaller particles that the body can use For example, proteins are chains of smaller molecules called amino acids. Proteins are too large to be absorbed into the bloodstream. So, enzymes cut up the chain of amino acids. The amino acids are small enough to pass into the bloodstream. 1. Mouth 2. Esophagus 3. Stomach 4. Small Intestine 5. Large Intestine (colon) 6. Rectum 7. Anus Chewing is important for two reasons. 1. chewing creates small, slippery pieces of food that are easier to swallow than big, dry pieces are 2. small pieces of food are easier to digest important organs for mechanical digestion. break and grind food Enamel outermost layer of a tooth hardest material in the body protects nerves and softer material inside the tooth 2

3 As you chew, food mixes with saliva Saliva is made in salivary glands located in the mouth contains an enzyme that begins the chemical digestion of carbohydrates changes complex carbohydrates into simple sugars Once the food has been reduced to a soft mush, the tongue pushes it into the throat, which leads to a long, straight tube called the esophagus. Esophagus squeezes the mass of food with rhythmic muscle contractions called peristalsis Peristalsis forces the food into the stomach. Stomach muscular, saclike, digestive organ attached to the lower end of the esophagus. continues the mechanical digestion of your meal by squeezing the food with muscular contractions At the same time, tiny glands in the stomach produce enzymes and acid The enzymes and acid work together to break food into nutrients Stomach acid also kills most bacteria that you might swallow with your food Creates a soupy mixture called chyme 3

4 Most chemical digestion takes place after food leaves the stomach Proteins, carbohydrates, and fats in the chyme are digested by the small intestine and fluids from the pancreas Pancreas an oval organ located between the stomach and small intestine makes fluid that protects the small intestine from the acidity of the chyme fluid contains enzymes that chemically digest chyme and contains bicarbonate, which neutralizes the acid in chyme chyme never enters the pancreas, the pancreatic fluid flows into the small intestine pancreas also functions as a part of the endocrine system by making hormones that regulate blood sugar Small Intestine muscular tube that is about 2.5 cm in diameter small diameter but 6 m long Villi fingerlike projections that cover the inside wall of the small intestine surface area of the small intestine is very large because of the villi covered with tiny, nutrient-absorbing cells when nutrients are absorbed, they enter the bloodstream Liver large, reddish brown organ that helps with digestion can be as large as a football located toward your right side, slightly higher than your stomach produces bile 4

5 Gallbladder Small, saclike organ where bile is temporarily stored Bile A liquid that breaks large fat droplets into very small droplets squeezed from the gallbladder into the small intestine This mechanical process allows more fat molecules to be exposed to digestive enzymes After nutrients are broken down, they are absorbed into the bloodstream and carried through the body Nutrients that are not needed right away are stored in the liver The liver releases the stored nutrients into the bloodstream as needed The liver also captures and detoxifies many chemicals in the body For instance, the liver produces enzymes that break down alcohol and many other drugs. Material that can t be absorbed into the blood is pushed into the large intestine Large Intestine stores, compacts, and then eliminates indigestible material from the body has a larger diameter than the small intestine 1.5 m long and has a diameter of about 7.5 cm. Undigested material enters the large intestine as a soupy mixture large intestine absorbs most of the water in the mixture and changes the liquid into semisolid waste materials called feces, or stool. Whole grains, fruits, and vegetables contain a carbohydrate, called cellulose, that humans cannot digest. We commonly refer to this material as fiber Fiber keeps the stool soft and keeps material moving through the large intestine. 5

6 Rectum the last part of the large intestine stores feces until they can be expelled feces pass to the outside of the body through an opening called the anus It takes your food about 24 hours to make the journey through your body 6