The Digestive System Food must be broken down into nutrients in a process called digestion. The breaking down of food into simpler substances for use by the body is the work of the digestive system. Functions of the Digestive System First to break down food into molecules the body can use Then the molecules are absorbed into the blood and carried throughout the body Finally, wastes are eliminated from the body The Mouth Chemical Digestion involves: 1. Salivary glands produce and release saliva. a. Function of saliva is to help moisten food 2. Ptyalin is an enzyme in saliva that breaks down some starches into sugars 3. Enzymes are proteins that speed up a chemical reaction. Enzymes are specific to what they will catalyze (increase the rate of). **The digestion of foods by enzymes is called chemical digestion.** Mechanical Digestion: 1. All of the following body parts in the mouth are involved in mechanical digestion: teeth, lips, and tongue. 2. Mechanical digestion is the physical action of breaking down food into smaller parts. Taste Buds 1. There are four types of taste buds: sweet, sour, salty, and bitter.
The Epiglottis 1. Epiglottis- flap of tissue that prevents food and water from going into your lungs The epiglottis automatically closes over the windpipe as you swallow your food. When you swallow, smooth muscles near the back of your throat begin to force the food down. It prevents food or water from moving into the windpipe or “going down the wrong pipe”. 2. Windpipe- tube through which the air you breathe reaches your lungs. The Esophagus 1. Esophagus- pipe-shaped tube that transports food into the stomach Esophagus comes from a Greek word meaning “to carry what is eaten”. After you swallow, smooth muscles force the food into the esophagus. The esophagus transports the food into the stomach by the process of peristalsis. Peristalsis- powerful wave of muscle contractions that pushes food through the digestive system. Digestion in the Stomach 1. As food enters the stomach a gastric juice is released. The gastric juice contains the enzyme pepsin, hydrochloric acid (HCl), and mucus. Pepsin is an enzyme produced in the stomach to digest protein. Mucus coats and protects the stomach wall. HCL is used to dissolve food and kill microorganisms. 2. The stomach uses both chemical and mechanical digestion.
Chemical digestion occurs when HCl and pepsin break down complex proteins into simpler proteins. Mechanical digestion occurs when muscle contractions mix the food with the gastric juice as peristalsis pushes the food toward the stomach’s exit. The food in your stomach is now a soft, watery substance. Digestion in the Small Intestine 1. The food in your stomach now moves slowly into the small intestine. The small intestine is an organ in which most digestion takes place and nutrients are absorbed. Food moves through the small intestine by peristalsis. Diameter of the small intestine is @ 2.5 cm. Length of small intestine is @ 6 meters. 2. Cells that line the walls of the small intestine release intestinal juice containing enzymes which aid in the digestive process. The intestinal juice of the small intestine has helper juices that are produced by two organs near the small intestine: the liver and the pancreas The liver and pancreas are considered to be digestive helpers because no food passes through them. The Liver The liver is an organ that produces bile and breaks down excess amino acids. It is also the largest and heaviest internal organ in our body. A. Location is to the right of the stomach. B. An important function of the liver is to aid in digestion by producing a substance called bile. C. Once the liver produces bile, the bile moves into the gallbladder. Gallbladder is an organ that stores bile. i. The gallbladder releases bile through a duct into the small intestine.
ii. Function of bile is to break up large fat molecules into smaller ones. The Pancreas The pancreas is an organ that produces pancreatic juice and insulin. Pancreatic juice is a mixture of enzymes. These enzymes move into the small intestine and help break down proteins, starches, and fats. The pancreas also produces insulin which is a hormone. These hormones are released directly into the bloodstream. Location of pancreas is between the stomach and small intestine. The Large Intestine The Large intestine is an organ in which its main function is to absorb water. It is also called the colon. It receives approximately 10 liters of water per day. 1.5 liters is from food and 8.5 liters is from secretions into the gut. 95% of this water is reabsorbed. If water is not absorbed, diarrhea can result, causing dehydration. Feces is composed of approximately 75% water and 25% solids. One-third of the solids is intestinal bacteria, 2/3’s is undigested materials. The last 20 cm of the large intestine is the rectum. Undigested food travels to the large intestine where water is removed. Helpful bacteria feed off of undigested food to create vitamins you need.