Digestive System Digestive System Learning Goals Understand the

Digestive System

Digestive System Learning Goals �Understand the structure and function of the digestive system. �Identify techniques that keep the digestive system healthy.

Lets get a quick visual of the system and how it works! �Animation of the Digestive System

3 Main Functions �a. Digestion –the breaking down of food into smaller nutrient molecules the body can use. ◦ There are two types of digestion: �Mechanical digestion- foods are physically broken down into smaller pieces (chewing) �Teeth work in mechanical digestion �Chemical digestion- chemicals produced by the body break foods into their smaller chemical building blocks. �Saliva contains enzymes that break down food

�b. Absorption – the process by which nutrient molecules pass through the wall of your digestive system into your blood. �c. Elimination – Materials that are not absorbed, such as fiber, are eliminated from the body as wastes.

A Tour of the Digestive System

The Digestive Process Mouth �a. The entrance- inside the mouth ◦ When your body gets ready to eat, it will increase the production of saliva, or spit. �Saliva plays an important role in both types of digestion �It moistens the food to help chew it and to make it slippery so that it goes down easier. �It contains enzymes, which are a protein that speeds up chemical reactions to begin breaking down food chemically.

◦ Your teeth carry out the first step of mechanical digestion. �Mastication- chewing � Your cent teeth, incisors, cut the food into smaller pieces. � Your sharp point teeth, canines, tear the food into smaller pieces. � Your back teeth, molars, crush and grind the food.

The Journey Downward �a. When food leaves the mouth it travels down the esophagus, a muscular tube that connects the mouth to the stomach. ◦ It is lined with mucus, a thick slippery substance that makes it easy to swallow. ◦ Food passes the trachea (windpipe) which is blocked by a little flap called the epiglottis. ◦ Food is moved down the esophagus by waves of muscle contractions called peristalsis. �Strong enough to push food up if you swallowed food while standing on your head (similar to squeezing a tube of toothpaste from the bottom up)

Peristalsis � 3 D Animation of Peristalsis in the Large Intestine �Endoscopy of Gastric Antrum

First Stop- The Stomach �a. The stomach is a J shaped pouch. �b. It can expand 50 times its normal size to hold the food we eat. �c. Most mechanical and chemical digestion take place here. ◦ Mechanical- 3 strong layers of smooth muscle contract to produce a churning motion. This mixes food and fluids much like a washing machine does clothes and soapy water.

◦ Chemical- The lining of the stomach produces gastric juices, which have two primary ingredients. �Pepsin- an enzyme that breaks proteins down into smaller building blocks called amino acids. Pepsin works best in an acidic environment. �Hydrochloric Acid- helps break food down as well as killing many bacteria that you swallow with your food. The stomach is lined with mucus to protect it form the acid- the cells in the stomach produce a thick mucus and are replaced very quickly

�Food remains in the stomach until all of the solid material has been broken down into a thick liquid form called chyme. This is then released into the lower part of the digestive system, starting with the small intestine.

Second Stop- The Small Intestine �Why is it called the small intestine? ◦ The small intestine is about 6 meters long making up about 2/3 of the length of the whole digestive system. ◦ So why is it called the small intestine? Because with a diameter of only 2 -3 centimeters wide, it is about half the diameter of the large intestine.

�Almost all chemical digestion and absorption of nutrients takes place in the small intestine. ◦ Starches and proteins have been partially broken down by now, but fats have not been digested at all. ◦ Enzymes and secretions from the liver and pancreas mix with those of the small intestine to break down the food even further.

�The liver is the largest organ in the body and is like an extremely busy factory aiding in chemical digestion and plays a role in many body processes. (Ex. Breaking down medicines) �For digestion the liver produces bile, a substance that breaks down fat particles. Bile is stored in the gallbladder- travels to the small intestine after you eat. � Bile doesn’t chemically digest fat, it physically breaks the fat into smaller particles much like dishwashing liquid does in the sink. �The pancreas produces enzymes that then break down the fat chemically- also breaks down proteins and starches.

◦ After the food is broken down further, the small intestine absorbs nutrient molecules. �The inner surface of the small intestine is covered with villi, millions of tiny finger shaped structures filled with tiny blood vessels. These greatly increase the surface are of the intestine, making it about the size of a tennis court. �The nutrients pass through the cells of the villi into the bloodstream to be delivered to the rest of the body. �AT THIS POINT MOST NUTRIENTS HAVE NOW BEEN ABSORBED!

Third Stop- Large Intestine �This is the last section of the digestive system. �About 1. 5 meters long- about as long as a bathtub �Contains bacteria that feed on the material passing through. These bacteria are also helpful because they produce Vitamin K

�As the remaining material moves through the large intestine, water is absorbed into the blood stream. �The large intestine ends in a short tube called the rectum where the remaining waste material, feces is compressed into a solid form. �It is then eliminated from the body through the anus, a muscular opening at the end of the rectum.

Digestive System Care � 1. Eat foods high in fiber! ◦ Fiber helps food and waste pass through the digestive tract ◦ Reduces risk of colon cancer ◦ Beans, Prunes, Pears, and Leafy Green Vegetables are good sources

Digestive System Care � 2. Drink plenty of water ◦ 8 glasses a day! ◦ Helps keep things moving regularly

Digestive System Care � 3. Eat slowly and don’t hurry through your meals ◦ Eating too fast can cause gas or indigestion