Digestion

=Why do we need to digest food? =

Fuctions of the Digestive System
__3 main functions__ - 1 - to break down food into small parts 2 - to absorb nutrients 3 - to eliminate wastes from body

There are 2 types of digestion: 1 - __Mechanical__ - occurs when you bite a sandwich and chew it into small pieces - happens in mouth and stomach 2 - __Chemical__ - chemicals (enzymes) produced by the body break down food into their smaller chemical block. Ex: starch in bread is broken down into individual sugar molecules.

After the food is digested, molecules are ready to be transported throughout the body. __Absorption__ - process by which nutrient molecules pass through the wall of the digestive system into blood. Fiber isn't absorbed, it's eliminated in body wastes.
 * Absorption and Elimination**

** The Mouth: **
Mechanical and chemical digestion start in the mouth. - It starts with the teeth **chewing** the food into smaller pieces. - The chemical digestion starts with the **saliva** breaking **starch** molecules into smaller sugar molecules. - What breaks up the starch molecules in the **enzyme AMYLASE** present in the saliva.
 * Mechanical digestion in the mouth:
 * Chemical digestion in the mouth:

(**Epiglottis** seals off your windpipe, preventing food from going to the lungs.)


Group 4: Bea, Luis, Mary  The Stomach:
The stomach is located in the abdomen and is J shaped. When you eat, and the food enters your stomach, it expands to be able to hold the food you swallow. There are 2 kinds of digestion that take place in your stomach, **mechanical** and **chemical** digestion. In mechanical digestion, strong muscles help mix the food. Chemical digestion is when digestive juice, produced by cells that line the stomach, mixes with the churning food. Digestive juice containsthe enzyme **pepsin** which chemically digests the proteins in your food, and breaks them down into short amino acid chains. It also contains a very strong acid, **hydrochloric acid**, which your stomach could not function without; it kills bacteria you swallow in food and pepsin works best in an acid environment. The reason the acid doesn’t burn your stomach is because the cells lining the stomach produce **mucus**, which protects it. Food stays in the stomach until it has been broken down into thick liquid, which then goes on into the next part of the digestive system, where the final chemical digestion and absorption will take place.

** The Small Intestine: **
The **small intestine** is where most chemical digestion takes place. - **Liver**: is located in the upper right portion of the abdomen. It produces bile.The liver is the biggest organ in the body. - **Bile**: is a substance that helps break up fat particles into smaller particles to facilitate the job of enzymes. - **Gallbladder**: the organ that stores bile. Almost all chemical digestion and absorption of nutrients takes place in the small intestine. As the liquid moves into the small intestine, it mixes with enzymes and secretions that are produced by the small intestine, the liver, and the pancreas. When food passes by the small intestine, it has already been chemically digested into a thick liquid.

The Pancreas:
The small intestine is full of finger-shaped structures called **villi**. Nutrients molecules pass from the inside of the small intestine into the blood vessels inside the villi. Villi greatly increase surface area and make absorption much faster.
 * Pancreas** is a triangular organ located between the stomach and the first part of the small intestine. The pancreas produces enzymes that flow into the small intestine. They help break down starches, proteins and fats. The pancreas also produces BICARBONATE which makes juice alkaline (basic). This is important to neutralize the acid food coming down from the stomach.

 The Large Intestine:
The large intestine is the final part of the digestive system. As the waste passes through the large intestine, the water is absorbed into the bloodstream. The bacteria feed on the waste, and also produce vitamin K. This vitamin is also absorbed in the large intestine. The large intestine ends in a small tube called the rectum, that pushes the waste out through the anus.