The Digestive System

II- Trace the Digestion of fat starting from your mouth The digestive system is made up of the digestive tract and other organs that aid in digestion. The digestive tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus, consisting of the following: • • • • • • •

mouth esophagus stomach small intestine large intestine rectum anus

Organs that help with digestion, but are not part of the digestive tract, include the following: • • • • •

tongue glands in the mouth that make saliva

pancreas liver gallbladder

Parts of other organ systems, like nerves and blood, also play a major role in the digestive process. III- How is a piece of meat digested in your digestive system? Food is traveling in a wave-like movement called peristalsis, muscles propel food and liquid along the digestive tract. In general, there are six steps in the process of moving food and liquid through the digestive system: 1. The first major muscle movement is swallowing food or liquid. The start of swallowing is voluntary, but once it begins, the process becomes involuntary and continues under the control of the nerves.

2. The esophagus, which connects the throat above with the stomach below, is the first organ into which the swallowed food goes. 3. Where the esophagus and stomach join, there is a ringlike valve that closes the passage between the two organs. When food nears the closed ring, the surrounding muscles relax and allow the food to pass into the stomach, and then it closes again. 4. The food then enters the stomach, which completes three mechanical tasks: stores, mixes, and empties. First, the stomach stores the swallowed food and liquid, which requires the muscle of the upper part of the stomach to relax and accept large volumes of swallowed material. Second, the lower part of the stomach mixes up the food, liquid, and digestive juices produced by the stomach by muscle action. Third, the stomach empties the contents into the small intestine. 5. The food is digested in the small intestine and dissolved by the juices from the pancreas, liver, and intestine, and the contents of the intestine are mixed and pushed forward to allow further digestion. 6. Last, the digested nutrients are absorbed through the intestinal walls. The waste products, including undigested parts of the food, known as fiber, and older cells that have been shed from the mucosa, move into the colon. Waste products usually in the colon remain for a day or two until the feces are expelled by a bowel movement. IV- Discuss the role of Vitamins DNA is like template for different enzymes. Enzymes help cells to carry out chemical reactions. A cell is really just an extremely sophisticated chemical machine. A vitamin is a small molecule that your body needs to carry out a certain reaction. Your body has no way to create vitamin molecules Some Formulas itself, so the vitamin molecules must come in Vitamin A: C20H30O through food that you eat. Vitamins are classified Vitamin B1: C12H16 N4OS as either water-soluble, meaning that they dissolve Vitamin C: C6 H8 O6 easily in water, or fat-soluble, and are absorbed through the intestinal tract with the help of lipids. Each vitamin is typically used in multiple reactions and, therefore, most have multiple functions.

In humans there are thirteen vitamins, divided into two groups; four fat-soluble vitamins (A, D, E and K), and nine water-soluble vitamins (eight B vitamins and vitamin C).The human body is known to need at least 13 different vitamins: Vitamin A (fat soluble) - Retinol; comes from beta-carotene in plants (When you eat beta-carotene, an enzyme in the stomach turns it into Vitamin A.) • Vitamin B (water soluble):  B1 - Thiamine  B2 - Riboflavin  B3 - Niacin  B6 - Pyridoxine  B12 - Cyanocobalamin  Folic acid • Vitamin C (water soluble) - Ascorbic acid • Vitamin D (fat soluble) - Calciferol • Vitamin E (fat soluble) - Tocopherol • Vitamin K (fat soluble) - Menaquinone • Pantothenic acid (water soluble) • Biotin (water soluble) Inside the body, vitamins are used in many unique ways. For example, one of vitamin A's main roles is in the production of retinal. Retinal is used within the rods and cones in your eyes to sense light. There is no way for your body to produce retinal without vitamin A, and without retinal you cannot see. •

The different B vitamins are often embedded within the structure of different enzymes that a cell produces. For example, aspartate aminotransferase is an enzyme that transfers amines between amino acids. Each copy of the enzyme contains two vitamin B6 molecules, and without these molecules the enzyme cannot do anything. One use of Vitamin C is in the formation of collagen. Collagen is produced by special ribosomes in certain cells, and then exported from the cells to form collagen networks. During the process of collagen formation, the body must manufacture hydroxylproline from the amino acid proline. Vitamin C is essential to this reaction. Without vitamin C, collagen cannot be produced -- the first signs of this are very weak (and easily broken) blood vessels and loose teeth (which are held in their sockets by collagen). The body is able to store some vitamins, such as vitamin A (up to a year's supply is stored in your liver). Other vitamins need to be re-supplied frequently.