Unit Four Digestive System Lisa Michelek 1

Digestion Digestion is the process that changes food into a form that can be used by the cells of your body. Food is taken in and processed through your digestive system before it can be used by your body. The usable parts of food (nutrients) supply you with the chemicals and energy you need to survive. The digestive process begins when food is taken into the body – ingestion. 2

Digestion Digestion begins with the breakdown of food into smaller pieces. This process is called mechanical digestion and it prepares the food for chemical digestion. During chemical digestion, large complex food molecules are chemically changed into smaller simpler molecules. In unicellular and other simple organisms, digestion is intracellular. This means that digestion takes place in vacuoles inside the cell of the organism. In larger, complex multicellular organisms, digestion is extracellular. 3

Mechanical Digestion In most organisms, food must undergo a mechanical breakdown called mechanical digestion, where food is physically cut, ground, and torn into smaller pieces. Mechanical digestion increases the surface area of the food particles, which prepares them for chemical digestion. 4

Chemical Digestion During chemical digestion, large organic molecules are broken down into small simple molecules by the chemical process of hydrolysis. During hydrolysis water is added to large complex molecules causing them to split into simpler molecules that can be used by the cells. Each reaction in digestion is catalyzed by a specific enzyme. These digestive enzymes help chemically break down foods and must be present for digestion to occur. 5

Chemical Digestion In all organisms, the complete chemical digestion of large molecules produces the end products shown in the below table. Large Molecules Enzymes End Products Carbohydrates Maltase Simple sugars Lipids Lipase Fatty acids and glycerol Proteins Protease Amino acids 6

Chemical Digestion Chemical digestion does not completely break down all food molecules. The organism may lack enzymes to digest some types of food molecules, or there may not be enough time for enzymes to digest the food completely. When this happens, the organism must eliminate indigestible or undigested materials. Egestion is the process by which heterotrophs (organisms that cannot make their own food) eliminate or remove food wastes from the body. 7

The Alimentary Canal The digestive system is made up of a continuous one-way tube that begins in the mouth and ends with the anus. This tube is commonly called the alimentary canal or gastrointestinal (GI) tract. As food passes through the tube, special areas of the tube mechanically and chemically change food. 8

The Alimentary Canal Food moves in one direction through the alimentary canal by slow, rhythmic, muscular contractions called peristalsis. After chemical digestion, the nutrients you eat pass from the alimentary canal into all the cells of the body. 9

The Alimentary Canal Ingestion takes place at the mouth, which is also called the oral cavity. This process begins mechanical digestion, which increases the surface area of the food. Chemical digestion also begins in the mouth. 10

The Alimentary Canal The salivary glands, located in the oral cavity, secrete saliva. Saliva has mucus that moistens food making it easier to swallow. 11

The Alimentary Canal Saliva also contains the enzyme ptyalin. Ptyalin starts the chemical digestion of starches. The starch in bread is changed into maltose, a disaccharide (double sugar). You can check this for yourself by chewing a piece of bread for a few minutes. When the starch in the bread is changed to sugar, you will notice a sweet taste. 12

The Alimentary Canal Besides aiding in mechanical digestion, the tongue is important during the tasting and swallowing of food. There are little groups of cells located in the tongue and roof of the mouth called taste buds. Four basic kinds of taste are sweet, sour, salty, and bitter. 13

The Alimentary Canal After food is swallowed, it goes into the esophagus. The esophagus or gullet is a tube that moves food from the mouth to the stomach by peristalsis. No additional chemical digestion begins in the esophagus. The chemical action of saliva continues in the esophagus until the food reaches the stomach. The esophagus produces a slimy material called mucus. Mucus lubricates (moistens) food so it slides down esophagus more easily. 14

The Stomach The stomach is a muscular, J-shaped organ. Mechanical digestion occurs when stomach muscles churn and mash food. The food becomes a thick soupy mixture called chyme. Chemical digestion also occurs in the stomach. 15

The Stomach Glands in the stomach lining secrete gastric juice and hydrochloric acid. Hydrochloric acid (HCl) destroys bacteria normally present in food and provides the proper pH for enzyme action. The gastric juice contains pepsin, an enzyme that begins the chemical digestion of protein. Rennin is an enzyme that begins the chemical digestion of milk protein. 16

The Small Intestine After three or four hours, partly digested food leaves the stomach and enters the small intestine. In the small intestine, food digestion is completed and digested nutrients are absorbed into the bloodstream. Most chemical digestion takes place in the small intestine, not in the stomach. 17

The Small Intestine In the small intestine, digestion is accomplished as a result of the action of enzymes produced by intestinal glands and the pancreas. Bile, made by the liver, prepares fats and oils for enzyme digestion by breaking them down into smaller pieces. 18

The Small Intestine This process greatly increases the surface area of fat particles, thereby speeding up fat digestion by enzymes called lipases. The action of bile on fats is referred to as a detergent effect, because detergent also breaks up fat. Bile is stored in the gall bladder and enters the small intestine through the bile duct. 19

The Small Intestine Lining the inside of the small intestine are tiny finger-like projections of the intestinal wall known as villi. Villi increase the surface area of the small intestine for the absorption of the end products of digestion. End products are absorbed by the process of diffusion. 20

The Small Intestine 21

The Large Intestine Undigested foods (wastes) pass from the small intestine into the large intestine. The large intestine is also called the colon. In the large intestine, water, some vitamins, and minerals are absorbed into the blood stream. The remaining undigested substances, called feces, are stored in the lower end of the large intestine called the rectum. Feces are eliminated from the body (egestion) through the anus. 22

End Products of Digestion The final compounds formed by digestion are called end products. These molecules are small and chemically simple so that they can be absorbed and used by the body’s cells. Once the end products of digestion enter a cell, the cell will use them as building blocks in the synthesis (making) of complex compounds (nutrients) necessary for life. This is done by the chemical process of dehydration synthesis. 23

End Products of Digestion Dehydration synthesis is the opposite of hydrolysis. Simple sugars are made into complex carbohydrates, fatty acids and glycerol are made into fats, and simple amino acids become complex proteins. Excess water was absorbed by the large intestine and what ever indigestible wastes were formed will be egested through the anus. 24

Digestive System Disorders Ulcers An ulcer is an open, painful sore in the stomach lining. Mucus, secreted by cells lining the surface of the stomach, helps to protect the stomach lining from hydrochloric acid. Open sores occur when there is too little mucus or too much acid in the stomach. Ulcers can bleed and sometimes eat completely through the stomach wall. Ulcers are treated with diet and medication. 25

Digestive System Disorders Tooth Decay Mouth bacteria cause tooth decay. Brushing and flossing your teeth at least once a day will help slow down the action of bacteria on food caught between your teeth. Regular visits to your dentist are also very important in preventing tooth decay and gum disease. 26

Digestive System Disorders Appendicitis Located near the beginning of the large intestine is a small finger like projection called the appendix. An infection of the appendix is called appendicitis. Treatment for this very painful condition is surgical removal of the appendix. If the appendix is not removed it may leak fluid into the surrounding membranes and organs, possibly leading to death. 27

Digestive System Disorders Diarrhea The condition in which the feces do not remain in the large intestine long enough for the water to be absorbed is called diarrhea. Diarrhea can be caused by bacteria or viruses, emotional stress, or eating certain foods. If diarrhea lasts for a long time the body becomes dehydrated (loss of water) resulting in weakness. Severe diarrhea can result in death. 28

Digestive System Disorders Constipation The opposite of diarrhea is constipation, a condition where the feces remain in the colon too long. Constipation can be caused by too little fiber or water in the diet. 29

Digestive System Summary https://www.youtube.com/watch?v=lm3oIX6jjn4