The Digestive System

The intestines are folded, coiled tubes that receive chyme from the stomach and then finish digestion. The intestines have two regions. Small intestine Large intestine

Chyme enters the small intestine first, and then it proceeds to the large intestine. Like the esophagus, the intestines use peristalsis to move chyme forward.

The body expels feces through the anus when enough waste builds up in the rectum.

Defecation is necessary to normal, healthy functioning of the digestive system. If you delay defecation, feces temporarily returns to the colon, where more water is absorbed. Feces that reenters the colon too many times may harden and obstruct the gastrointestinal tract.

Most absorption of nutrients occurs in the small intestine. The length of the small intestine gives it a large surface area. As chyme passes along this surface, cell walls absorb nutrients and pass them into the bloodstream. The bloodstream then distributes the nutrients throughout the body.

Absorption is only possible when bile and digestive enzymes have accomplished full digestion of the chyme in the small intestine.

The small intestine needs bile and digestive enzymes to break down food completely so that nutrients can be absorbed. These substances are supplied by other organs. The liver produces and then sends bile to the small intestine through the gallbladder. The pancreas produces digestive enzymes that break fats, carbohydrates, and proteins into small particles that can be absorbed.

Both organs release their digestive enzymes into the small intestine when food enters the lower gastrointestinal tract.

The digestive system serves three functions.

Breaking down food into nutrients and waste Absorbing nutrients Removing waste from the body

Digestion is the extraction of valuable nutrients from food. The organs in the gastrointestinal tract digest the following substances. Fats - compounds dense in calories (a measure of food energy) Proteins - complex chains of amino acids (basic elements of muscle) Carbohydrates - chains of sugar molecules Vitamins - compounds necessary in small amounts Minerals - elements such as calcium, sodium, and potassium

Digestion separates food into these basic elements and breaks them down into their simplest forms. Chewing and peristalsis grind food into a paste, and then acids and enzymes reduce the individual carbohydrates, fats, and other elements into simple forms that the intestines can absorb. The digestive process also absorbs water. When water and nutrients have been absorbed, the remainder is feces.

The stomach is a muscular sac that receives food from the esophagus. It can shrink or expand in size. The stomach holds onto food and continues digestion by releasing gastric juice. Gastric juice is a mixture of hydrochloric acid and other substances that break down food.

Food that the stomach has processed with gastric juice is called chyme. The stomach slowly releases chyme into the intestines, which you will learn about later.

Digestion begins in the mouth. Food that enters the mouth is partly broken down by the process of chewing. The following structures are found in the mouth. Teeth - the hard, bony structures that chop and grind food Tongue - the fleshy, muscular organ that moves food around the mouth Salivary glands - the glands that release saliva, a mixture of water and enzymes that dissolves the structures that bind food together

Glands are organs that create and release substances such as enzymes. Enzymes are substances that increase the rate at which any process, like digestion, occurs.

The appendix is a small organ attached to the beginning of the large intestine. The appendix is a vestigial organ, which is an organ that no longer serves any purpose in the body.

Its function in mammals is to host the bacteria that enable them to digest cellulose, a type of plant fiber. Human beings no longer need to digest cellulose, but a small version of the appendix remains.

Mastication is the process of chewing food, and it is the first step of the digestive process. During mastication, your teeth grind food into a paste that can be swallowed into the esophagus and stomach.

Mastication is aided by saliva, which contains the first of several digestive enzymes that food encounters along the gastrointestinal tract. The salivary glands located around your mouth release saliva as you begin chewing food.

The digestive system is a complex series of organs that processes food. An organ is a set of tissues that work together to accomplish a task. A tissue is a group of similar cells that work together. A cell is the basic structural and functional unit of life.

Most of the digestive organs form a tube that breaks food down into nutrients and waste. The other organs create and release digestive chemicals that aid in breaking down food.

The organs of the digestive system together form a tube that runs through your body. This tube is called the gastrointestinal tract, or the GI tract.

The GI tract is divided into two regions: the upper gastrointestinal tract and the lower gastrointestinal tract.

The large intestine absorbs water and salt from the indigestible material passed on by the small intestine. The large intestine is also home to a large colony of friendly bacteria, which are single-celled organisms.

The bacteria that live in the large intestine survive by digesting some of the indigestible material. The large intestine absorbs vitamins produced by the bacteria, such as vitamin K, which is important for normal blood clotting. As water is extracted from the chyme, it condenses into feces, which is composed mostly of indigestible food and bacteria.

The esophagus is a tube-shaped series of muscles that connects your mouth and pharynx to your stomach. It runs from the top of your chest down to your abdomen. A piece of food that is chewed and swallowed and then passes through the esophagus is called a bolus (from the Latin word for ball).

The esophagus repeatedly contracts and relaxes its muscles to create a "wave" that squeezes the bolus of food down to the stomach. This wave of contractions is called peristalsis.

Other organs assist digestion by storing or secreting (producing and releasing) substances that break down food into nutrients.

The following organs perform this function. Liver Pancreas Gallbladder They all assist digestion in the lower gastrointestinal tract. You will learn more about these organs later in the lesson.

The large intestine is a tube that receives food from the small intestine. The average length of the large intestine in adults is about one and one-half meters (five feet). The large intestine is "large" because it is wider (larger in diameter) than the small intestine.

The large intestine absorbs salts, vitamins, and the majority of the water that remains in digested food. The large intestine moves any indigestible food to the rectum, where it exits the body.

Not all organs of the digestive system are part of the gastrointestinal tract. Food never passes through the liver, gallbladder, or pancreas, but all three contribute digestive substances to the small intestine.

The liver is a large, multifunctional organ that connects to the small intestine through the gallbladder, the muscular sac where bile is stored until needed for digestion. Bile is a substance that dissolves fat into digestible particles. The pancreas is an organ that generates hormones and enzymes. Hormones are chemicals that instruct cells to perform a specific action.

The lower gastrointestinal tract consists primarily of the intestines. They absorb nutrients from food and expel waste from the body.

The liver, gallbladder, and pancreas contribute to the process of digestion, even though chyme never passes through them

The region of the digestive system that runs from the end of your stomach to the rectum is the lower gastrointestinal tract.

The lower gastrointestinal tract is composed of the following organs. Small intestine Large intestine, which also includes: appendix rectum

The pharynx is the area of the throat that connects the mouth to the esophagus, a muscular tube that connects the mouth to the stomach. When you swallow food, the tongue contracts to push food down through the pharynx toward the esophagus.

The pharynx also connects the air channels of the nose to your windpipe, a tube that brings air to the lungs. To prevent swallowed food from entering your windpipe, a flap called the epiglottis blocks off the windpipe when you swallow.

The final section of the large intestine is called the rectum. Food that reaches the rectum has been drained of nutrients and water. The remaining waste is called feces.

The rectum stores feces until the body is ready to expel it. Feces exits through the anus, an opening between the buttocks. As the rectum fills with feces, its walls stretch and send a signal to the brain that defecation must occur. Defecation is the process of using peristalsis to push feces out through the anus.

The small intestine is a long tube that coils to fit in the human body. The average length of the small intestine is just under six meters (twenty feet).

The small intestine is "small" because it is narrower (smaller in diameter) than the large intestine. Food is thoroughly digested as it moves through the small intestine. The walls of the small intestine absorb water, fats, proteins, and carbohydrates.

The presence of food expands the stomach and triggers the release of gastric juice. The acid and enzymes in gastric juice unravel proteins and dissolve all food into chyme, which has the form of paste.

The stomach releases chyme into the small intestine slowly so the lower gastrointestinal tract has time to process and absorb the nutrients. The stomach can absorb some water and alcohol on its own. When the stomach has emptied all of its chyme into the small intestine, it shrinks.

The region that runs from your mouth to your stomach is the upper gastrointestinal tract.

The upper gastrointestinal tract is composed of four organs. Mouth Pharynx Esophagus Stomach

The upper GI tract begins the process of digestion and stores chewed and swallowed food.

When you chew and swallow food, muscle contractions in the upper GI tract push food down to the stomach, where acids further dissolve its structure. The stomach also stores food until the lower GI tract is ready for it.

The digestive system is the gateway to the body for water and nutrients. The digestive system absorbs water and nutrients through the walls of its organs. These nutrients provide your body with energy. This process of extracting valuable nutrients from food is called digestion.

Without digestion, your body would not have the ability to grow or repair itself.