What is it?

The digestive tract, one of the largest of all body systems, extends approximately 30 feet long and extends as a long continuous tube, from mouth to anus! This system is unique in that it is strictly speaking "outside the body".  That is, it's long continuous tube communicates with the outside world. The diagram to the right shows this.

The digestive system is divided into regions that specialize in the process of digestion. The tract is primarily composed of a layer of cells, that secrete digestive juices and mucous as well as absorb nutrients, surrounded by muscle. It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. We'll describe the digestive process in detail.

When we eat such things as bread, meat, and vegetables, they are not in a form that the body can use as nourishment. Our food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body.

Digestion is the process by which food and drink are broken down into their smallest parts so that the body can use them to build and nourish cells and to provide energy.  Moving constantly and slowly, the digestive tract and it's accessory organs of digestion (the liver, gallbladder and pancreas) are faced with the task of converting all the foods we eat (from apples to zuchinni) into energy that supports and supplies the brain, the heart and the entire body. Impressively, the digestive tract can digest and absorb about 95 percent of nutrients, water, and electrolytes eaten (that is if we eat foods that don't harm it's environment).

In many senses, the digestive system resembles our car's gas tank. The food we eat is the fuel or gas that the digestive system (or fuel tank), converts into combustible power and energy needed to make our muscles move, carry out bodily functions, and repair and rebuild tissue. The digestive tract also functions as an immune organ, serving as a protective barrier to ingested toxins, allergens, and pathogens (bacteria, parasites, viruses, and fungi) that could otherwise cause disease.

The process of digestion begins with chewing. Chewing breaks up food into smaller pieces that can be swallowed without choking. The salivary glands secrete a mucous solution into the mouth that moistens and lubricates food particles. Saliva contains an enzyme that begins to digest carbohydrates. As food particles begin to dissolve, they react with the chemoreceptors in the mouth, giving rise to the sensation of taste.

The Diaphragm

The diaphragm is a dome-shaped sheet of skeletal muscle that separates the abdominal and thoracic (the area of the chest containing the heart and lungs) cavities. It is the principal muscle of respiration. Find more information on the diaphragm here.

The large, hollow organs of the digestive system contain muscle that enables their walls to move. The movement of organ walls can propel food and liquid and also can mix the contents within each organ. Typical movement of the esophagus, stomach, and intestine is called peristalsis. The action of peristalsis looks like an ocean wave moving through the muscle. The muscle of the organ produces a narrowing and then propels the narrowed portion slowly down the length of the organ. These waves of narrowing push the food and fluid in front of them through each hollow organ.

The first major muscle movement occurs when food or liquid is swallowed. Although we are able to start swallowing by choice, once the swallow begins, it becomes involuntary and proceeds under the control of the nervous system

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