03-29-07, Digestive system

Before your body can use nutrients in the food you consume, the nutrients must be broken down both physically and chemically. The process of breaking down food into molecules the body can use is called digestion. The digestive system is actually a long hollow tube called the gastrointestinal tract (GI tract).

The digestive system includes: mouth, pharynx, esophagus, stomach, small intestine, large intestine, colon, and the anus. Several major organs are along the gastrointestinal tract aid in digestion. The salivary glands, the pancreas and the liver add secretions to the digestive system tract so that the compounds can be broken down and eventually absorbed.

Those organs are not a part of the gastrointestinal tract. There are three activities that are involved in the digestive process. There is mechanical digestion, chemical digestion and absorption.

Step 1: break down food into fine pulp without changing chemical structure of the food. This occurs in the mouth and consists of mechanical chewing and the introduction of salivary to the food. Increase surface area.

Step 2: Chemicals act on food breaking it down to smaller particles so that it can be absorbed into the blood.

Step 3: Absorb nutrients and pass them to blood to be transported over the body. This is a lot like the respiratory system, but the respiratory system was easier because the problem of extracting oxygen from the air is simple enough, but the problem with the digestive system is that nutrients and molecules are already in some structures and so on, it's not readily available for absorption and definitely not in a state that our bodies are likely familiar with or able to cope with (you don't send pizza down your arteries and veins directly).

Mechanical and chemical digestion begins in the mouth, otherwise known as mastication. During chewing, salivary glands produce saliva, a mixture of water, mucus and salivary amylase.

Enzymes in the saliva (like amylase) kill bacteria and begin the process of chemical digestion by breaking down starches to sugars. Starches are long chains of sugar molecules because starches are polypeptides. Saliva is produced by three sets of glands located near the mouth.

The mucus in the saliva softens and lubricates food and helps hold the food together, a comparison can be made with the pleura membrane here which makes sure that the lungs do not hit the rib cage (which is extremely painful).

Salivary amylase begins the chemical digestion of carbohydrates by breaking down some starch into disaccharide maltose.

The structure of the stomach is such that there are gastric pits. These are little tiny holes that the juices dip into and become further digested.