The Digestive System

Digestive System is the breaking down of food in the body, into a form that can be absorbed and used or excreted. It is also the process by which the body breaks down food into smaller components that can be absorbed by the blood stream.

Types:Mechanical Digestion:

Mechanical digestion is the first step of the digestion process and begins immediately after ingestion.

Mechanical digestion is the actual process of mastication (chewing) of food by teeth, to break the ingested food into smaller pieces that are more readily digested through chemical digestion. This mastication is mixed with saliva, which contains some enzymes to begin the chemical digestion process. Mechanical digestion also involves the process known as peristalsis. Peristalsis is accomplished by smooth muscle within the body and is responsible for the movement of food through the intestinal tracts.

Mechanical digestion is the actual process of mastication (chewing) of food by teeth, to break the ingested food into smaller pieces that are more readily digested through chemical digestion.

This mastication is mixed with saliva, which contains some enzymes to begin the chemical digestion process. Mechanical digestion also involves the process known as peristalsis.

Peristalsis is accomplished by smooth muscle within the body and is responsible for the movement of food through the intestinal tracts.

Types:Chemical Digestion:

Chemical digestion is accomplished through the use of chemicals known as digestive enzymes. These enzymes and water are responsible for the breakdown of complex molecules.

These complex molecules, such as fats, proteins, and carbohydrates, are digested (broken down) into smaller molecules.

These smaller molecules can then be absorbed for use by cells. Digestive enzymes control reaction speed. The presence of these digestive enzymes accelerates the digestion process, where absence of these enzymes slows overall reaction speed.

Enzymes:Site of Enzyme Origin

Enzyme Nutrient It Breaks Down

Product Of Enzyme Action

Place of Enzyme Action

Salivary Glands

Salivary Amylase

Carbohydrates-sugars

Simple Sugars Mouth

Gastric glands Pepsin Proteins Amino Acid Stomach

Liver Bile Fats Emulsified Fats Small Intestine

Small Intestine

Maltase, Lactase, Sucrose

Carbohydrates Simple Sugars Small Intestine

Pancreas Lipase, Amylase

Proteins, Fats, Carbohydrates

Amino Acids, Glycerol, Simple Sugars

Small Intestine

Gastrointestinal Tract

MouthEsophagusStomachSmall IntestinePancreasLiverGall BladderLarge IntestineRectumAnus

Mouth

The mouth is the beginning of the digestive tract; and, in fact, digestion starts here when taking the first bite of food.Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use.

Esophagus

The esophagus seems to have only one important function in the body—to carry food, liquids, and saliva from the mouth to the stomach. The stomach then acts as a container to start digestion and pump food and liquids into the intestines in a controlled process. The esophagus transports food to the stomach by coordinated contractions of its muscular lining. This process is automatic and people are usually not aware of it.

StomachUsually “J” shapedThe stomach’s main function: storing the food we eat, breaking down the food into a liquidly mixture called chyme, mixing enzymes which is are chemicals that break down food, and slowly empties that liquidly mixture into the small intestine.The stomach is a hollow organ, or "container," that holds food while it is being mixed with enzymes that continue the process of breaking down food into a usable form. Cells in the lining of the stomach secrete a strong acid and powerful enzymes that are responsible for the breakdown process.

Small Intestine Large Intestine

The small intestines are responsible for absorbing most of the nutrients found within your food. By the time ingested food reaches the small intestine, it has been mechanically broken down into a liquid. As this liquid flows across the inner surface of the small intestine (which has many small folds to increase the surface area), nutrients within the food come into contact with the many small blood vessels which surround the small intestine.

The large intestine is the thick, lower end of the digestive system, containing the appendix, colon and rectum. Its principle function is to reabsorb water and maintains the fluid balance of the body. Certain vitamins are also taken in through the large intestinal wall. Further down the intestine, in the rectum, faces are stored waste before it is eliminated. Another function is to process indigestible material (fiber), which makes up the bulk of the waste

products.

Pancreas Liver

The pancreas secretes digestive enzymes into the duodenum, the first segment of the small intestine. These enzymes break down protein, fats, and carbohydrates. The pancreas also makes insulin, secreting it directly into the bloodstream. Insulin is the chief hormone for metabolizing sugar.

The main function of the liver is to process the nutrients absorbed from the small intestine. Bile from the liver secreted into the small intestine also plays an important role in digesting fat. The liver is the body’s chemical "factory." It takes the raw materials absorbed by the intestine and makes all the various chemicals the body needs to function. It breaks down and secretes many drugs.

Gall Bladder

The gallbladder stores and concentrates bile, and then releases it into the duodenum to help absorb and digest fats.The ingestion of food and especially fats cause the release of a hormone, cholecystokinin, (CCK) which in turn signals the relaxation of the valve at the end of the common bile duct (the sphincter of oddi) which lets the bile enter the small intestine. It also signals the contraction of the gallbladder which squirts the concentrated liquid bile into the small intestine where it helps with the emulsification or breakdown of fats in the meal.

Rectum and Anus

Rectum Anus The rectum (Latin for "straight") is an 8-inch chamber that connects the colon to the anus. It is the rectum's job to receive stool from the colon, to let the person know that there is stool to be evacuated, and to hold the stool until evacuation happens. When anything (gas or stool) comes into the rectum, sensors send a message to the brain. The brain then decides if the rectal contents can be released or not. If they can, the sphincters relax and the rectum contracts, disposing its contents. If the contents cannot be disposed, the sphincter contracts and the rectum accommodates so that the sensation temporarily goes away.

The anus is the last part of the digestive tract. It is a 2-inch long canal consisting of the pelvic floor muscles and the two anal sphincters (internal and external). The anus is surrounded by sphincter muscles that are important in allowing control of stool. The pelvic floor muscle creates an angle between the rectum and the anus that stops stool from coming out when it is not supposed to. The internal sphincter is always tight, except when stool enters the rectum. It keeps us continent when we are asleep or otherwise unaware of the presence of stool.