The Digestion Process (Organs and Functions)

  • Medical Author:
    Jerry R. Balentine, DO, FACEP

    Dr. Balentine received his undergraduate degree from McDaniel College in Westminster, Maryland. He attended medical school at the Philadelphia College of Osteopathic Medicine graduating in1983. He completed his internship at St. Joseph's Hospital in Philadelphia and his Emergency Medicine residency at Lincoln Medical and Mental Health Center in the Bronx, where he served as chief resident.

  • Medical Editor: Bhupinder Anand, MD
woman with abdominal pain

The colon, rectum, and anus

The role of the lower GI tract is to solidify the waste product (by absorbing water), store the waste product until it can be evacuated (going to the bathroom) and help with the evacuation process.

The large intestine (colon) has four parts:

  1. ascending colon,
  2. transverse colon,
  3. descending colon and
  4. sigmoid colon.

All together the colon is approximately 7 feet long and connects to the rectum. Here as in most other parts of the GI system, the waste product is moved along by peristalsis. As the waste product passes through the colon, water is absorbed and stool is formed.

The stool from the colon is stored in the rectum. The anal sphincter provides the control over releasing stool or holding it. Once stool arrives in the rectum, a feedback to the brain makes the person aware of the need for a bowel movement. Voluntary control over the anal sphincter lets us hold the stool until we go to the toilet.

Three accessory digestive organs (pancreas, liver, gallbladder)

Three other organs are instrumental in the digestive process.

  1. Pancreas: Although the pancreas is mostly known for its blood sugar regulatory function with the production of insulin (as part of the endocrine system -- he insulin goesdirectly from the gland into the bloodstream), it is the main producer of digestive enzymes as part of the exocrine system (the enzymes produced by the gland pass through a duct into the intestines). These enzymes are released into the duodenum and help with the digestion of fats, proteins, and carbohydrates..
  2. Liver: The liver produces bile for fat digestion and elimination. In addition, nutrients are stored in the liver, and toxins and chemicals are filtered by liver.
  3. Gallbladder: Bile is stored and released from the gallbladder. When fatty food enters the duodenum, the gallbladder contracts and releases bile.

Medically reviewed by Martin E Zipser, MD; American Board of Surgery

REFERENCE: Stanford Health Library. Digestive System.

Medically Reviewed by a Doctor on 7/6/2015

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