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Digestive System: Facts, Function & Diseases

The human digestive system is a series of organs that converts food into essential nutrients that are absorbed into the body and moves the unused waste material out of the body. It is essential to good health because if the digestive system shuts down, the body cannot be nourished or rid itself of waste.

Infographic: all about your stomach and how digestion works.

Description of the digestive system

The digestive tract, also known as the gastrointestinal (GI) tract, starts at the mouth, continues to the esophagus, stomach, small intestine, large intestine (commonly referred to as the colon) and rectum, and ends at the anus. The entire system — from mouth to anus — is about 30 feet (9 meters) long.

Digestion begins with chewing. Teeth, which are part of the skeletal system, play a key role in digestion. In carnivores, teeth are designed for killing and breaking down meat. Herbivores’ teeth are made for grinding plants and other food to ease them through the digestion process. Saliva, which is secreted by the salivary glands in the mouth, contains an enzyme, salivary amylase, which breaks down starch.

Swallowing pushes chewed food into the esophagus, where it passes through the oropharynx and hypopharynx. At this point, food takes the form of a bolus — a small round mass — and digestion becomes involuntary. A series of muscular contractions, called peristalsis, transports food through the rest of the system. The esophagus empties into the stomach.

The stomach’s gastric juice, which is primarily a mix of hydrochloric acid and pepsin, starts breaking down proteins and killing potentially harmful bacteria. After an hour or two of this process, a thick semi-liquid paste called chyme forms.

At this point the pyloric sphincter valve opens and chyme enters the duodenum, where it mixes with digestive enzymes from the pancreas and acidic bile from the gall bladder. The next stop for the chyme is the small intestine, a 20-foot (6-meter) tube-shaped organ where the majority of the absorption of nutrients occurs. The nutrients move into the bloodstream and are transported to the liver.

The liver creates glycogen from sugars and carbohydrates to give the body energy and converts dietary proteins into new proteins needed by the blood system. The liver also breaks down unwanted chemicals, such as alcohol, which is detoxified and passed from the body as waste.

Whatever material is left goes into the large intestine. The function of the large intestine, which is about 5 feet long (1.5 meters), is primarily for storage and fermentation of indigestible matter. Also called the colon, it has four parts: the ascending colon, the transverse colon, the descending colon and the sigmoid colon. This is where water from the chyme is absorbed back into the body and feces are formed primarily from water (75 percent), dietary fiber and other waste products. Feces are stored here until they are eliminated from the body through defecation.

Diseases of the digestive system

Many problems can affect the GI tract, including: abdominal pain, blood in the stool, bloating, constipation, diarrhea, heartburn, incontinence, nausea and vomiting and difficulty swallowing.

Among the most widely known diseases of the digestive system is colon cancer. This is typically a slow-growing cancer that is often survivable if caught early.

Many diseases and conditions of the digestive system — including irritable bowel syndrome, lactose intolerance, diverticulitis, GERD, Crohn’s disease, celiac disease, peptic ulcer and hiatal hernia — can be chronic and are difficult to diagnose and treat. Many of the diseases of the digestive system are tied to the foods we eat, and many sufferers must restrict their diets. [Tips for Preventing Stomach Aches]

There are a number of tests to detect digestive tract ailments. A colonoscopy is the examination of the inside of the colon using a long, flexible, fiber-optic viewing instrument called a colonoscope. Other testing procedures include upper GI endoscopy, capsule endoscopy, endoscopic retrograde cholangiopancreatography and endoscopic ultrasound.

Study of the digestive system

Gastroenterology is the branch of medicine focused on studying and treating the digestive system disorders. Physicians practicing this specialty are called gastroenterologists. The name is a combination of three ancient Greek words gaster (gastros) (stomach), enteron (intestine) and logos (reason). It is an internal medicine subspecialty certified by the American Board of Internal Medicine.

References to the digestive system can be traced back to the ancient Egyptians. Some milestones in the study of the gastrointestinal system include:

  • Claudius Galen (circa 130-200) lived at the end of the ancient Greek period and reviewed the teachings of Hippocrates and other Greek doctors. He theorized that the stomach acted independently from other systems in the body, almost with a separate brain. This was widely accepted until the 17th century.
  • In 1780, Italian physician Lazzaro Spallanzani conducted experiments to prove the impact of gastric juice on the digestion process.
  • Philipp Bozzini developed the Lichtleiter in 1805. This instrument, which was used to examine the urinary tract, rectum and pharynx, was the earliest endoscopy.
  • Adolf Kussmaul, a German physician, developed the gastroscope in 1868, using a sword swallower to help develop the diagnostic process.
  • Rudolph Schindler, known to some as the “father of gastroscopy,” described many of the diseases involving the human digestive system in his illustrated textbook issued during World War I. He and Georg Wolf developed a semi-flexible gastroscope in 1932.
  • In 1970, Hiromi Shinya, a Japanese-born general surgeon, delivered the first report of a colonoscopy to the New York Surgical Society and in May 1971 presented his experiences to the American Society for Gastrointestinal Endoscopy.
  • In 2005, Australians Barry Marshall and Robin Warren were awarded the Nobel Prize in Physiology or Medicine for their discovery of Helicobacter pylori and its role in peptic ulcer disease.

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