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10 Facts About Your Digestive System

How Digestion Works

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Updated February 14, 2013

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

10 Facts About Your Digestive System
Photo@A.D.A.M.

Like most things related to our bodies, we only pay attention to our digestive system when it's giving us a problem. Otherwise, we tend to overlook it and put all sorts of things into it without a second thought. Although we learn about the process of digestion in high school, most of us had other things on our minds back then. But knowing how your digestive system is supposed to work can help tremendously in terms of overall digestive health - knowledge which can help you take better care of your digestive system, more quickly identify any possible digestive problems, and help you to communicate more effectively with your doctor.

1. The length of your entire digestive system from mouth to anus is approximately 30 feet long.

Your digestive system is responsible for breaking down the foods you eat so that you can absorb vital nutrients. Food is broken down mechanically - through chewing, for example, and through the use of enzymes - into the form of molecules that can be absorbed by and moved through your blood. Your digestive system is made up of the following organs, in order:

  • Mouth
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine
  • Anus

The digestive system is assisted in its task by other important organs, including your liver, gallbladder and pancreas.

2. Our mouths secrete approximately one liter of saliva a day.

Saliva production through our salivary glands is the first step in digestion. Saliva is predominantly made up of water, but does contain other substances, and can be stimulated by just thinking about or smelling food. Food breakdown begins in our mouths through the process of chewing, and through enzymes present in saliva. Saliva both lubricates food for easy passage into the esophagus, and coats the food to protect our teeth and the lining of our mouth and esophagus.

3. It takes anywhere from two to five seconds for food to make its way down your esophagus into your stomach.

After we've chewed our food, it's formed into something called a bolus. Swallowing is a complex procedure in which the bolus is moved into the pharynx, the larynx (the organ connected to our windpipe) is covered, and the esophagus opening is widened to accept the bolus. The bolus is then moved down through the esophagus through coordinated muscle movements known as peristalsis.

The esophagus is bound on each end by a sphincter muscle, which is responsible for opening to allow the bolus to pass through. Heartburn can occur when the lower sphincter fails to close completely, allowing stomach acid to travel upward and irritate the tissue in the esophagus and throat.

4. Your stomach produces hydrochloric acid, the same stuff that masons use to clean bricks.

Luckily, our stomachs are lined by a thick layer of mucus to protect us from the acid and the enzyme pepsin that it produces. The mixing motion of the stomach, along with the acid and the breakdown of protein by the pepsin, turns the bolus into a liquid substance called chyme, which in turn is then slowly released into the small intestine. For a full meal, this process takes approximately two to three hours.

Only a few things are absorbed into the bloodstream at the level of the stomach, and interestingly, these are the very things that can cause stomach irritation: alcohol, aspirin and non-steroidal anti-inflammatory drugs (NSAIDs).

5. Your pancreas and liver are not mysterious organs: the primary role of each is to produce substances that break down the foods you eat.

As the chyme makes its way into your small intestine, it's met with juices produced by the liver and the pancreas. The liver produces bile, which is stored in the gallbladder and then released into the small intestine to break down fats, while the pancreas secretes enzymes into the small intestine that break down protein, carbohydrates and fats. The pancreas also releases a substance called bicarb that neutralizes any acid that's made its way out of the stomach.

6. Your small intestine is responsible for almost all of the absorption of nutrients from the foods we eat.

The small intestine is where the most important work of digestion takes place, that of further breaking down the food we eat into molecular components that can be absorbed into the bloodstream. You may remember from high school biology that the small intestine has three parts: the duodenum, the jejunum and the ileum. Bile from the gallbladder, and digestive enzymes from the pancreas, are mixed into the chyme in the duodenum. The final breakdown and absorption of nutrients occurs in the second two parts.

Absorption of nutrients is conducted by microscopic projections along the lining of the small intestine called villi. Celiac disease is a disorder in which the ingestion of gluten results in damage to the villi, which in turn can lead to health problems stemming from the lack of absorption of vital nutrients.

7. Fiber is what's left over when all the other parts of food have been digested.

Once the small intestine has completed its breakdown of food and absorption of nutrients, it propels the undigested parts of plant food, known as fiber, into the large intestine. Fiber is classified into two general types: soluble, which dissolves in water, and insoluble, which does not. Fiber both softens and bulks up the stool, and is essential for both digestive and overall health.

8. Your large intestine receives about one quart of liquid a day from the small intestine.

In addition to fiber, the small intestine propels liquid into your large intestine, where it's absorbed and stools are formed. The large intestine is made up of the ascending colon, the transverse colon, the descending colon, the sigmoid colon, and the rectum. Although there's great variation in frequency, the stool is in general moved once or twice a day into the rectum in preparation for a bowel movement.

9. Your GI system plays host to more than 500 species of bacteria.

We are not born with any bacteria in our digestive systems, but develop a significant population within the first month, most of which can be found in our large intestine. Recognition of the role that bacteria play in digestive health has stimulated booming sales of products containing probiotics, often labeled as "friendly bacteria." Bacteria fight off disease-carrying organisms, play a role in absorbing nutrients that slip past the small intestine through fermentation, and help to support our immune systems. You're most acutely aware of the work of bacteria when its process of fermentation causes you to experience intestinal gas.

Small intestine bacterial overgrowth (SIBO) is a health condition in which too many bacteria are present in the small intestine. SIBO has been theorized as a possible factor in the development of IBS for some individuals.

10. Your digestive system has its own little "mini-brain."

The functioning of the digestive system is regulated by the enteric nervous system (ENS), which is made up of a tremendous amount of nerve cells and is regulated by the same neurotransmitters, most notably serotonin, found in the brain. This similarity has earned the ENS the title of the "Second Brain".

Your brain and digestive system work in close partnership, a phenomenon that you have first-hand knowledge of any time your stomach flips when you think of something anxiety-provoking — or more dramatically if you experience diarrhea when you are stressed. This collaboration is thought to be essential to our survival as a species; although digestion is essential for life, dealing with threats is just as necessary. The body developed the "flight or fight" system to divert resources away from the digestive system to the systems of the body needed to fight off or run away from things that might do us harm. Dysfunction in the brain-gut connection has been theorized to play a role in the development of functional gastrointestinal disorders (FGDs).

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