A coiled tube, representing the longest section of the gut, averaging between 6 to 7 meters in length (19.7 to 23 feet), with an opening of 1 inch in diameter. Within this tube, the final stages of digestion and most absorption take place. Here carbohydrates, fats and proteins are broken down into smaller molecules, which along with vitamins, minerals and water, are able to cross the intestinal lining and walls of the blood vessels to enter the blood. Efficient absorption is accomplished by the tremendous surface area of the intestine. Not only is the intestine long, and coiled together to fit within the abdomen, but the inner surface contains many folds and ridges. In addition, the entire inner surface is covered with tiny fingerlike projections called villi. In addition, these villi are covered with even tinier fingerlike projections called microvilli! All of these structures are supplied with capillaries providing a massive surface for absorption. If the small intestine was just a long coiled tube, it would have a surface area of 4 square yards. Pretty big, eh? Not when you consider that the folds, ridges, villi and microvilli produce a surface area of more than 250 square yards! That's larger than a tennis court!

The small intestine is composed of three sections...

Duodenum
The first, shortest, and widest section of the small intestine, averaging about 25 cm long (9.8 inches), and almost entirely fixed to the posterior body wall. The duodenum is the only section of the small intestine that is somewhat adhered to the body wall. Food from the stomach enters the duodenum through the pyloric sphincter. The bile and pancreatic ducts empty into the duodenum as well. The bile duct supplies bile from the gull bladder and liver, and the pancreatic duct supplies digestive enzymes from the pancreas.

The duodenum is the second most common location for ulcers in the digestive tract. 5 million Americans deal with ulcers of either the stomach or duodenum every year. 10% of Americans experience ulcers at some point in their lives. They are caused by a bacterial infection. The bacteria, along with the natural enzymes from the gut, eat away at the protective lining in the duodenum, causing an open sore on the duodenum interior. Stress increases stomach acid, which flows into the duodenum and increases vulnerability to duodenal ulcers. Taking aspirin, or nonsteroidal anti-inflammatory drugs over a long period of time can increase stomach acidity and ulcer vulnerability. Steroids, genetics and alcohol can also increase your risk. Smoking not only increases your risk, but also prevents the healing of ulcers once they form! Dark green leafy vegetables such as spinach can help prevent digestive problems. Blacks and Latinos are twice as likely to develop ulcers than are Whites.

Jejunum
The second section of the small intestine, measuring about 2.4 to 2.8 meters (7.9 to 9.23 inches). It is often empty, and generally thicker, more vascularized and thus more red than the ileum. Most of the jejunum lies central around the umbilicus (belly button). The inner mucus membrane is deeply folded for more absorbing surface area than the ileum. Both the jejunum and ileum are suspended from the posterior body wall by a thin vascularized two-layer membrane called the mesentery.

Ileum
The third, final and longest section of the small intestine, averaging about 3.6 to 4.2 meters in length (11.8 to 13.8 inches). Most of the ileum lies below the jejunum just above the level of the genitals and a slightly to your right side. Contents of the jejunum empty into the cecum (the first part of the large intestine).

• You consume 30 tons of food throughout your life.
• It takes 24 hours to completely digest food.
• The digestive tube from your mouth to your anus is 9 meters or 30 feet long.
• The digestive system has a surface area of 2000 square feet.
• The surface area of the digestive system is approximately equal to that of a single's tennis court!
• The average person eats 3 lbs. of food daily.
• Vomiting can empty the stomach along with the first foot of intestines.
• Water molecules in the gut can move at 1500 miles/hour due to peristalsis.
• It takes 4 to 8 seconds for food to travel to the stomach.
• Most absorption occurs within the first quarter of the small intestine.
• The small intestine averages 21 feet long.
• The bacteria as it naturally exists within the lumen (or hollow space) of the digestive tract is perfectly harmless and beneficial, helping the digestion and absorption of food that otherwise couldn't be absorbed. However, if this bacteria ever did enter the body and the blood, due to a ruptured digestive organ, it could be extremely harmful and even lethal.
• The lumen (contents) of the digestive tract is considered outside the body like the hole of a donut, since it's continuous with the outside of the body. The lungs and kidneys eliminate most of the waste products from inside the body. The digestive tract is disqualified from this function, since most contents of feces never technically enters the body.

Nutrition
Fiber

Digestion

Other digestive organs
Mouth
Pharynx
Esophagus
Stomach
Large intestine
Rectum
Anal canal

Glands involved in digestion
Liver
Gall bladder
Pancreas