The small intestine is made up of three parts:
- the duodenum (pronounced: due-uh-DEE-num), the C-shaped first part
- the jejunum (pronounced: jih-JU-num), the coiled midsection
- the ileum (pronounced: IH-lee-um), the final section that leads into the large intestine
The inner wall of the small intestine is covered with millions of microscopic, finger-like projections called villi (pronounced: VIH-lie). The villi are the vehicles through which nutrients can be absorbed into the blood. The blood then brings these nutrients to the rest of the body.
The liver (under the ribcage in the right upper part of the abdomen), the gallbladder (hidden just below the liver), and the pancreas (beneath the stomach) are not part of the alimentary canal, but these organs are essential to digestion.
The liver makes bile, which helps the body absorb fat. Bile is stored in the gallbladder until it is needed. The pancreas makes enzymes that help digest proteins, fats, and carbs. It also makes a substance that neutralizes stomach acid. These enzymes and bile travel through special pathways (called ducts) into the small intestine, where they help to break down food. The liver also helps process nutrients in the bloodstream.
From the small intestine, undigested food (and some water) travels to the large intestine through a muscular ring or valve that prevents food from returning to the small intestine. By the time food reaches the large intestine, the work of absorbing nutrients is nearly finished.
The large intestine's main job is to remove water from the undigested matter and form solid waste (poop) to be excreted.
The large intestine has three parts:
- The cecum (pronounced: SEE-kum) is the beginning of the large intestine. The appendix, a small, hollow, finger-like pouch, hangs at the end of the cecum. Scientists believe the appendix is left over from a previous time in human evolution. It no longer appears to be useful to the digestive process.
- The colon extends from the cecum up the right side of the abdomen, across the upper abdomen, and then down the left side of the abdomen, finally connecting to the rectum.
The colon has three parts: the ascending colon and the transverse colon, which absorb fluids and salts; and the descending colon, which holds the resulting waste. Bacteria in the colon help to digest the remaining food products. - The rectum is where feces are stored until they leave the digestive system through the anus as a bowel movement.
It takes hours for our bodies to fully digest food.
