Almost all animals have a tube-type digestive system in which:
- food enters the mouth,
- passes through a long tube,
- and exits as feces (poop) through the anus.
- During the process of absorption, nutrients that come from the food (including carbohydrates, proteins, fats, vitamins, and minerals) pass through channels in the intestinal wall and into the bloodstream. The blood works to distribute these nutrients to the rest of the body. The waste parts of food that the body can’t use are passed out of the body as feces.
- Every morsel of food we eat has to be broken down into nutrients that can be absorbed by the body, which is why it takes hours to fully digest food.
- At the end of the esophagus, a muscular ring called a sphincter (pronounced: sfink-ter) allows food to enter the stomach and then squeezes shut to keep food or fluid from flowing back up into the esophagus.
- The stomach muscles churn and mix the food with acids and enzymes, breaking it into much smaller, more digestible pieces.
- An acidic environment is needed for the digestion that takes place in the stomach. Glands in the stomach lining produce about 3 quarts of these digestive juices each day.
- Most substances in the food we eat need further digestion and must travel into the intestine before being absorbed. When it’s empty, an adult’s stomach has a volume of one fifth of a cup, but it can expand to hold more than 8 cups of food after a large meal.
- By the time food is ready to leave the stomach, it has been processed into a thick liquid called chyme (pronounced: kime). A walnut-sized muscular tube at the outlet of the stomach called the pylorus (pronounced: py-lore-us) keeps chyme in the stomach until it reaches the right consistency to pass into the small intestine.
- Chyme is then squirted down into the small intestine, where digestion of food continues so the body can absorb the nutrients into the bloodstream.
The Small Intestine
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 body.
The liver (located 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 still important for healthy digestion.
- pancreas produces enzymes that help digest proteins, fats, and carbohydrates. It also makes a substance that neutralizes stomach acid.
- liver produces bile, which helps the body absorb fat. The liver also plays a major role in the handling and processing of nutrients. These nutrients are carried to the liver in the blood from the small intestine.
- Bile is stored in the gallbladder until it is needed. These enzymes and bile travel through special channels (called ducts) directly into the small intestine, where they help to break down food.
The Large Intestine
- From the small intestine, food that has not been digested (and some water) travels to the large intestine through a 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 function is to remove water from the undigested matter and form solid waste that can be excreted. The large intestine is made up of three parts:
- The cecum (pronounced: see-kum) is a pouch at the beginning of the large intestine that joins the small intestine to the large intestine. This transition area allows food to travel from the small intestine to the large intestine. The appendix, a small, hollow, finger-like pouch, hangs off the cecum. The appendix (which is so often removed these days, is the actual storage for “good” bacteria for the gut). Nowadays the appendix is removed at an early age and most people without an appendix can vouch for Intestinal problems (Gut problems). It is extremely useful for 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 transverse colon, which absorb water 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.
Learn more about the body through the Basic Informative Manual – Check it out
In humans, protein must be broken down into amino acids,
- starches into simple sugars,
- and fats into fatty acids and glycerol.
- The digestive system is made up of the alimentary canal / digestive tract and
- the other abdominal organs that play a part in digestion, such as the liver and pancreas. The alimentary canal (also called the digestive tract) is the long tube of organs – including the esophagus, the stomach, and the intestines – that runs from the mouth to the anus. An adult’s digestive tract is about 30 feet long.