The large intestine's main job is to remove water from the undigested matter and form solid waste poop to be excreted. Reviewed by: Larissa Hirsch, MD. Larger text size Large text size Regular text size. What Is the Digestive System? Almost all animals have a tube-type digestive system in which food: enters the mouth passes through a long tube exits the body as feces poop through the anus Along the way, food is broken down into tiny molecules so that the body can absorb nutrients it needs: Protein must be broken down into amino acids.
Starches break down into simple sugars. Fats break down into into fatty acids and glycerol. The waste parts of food that the body can't use are what leave the body as feces.
How Does Digestion Work? 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 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.
Fiber is undigestible and moves through the digestive tract without being broken down by enzymes. Many foods contain both soluble and insoluble fiber. Soluble fiber dissolves easily in water and takes on a soft, gel-like texture in the intestines. Insoluble fiber, on the other hand, passes essentially unchanged through the intestines.
Foods such as meat, eggs, and beans consist of giant molecules of protein that must be digested by enzymes before they can be used to build and repair body tissues. An enzyme in the juice of the stomach starts the digestion of swallowed protein.
Then in the small intestine, several enzymes from the pancreatic juice and the lining of the intestine complete the breakdown of huge protein molecules into small molecules called amino acids.
These small molecules can be absorbed through the small intestine into the blood and then be carried to all parts of the body to build the walls and other parts of cells.
Fat molecules are a rich source of energy for the body. The first step in digestion of a fat such as butter is to dissolve it into the watery content of the intestine. The bile acids produced by the liver dissolve fat into tiny droplets and allow pancreatic and intestinal enzymes to break the large fat molecules into smaller ones.
Some of these small molecules are fatty acids and cholesterol. The bile acids combine with the fatty acids and cholesterol and help these molecules move into the cells of the mucosa. In these cells the small molecules are formed back into large ones, most of which pass into vessels called lymphatics near the intestine. These small vessels carry the reformed fat to the veins of the chest, and the blood carries the fat to storage depots in different parts of the body.
Another vital part of food that is absorbed through the small intestine are vitamins. The two types of vitamins are classified by the fluid in which they can be dissolved: water-soluble vitamins all the B vitamins and vitamin C and fat-soluble vitamins vitamins A, D, E, and K.
Fat-soluble vitamins are stored in the liver and fatty tissue of the body, whereas water-soluble vitamins are not easily stored and excess amounts are flushed out in the urine.
Water and salt. Most of the material absorbed through the small intestine is water in which salt is dissolved. The salt and water come from the food and liquid you swallow and the juices secreted by the many digestive glands.
The major hormones that control the functions of the digestive system are produced and released by cells in the mucosa of the stomach and small intestine. These hormones are released into the blood of the digestive tract, travel back to the heart and through the arteries, and return to the digestive system where they stimulate digestive juices and cause organ movement. Both of these hormones work on the brain to help regulate the intake of food for energy.
Together, nerves, hormones, the blood, and the organs of the digestive system conduct the complex tasks of digesting and absorbing nutrients from the foods and liquids you consume each day. Search temple health. Your Digestive System. Why Is Digestion Important?
How Is Food Digested? Movement of food through the system. Production of digestive juices. Saliva also has a special chemical, called an enzyme, which starts breaking down carbohydrates into sugars. Once swallowed, muscular contractions of the oesophagus massage the ball of food down into the stomach. The food passes through a sphincter, or small muscle ring, into the stomach. Here it is mixed with gastric juices. The stomach is a muscular bag and it churns the food to help break it down mechanically as well as chemically.
The food is then squeezed through a second sphincter into the first part of the small intestine, called the duodenum. Once in the duodenum, the food is mixed with more digestive enzymes from the pancreas and bile from the liver. Food is then squeezed into the lower parts of the small intestine, called the jejunum and the ileum.
Nutrients are absorbed from the ileum, which is lined with millions of finger-like projections called villi. Each villus is connected to a mesh of capillaries. This is how nutrients pass into the bloodstream. The pancreas is one of the largest glands in the human body. As well as digestive juices, it secretes a hormone called insulin. Insulin helps to regulate the amount of sugar in the blood.
Diabetes is a condition caused by problems with insulin production. Any undigested food, such as fibre, is passed through the ileo-caecal valve to the large intestine. The incoming blood from the small intestine brings nutrients to the liver for processing, for example, glucose from the breakdown of food is brought to the liver and stored there as glycogen. Other nutrients brought to the liver include amino acids and glycerol.
Once the nutrients have been absorbed into the body from the small intestine, the remaining waste is passed into the large intestine also known as the colon.
The large intestine is made up of the caecum, ascending colon, transverse colon, descending colon and sigmoid colon and rectum. The appendix is attached to the caecum. Content from the small intestine comes into the large intestine as fluid and gradually becomes solid as water and salts are absorbed out as it travels through the large intestine by muscular waves called peristalsis Mucus is secreted to aid the passage of faeces to the rectum.
Stool, or faeces, are stored in the sigmoid colon until a bowel movement pushes them into the rectum and out of the body. Healthy human beings have roughly as many micro-organisms, such as bacteria, living in and on them as they do cells in their body trillions. The gut microbiome is the varied population of micro-organisms that live in your digestive system, lining the inside of your intestines. The highest concentration of micro-organisms in the human gut is in the large intestine.
Your microbiome is composed of many different species of bacteria. The more varied the species in your population, the healthier it is. The health of your gut microbiome is reflected in your general health. For example, some gut bacteria can bring about fermentation of undigested dietary fibre in the large intestine.
The fibre has made it through our digestive system that far without being digested, because as humans we lack the enzymes to digest it. But the bacteria have the necessary enzymes, fermenting the fibre to produce short-chain fatty acids, compounds which have a role in preventing some diseases and improving the gut barrier.
The bacteria of the large intestine can also synthesise vitamins that humans cannot produce themselves. Third edition Small intestine. Your digestive system and how it works updated Sept Cleveland Clinic. Digestive System. Skip to content. Salivary glands Digestion starts in the mouth, where salivary glands secrete saliva. Oesophagus Food in the mouth is swallowed and then pushed through the oesophagus by muscular contractions and relaxations called peristalsis until it reaches the lower oesophageal sphincter, which is a valve that controls food moving from the oesophagus into the stomach and stops it from refluxing back up the oesophagus.
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