Our digestive system is made up of the body parts that change raw food into nutrients that the body can use and waste. It also moves the nutrients and waste through our body. It is made up of the mouth including the teeth, jaws, tongue and salivary glands, esophagus, stomach, liver, gall bladder, bile duct, pancreas, pancreatic duct, small intestine including the duodenum, jujenum and ileum, large intestine, rectum and anus.
The Mouth: When a person eats any food such as an apple, digestion starts when the jaws use the teeth to bite into the apple. This begins to break down the food by dividing it into bite sized pieces. Then the teeth and jaws chew the apple to break the bite sized pieces into smaller pieces. This is to make the pieces small enough to fit through the esophagus and to make less work for the stomach. While the food is still in the mouth, the salivary glands produce saliva containing an enzyme which starts off the digestive process.
The food is then swallowed which takes the food from the mouth to the esophagus. The esophagus is the tube that connects the mouth to the stomach. Food moves through the esophagus by peristalsis, which is a wave of muscle contractions that pushes the food down the tube.
At the end of the esophagus is the lower esophageal sphincter(LES), which closes to prevent food from re-entering the esophagus.
Sometimes, when something gets in the stomach that the stomach doesnít like, the stomach muscles contract and force anything that is in your stomach up through the lower esophageal sphincter. The LES is trying to stay closed but the contractions create more pressure than your LES can hold. When this happens, the stomach contents go back up through the esophagus and come out through the mouth. We call this "throwing up".
After food has left the esophagus it enters the stomach. The stomach provides four basic functions that assist in the early stages of digestion and prepare the food for further processing in the small intestine:
The liver has hundreds of functions. One of its main functions is to process fat and other nutrient-rich liquefied food that drains from the small intestine so it can be used. Another important function of the liver is that it produces sugars from proteins and fatty substances; and it secretes albumin which helps to keep fluid within the blood vessels.
The liver also converts poisons in the blood into materials which can be safely excreted from the body. The liver uses calcium to reduce the amount of acid in the body waste. This allows us to go to the bathroom without pain or body damage.
It also secretes bile which is a substance containing fatty materials. These help in the digestion, as well as the absorption of fatty products.
The Gall Bladder:
The gall bladder is a pouch-shaped organ which lies near the liver. It accepts bile from the liver, and stores it. When food is digested, the gallbladder releases bile into the small intestine where it is able to help dissolve fats.
The pancreas makes and delivers digestive juices through a tube called the pancreatic duct to the upper part of the small intestine.
The Small Intestine:
The small intestine is approximately 20 feet long and is divided into 3 segments - the duodenum, jejunum, and ileum.
The duodenum begins just beyond the stomach and curves around the head of the pancreas and the entrance of the common bile duct, in a C-shaped formation. At the spot where the stomach and duodenum meet, is a muscle called the pyloric sphincter which prevents the regurgitation of material back into the stomach. The duodenum is responsible for further processing the material from the stomach (called chyme), by secreting enzymes which aid in digestion. Bile and pancreatic juice also enter the duodenum around its midpoint, and by moving the chyme in a shaking kind of motion, the duodenum mixes the chyme with these enzymes within its lumen, further aiding digestion.
The jejunum is the next portion of the small intestine, and it has a lining which is specialized in the absorption of carbohydrates and proteins. The proteins have been broken down in the stomach by enzymes called pepsin and acid into amino acids. The carbohydrates are broken down in the duodenum by enzymes from the pancreas and liver into sugars. Fats are broken down in the duodenum by "lipase" from the pancreas into fatty acids. Amino acid, sugar, fatty acid particles, vitamins, minerals, electrolytes and water are small enough to soak into the villi of the jejunum and drop into the blood stream. The blood takes all these nutrients to all the other parts of the body to provide fuel to do their jobs.
The ileum is the last portion of the small intestine, and it is responsible for absorption of fats, and bile salts which are a component of bile. The pores in the ileum are slightly bigger than those in the jejunum and allow vitamin B12, vitamins dissolved in fatty liquids, electrolytes, bile salts and water to soak through the walls and into the blood stream.
Where the ileum joins the large intestine is a valve, called the ileocecal valve, which prevents the back flow of materials into the small intestine. By the time material reaches this point, it has a rather pasty consistency.
The Large Intestine:
The parts of the food that canít be digested get pushed into the large intestine, also called the colon. It is about 5 feet long. Its function is to move the waste from the small intestine on to the rectum. The material first passes through the ascending colon and then through the transverse colon. Throughout this process, it absorbs more water. By the time the waste reaches the segment called the sigmoid, it is quite firm. The sigmoid colon is designed to slow down this movement of the waste until it is ready to be eliminated.
The lowermost segment of the large intestine is called the rectum. It stores the firm waste until you are ready to get rid of it by "going to the bathroom". It has a specialized muscle, called the anal sphincter, which prevents the body waste from escaping until the appropriate time.