Before the food you eat can do its job, it has to be absorbed by all the minute cells in your body. First, it has to be broken down so that it will dissolve. This process is called digestion and it takes place as the food travels through your digestive tract. The dissolved food then passes into your bloodstream and is carried to all the different parts of your body.
Your digestive tract is a long tube which winds from your mouth to your anus (back passage). Most of your digestive organs are in your abdomen. This is separated from your chest by a large sheet of muscle called the diaphragm.
The Digestive Process
Here’s how the food goes through the digestive process:
1. Your teeth bite and chew the food into small pieces. Saliva (spit), made by the salivary glands, moistens it so it slides down your throat more easily. Saliva contains the first digestive enzyme. This starts digesting starch. (Your salivary glands swell up when you have mumps).
2. The muscles of your tongue force the food back into your throat (pharynx) and your throat muscles guide it into your gullet (esophagus). As you swallow, a flap called epiglottis blocks off the top of the nearby windpipe so the food does not “go down the wrong hole” and make you choke.
3. The food goes down your esophagus into your stomach. It does not slide down by gravity but is pushed along by muscles in the esophagus. This process is called peristalsis and takes place all along your digestive tract. The sound you hear when your “stomach” rumbles is food and air being mixed up and pushed through the tract. In theory, peristalsis means that you could still eat and drink if you were standing on your head.
4. In your stomach the food is churned about and mixed with stomach juice. This contains enzymes which start digesting protein. It also contains hydrochloric acid, which helps to kill any bacteria swallowed with the food. A meal stays in your stomach for about four hours.
5. Your liver has several important jobs. One of these is to make a green liquid called bile. This acts rather like a detergent. It breaks up the fats you eat into tiny drops so that enzymes can work on them. Bile is stored in your gall bladder…
6. One of the jobs of thepancreas is to make a juice containing many different digestive enzymes. These work on all types of food.
7. The coiled small intestine is only about 4cm in diameter but it is about four meters long. In the first part, called the duodenum, the food is mixed with bile from your liver and with the juice from your pancreas.
8. By the time it gets to the second part of your small intestine (the ileum), most of the food is digested. It passes through the walls of the intestine into your blood. Your blood then carries the digested food to your liver for more processing before taking it round your body.
9. Water and any food which cannot be digested move on into your large intestine. Most of the water passes into your blood through the walls of the first part of the large intestine (the colon). Some of the water passes out of your body later as urine.
10. The more solid waste matter, called feces, is stored further along your large intestine (in the rectum). The muscles of your rectum push it out through your anus when you go to the toilet.
How food gets into your blood?
The inner wall of the ileum is covered with thousands of tiny structures called villi which stick out like fingers. These give the tube a huge surface area for absorbing the food. The walls of the villi are only one cell thick. The digested food passes through them and into the tiny blood vessels inside. The digested fats do not go directly into the blood vessels. They are absorbed into special “lymph” vessels and enter the blood later.
Is Appendix useful to humans?
The appendix has no function in humans, though in animals which eat grass it plays a part in digestion. An inflamed appendix (appendicitis) has to be taken out or it may burst and spread infection right through the abdomen.
Chemical changes are taking place in your body all the time. These are speeded up by enzymes, which are special proteins made in your cells. There are several thousand different sorts of enzyme. Digestive enzymes help to break down and dissolve your food.
Illnesses associated with food digestion
You are sick when your diaphragm muscle and the muscles in the wall of your abdomen contract strongly and force partly digested food back up out of your stomach. It is the stomach juice which makes vomit taste sour. There are many reasons for being sick, including eating too much, eating food that has gone bad and drinking too much alcohol.
Diarrhea is often caused by an infection in the intestines or by food poisoning. Food travels through the intestines so fast that the water cannot be absorbed properly. If you have diarrhea, you should drink extra fluid to make up for what you are losing. Constipation is often caused by not eating enough fiber.