4: Digestion

Have you ever seen a Venus flytrap? This strange plant grows in many places. It is called a flytrap because each of its leaves is something like a steel-trap, to use to catch flies.

When a fly touches the leaf, the trap shuts up at once, and the poor fly is caught and can­not get away. The harder it tries to escape, the more tightly the trap closes upon it, until after a time it is crushed to death.

But we have yet to learn the amazing thing about this strange plant, which seems to act so much like an animal. If we open the leaf after a few days, it will be found that the fly has almost entirely disappeared. The fly has not escaped, but a fluid formed inside of the trap, has dissolved it, and the plant has absorbed a portion of the fly. In fact, it has really eaten it.

The process by which our food is dissolved and changed so that it can be absorbed to nourish the body, is called digestion (di-ges'-tion).

The Venus flytrap has a very simple way of digesting its food. Its remarkable little trap serves it as a mouth to catch and hold its food, and as a stomach to digest it. The ar­rangement by which our food is digested is more complicated. Let us study the different parts by which this wonderful work is done.

The Digestive Tube: Most of the work of digesting our food is done in a long tube within the body, called the digestive tube or canal.

This tube is twentyfive or thirty feet long in a full-grown man; but it is so coiled up and folded away that it takes little space. It begins at the mouth, and ends at the lower part of the trunk. Most of it is coiled up in the abdomen.

The Mouth: The space between the upper and the lower jaw is called the mouth. The lips form the front part and the cheeks the sides. At the back part are three openings. One, the upper, leads into the nose.

There are two lower openings. One of these leads into the stomach, and the other leads to the lungs. There is a special valve there that closes the tube that leads to the lungs when we swallow food or drink, so our food or drink does not go into our lungs.  The back part of the mouth joins the two tubes, which lead from the mouth to the lungs and the stomach, and is called the throat. The mouth contains the tongue and the teeth.

The Teeth: The first teeth, those which come when we are small children, are called tem­porary or baby teeth. We lose these teeth as the jaws get larger and the second, or per­manent, teeth take their place. There are twenty teeth in the first set, and thirty-two in the second. Very old persons sometimes have a third set of teeth. They buy them, and they are called ‘dentures’.

The Salivary (sal'-i-vary) Glands: There are three pairs of salivary glands. They form a fluid called the saliva (sa-li' -va). It is this fluid which moistens the mouth at all times. When we eat or taste something that we like, the salivary glands make so much saliva that we sometimes say the mouth waters. One pair of the salivary glands is at the back part of the lower jaw, in front of the ears. The other two pairs of glands are placed at the underside of the mouth. The saliva produced by the salivary glands is sent into the mouth through little tubes called ducts.

The Gullet: At the back part of the throat begins a narrow tube, which passes down to the stomach. This tube is about nine inches long. It is called the gullet, food pipe, or esopha­gus (e-soph'-a-gus).

The Stomach: At the lower end of the esophagus the digestive tube becomes enlarged, and has a shape somewhat like a pear. This is the stomach. In a full-grown person the stomach is large enough to hold about three pints.

At each end of the stomach is a narrow opening so arranged that it can be opened or tightly closed, as may be necessary. The upper opening allows the food to go into the stomach, the lower one allows it to go out into the intestines. This opening is called the pylorus (py-Io' -rus), or gatekeeper, because it closes so as to keep the food in the stomach until it is ready to go out.

In the membrane which lines the stomach there are many little pocket-like glands, in which a fluid called the gastric juice is formed. This fluid is one of the most important of all the fluids formed in the digestive canal.

The Intestine (in-tes'-tine) At the lower end of the stomach the digestive canal becomes narrow again. This narrow portion, called the intestine, is about twenty-five feet long in a grown person. The last few feet of the intestine is larger than the rest and is called the colon. This long tube is coiled up and snugly packed away in the abdomen. In the membrane lining the intestines are to be found little glands, which make a fluid called intestinal juice.

The Liver: Close up under the ribs, on the right side of the body, is a large brown-colored organ, called the liver. The liver is about half as large as the head, and is shaped so as to fit snugly into its comer of the abdomen. The main digestive business of the liver is to make fluid called bile, which is very necessary for the digestion of our food.

The bile is a bitter fluid of a golden-brown color. It is carried to the intestine by means of a little tube or duct, which enters the small intestine a few inches below the stomach. When the bile is made faster than it is needed for immediate use, it is stored up in a little pear-shaped sac called the gallbladder, which hangs from the underside of the liver.

The liver is a very wonderful organ and does many useful things besides making bile. Basically the liver is sort of a blood filter. It aids in various ways in digesting the food, it helps to keep the blood that passes through it pure by removing from it harmful substances which are formed within the body or that come in with our food or drink.

The Pancreas (pan'-cre-as) The pancreas is another large and very important gland which is found close to the stomach, lying just behind it in the abdominal cavity. The pancreas forms a fluid called the pancreatic juice, which enters the small intestine at nearly the same place as the bile. The pancreas also makes insulin, a special hormone that allows sugar to get into our cells, where it is used for energy.

The Spleen: Close to the pancreas, at the left side of the body, is a dark, roundish organ about the size of the fist, called the spleen. It is not known that the spleen has much to do the work of digestion, but it is so closely connected with the digestive organs that we need to know about it. It has special work to do in making blood cells.

There are five important organs of digestion; the mouth, the stomach, the intestines, the pancreas, and the liver. There are five digestive fluids; saliva, gastric juice, bile, pancreatic juice, and intestinal juice.

We can see that the process that changes our food into substances that our body can use to build and repair itself is very complicated. We need to know how we can best help it to do this job well. =^..^=

Questions:

1. Have you ever had a ‘sour-stomach’ or a stomach ache from something you ate? We call this ‘indigestion’.

2. Did you know that part of our digestion begins in the mouth? This is why we need to chew our food carefully.

Divider

Cat

NEXT

CONTENTS

 

Logo