11. When not needed for immediate use, the bile is stored up in a sac called the gall-bladder.
12. The pancreas is a gland which lies just back of the stomach. It makes pancreatic juice.
13. The spleen is found near the pancreas.
14. There are five important digestive organs—the mouth, the stomach, the intestines, the liver, and the pancreas.
15. There are five digestive fluids—saliva, gastric juice, intestinal juice, bile, and pancreatic juice.
DIGESTION OF A MOUTHFUL OF BREAD.
1. Let us suppose that we have eaten a mouthful of bread, and can watch it as it goes through all the different processes of digestion.
2. Mastication.—First, we chew or masticate the food with the teeth. We use the tongue to move the food from one side of the mouth to the other, and to keep the food between the teeth.
3. Mouth Digestion.—While the bread is being chewed, the saliva is mixed with it and acts upon it. The saliva moistens and softens the food so that it can be easily swallowed and readily acted upon by the other digestive juices. You have noticed that if you chew a bit of hard bread a few minutes it becomes sweet. This is because the saliva changes some of the starch of the food into sugar.
4. After we have chewed the food, we swallow it, and it passes down through the oesophagus into the stomach.
5. Stomach Digestion.—As soon as the morsel of food enters the stomach, the gastric juice begins to flow out of the little glands in which it is formed. This mingles with the food and digests another portion which the saliva has not acted upon. While this is being done, the stomach keeps working the food much as a baker kneads dough. This is done to mix the gastric juice with the food.
6. After an hour or two the stomach squeezes the food so hard that a little of it, which has been digested by the gastric juice and the saliva, escapes through the lower opening, the pylorus, of which we have already learned. As the action of the stomach continues, more of the digested food escapes, until all that has been properly acted upon has passed out.
7. Intestinal Digestion.—We sometimes eat butter with bread, or take some other form of fat in our food. This is not acted upon by the saliva or the gastric juice. When food passes out of the stomach into the small intestine, a large quantity of bile is at once poured upon it. This bile has been made beforehand by the liver and stored up in the gall-bladder. The bile helps to digest fats, which the saliva and the gastric juice cannot digest.
8. The pancreatic juice does the same kind of work that is done by the saliva, the gastric juice, and the bile. It also finishes up the work done by these fluids. It is one of the most important of all the digestive juices.