Your Table of Contents Part 2 - Food Digestion Control Valves
Whatever you eat and drink is passed down along the food digestion canal by a sort of a “milking” process, known technically as peristalsis. It is accomplished by contractions of the digestive tube above the mass of food and simultaneous relaxations of that part of the tube below the food mass. The contractions are made possible by the existence of a well developed layer of circular muscle fibers in the wall of this tube we call the food digestion canal. These particular muscles differ from the ones you have in your arm and leg. They are muscles over which you have no control. They contract and relax without consulting you and without your aid. In fact, there is a constant wave of such contractions and relaxations starting at the upper end of the food digestion canal every few minutes. This wave passes onward and downward throughout the rest of the canal in accordance with a definite slow, steady rhythm of its own.
From what I have said, you will readily understand that once started on its onward passage through the food digestion canal, the food eaten, unless delayed along the way, would pass through the entire intestinal tract in a matter of a very short space of time. If it did so, the digestive secretions would not have time to do their work. Digestion, the breaking down of foodstuffs into easily absorbable substances, takes time. Absorption, the actual taking into your blood stream and body of the food substances which have thus been made suitable for use, also takes time. These procedures cannot be hurried. The food digestion canal does not like “shortcuts” even though its owner may!
To make sure that we take the “time out” for the very necessary periods of digestion and absorption, Nature has devised a way of making the trip down the alimentary canal on a local train that makes all the stops. By strengthening the circular muscular fibers in some parts of the digestive canal so that they are strong enough to hold back the food mass despite the onward urge of peristalsis these stops are accomplished. This ring-like group of muscles then acts as a valve in the tube and is known as a sphincter. It acts in exactly the same way as the diaphragm on your camera does. By opening and shutting it controls the size of the tube and thus impedes or permits the passage of material along the canal.
It is normal, therefore, for the food to be halted for very definite purposes in its onward journey at several places along the thirty-two feet of the food digestion canal. In contrast, in a person whose digestive system is disordered, the usual action of the sphincters is interfered with. When interference occurs the food mass is allowed to pass on in an imperfectly digested state. This causes much disturbance to the lower part of the food digestion canal and a corresponding amount of distress to the person who owns it. In such a situation the gravy train has become an express, skips the stations and runs through the red lights. Trouble results. It is known as stomach problems or intestinal trouble, depending upon which area suffers the most disorder.
There are other instances in which these sphincters or valves become over-active and instead of permitting the food mass to travel on at the right time, hold it back. The result is that the food mass remains abnormally long in a certain area. Then as more food comes down and more digestive secretions are added by the glands, the traffic piles up behind this over-active sphincter. Since this sphincteric valve doesn’t work, the food digestion canal above this point becomes greatly distended and the person very uncomfortable.
Most people are aware of only one sphincter, the terminal one, but there are many others. As long as we are blessed with good digestion, in other words, normal functioning of the intestinal tract, this is the only one we are ever aware of. But when health takes a holiday, certain others make their presence felt. If you will look at the accompanying image, you will see that the first of these, although a rather weak one, is at the place where the gullet joins the stomach. Sometimes spasm occurs at this point and food has difficulty in passing through the gullet into the stomach. Fortunately, this condition is not too common. Doctors know it under the term of cardiospasm.
When it occurs one gets the feeling that food has not actually entered the stomach. Frequently much water is drunk in an attempt to wash “the lump” on into the stomach. Even with this assistance the food is not infrequently brought up again, sometimes hours after eating. A pain or a burning or heaviness is often experienced under the lower end of the breast bone. The condition is usually brought on by swallowing some highly irritating substance, though it may be completely nervous in its origin. Of one thing you may be sure. It is a problem which you would be smart not to try to solve by yourself. Nowhere is the motto “see your doctor” more apt than in this situation.
Far more frequently the thick, circular muscle at the lower end of the stomach, known as the pylorus, is subject to disorder. This sphincter normally delays the passage of the food mass in its passage through that portion of the food digestion canal known as the stomach until the stomach digestive juices have had time to accomplish their part of the digestive process. The pylorus holds the food here until it is thoroughly dissolved and mixed with these gastric juices. It becomes a thick, soupy, definitely acid mixture, one of the digestive juices being hydrochloric acid.
When the acidity has reached a certain point, it somehow presses a chemical button which relaxes the sphincter or pyloric valve. This permits the food to be passed on into the small intestine for further digestion. Curiously enough, when sufficient of this partially digested mixture has passed into the intestines, the same acidity pushes another chemical button with a quite different result; namely, it causes the closing of the pyloric sphincter or valve.
Assuming that matters have gone along normally so far, we become aware of the action of another small circular muscle or sphincter. It is in the bile duct, a muscular tube which connects the liver to the intestine. Ordinarily this sphincter is contracted.