How come the stomach digests everything that we eat, but it does not digest itself? Luckily for us, a living stomach has ways to protect itself from itself! To carry it through a day's meals, the stomach produces about six cups of digestive juices. A key ingredient of this digestive juice is extremely corrosive hydrochloric acid. Drop some zinc into a cup of digestive juice, and the acid would gradually dissolve the metal. (Which isn't surprising if you've ever been sick and vomited: that burning in your throat is caused by acid ejected from your stomach). In spite of carrying such a vicious reagent in our stomachs, how do we remain unharmed?
To get our answer, let's first understand -
a) What does the stomach do?
The stomach as you know is a part of our digestive system. It has been assigned the duty of breaking down the food that we eat into simpler forms. After this, the food goes into the intestines to be absorbed by the body to give us energy.
b) How does the stomach break down the food?
This is accomplished with the help of the contractions of the muscles and some digestive juices. These juices called gastric juices are produced within the stomach. The food chewed and swallowed by us, reaches the stomach. Here it mixes with the gastric juices and gets digested.
What is gastric juice?
Gastric juice or gastric acid is the digestive juice secreted by the lining of our stomachs. It is mainly composed of hydrochloric acid, 2 protein digesting enzymes (pepsin and rennin) and mucus. The enzymes are relatively harmless, but hydrochloric acid is extremely strong and can dissolve tissue in hours. Mucus is a protective slime. All these are secreted by special types of cells present in the lining of the stomach called epithelial cells. Of the epithelial cells lining the stomach, the majority are mucous glands.
What does the trick?
Just as human beings use fire, the body has evolved ways to harness useful-but-threatening chemicals without harming itself. The stomach lining not only produces the acid, fluids, and other chemicals needed to break down the food you eat, it also produces special cells to protect itself from being digested. The epithelial cells which secrete mucus protect the stomach from the acid.
They act in two ways.
Firstly, the stomach's lining of epithelial cells continuously regenerate themselves and are replaced every three days. So cells underneath remain protected from the harsh environment of the churning stomach sac.
Secondly, mucus made by the epithelial cells forms a thick lining on the inner stomach wall and acts as a barrier for the stomach lining against noxious acid. While stomach juices eat through, mucus is continuously replenished. An empty stomach can weigh 1 pound or more and 38% of this is slippery mucus.
Now the question arises--Can this lining never be breached? It can sometimes, when the body's defenses fail. Then the underlying tissue can indeed be damaged as the acid tries to digest it. This can make painful sores in the stomach wall called ulcers.
So eat good food and help your stomach in protecting itself and keeping you healthy.