As soon as you see think of a delicious sandwich, your mouth seems to look watery!

Have you ever thought of the mechanisms that every food needs to undergo after entering our body?

Soon after the consumption of food, a series of actions takes place within the body. It enters the digestive tract, where the complicated process of digestion and absorption takes place. I, being a Nutritionist, just wanted showcase this tedious process in a simple way so that every one can understand. Let’s see the biochemical changes taking place in the gastro intestinal tract, after consuming a sandwich.

Digestive system


The gastrointestinal tract of the body comprises of mouth, stomach, small intestine and large intestine. The digestion if any food begins from the chewing process in the mouth. Soon after the food is chewed it is swallowed so that the food reaches the stomach. The digestion of carbohydrate starts in the mouth by the action of the salivary amylase enzyme present in the saliva. The salivary amylase enzyme breaks down the starch present in the bread and the peanut butter into simpler carbohydrates. The vegetables consist of fiber which is first crushed by teeth, and then its nutrients are acted upon by the digestive enzymes in the stomach.


Soon after the sandwich reaches the stomach the chewed food is collected in the stomach and subjected to churning by mixing with gastric juices. The stomach acid that is secreted as a result of hunger sensation mixes with gastric juices and this inactivates the salivary enzyme. Proteins from bread and peanut butter begin to uncoil when they mix with gastric acid, making them available to the gastric protease enzymes that begin to digest proteins. Fat present in the butter forms a layer on top of the watery mixture.


Sugars from the bread require very little digestion that they begin to traverse the intestinal cells immediately on contact. Pancreatic enzymes act upon the starch in the small intestine. Starch is broken down by these enzymes to simpler fragments so that they can be absorbed across the intestinal walls. Fat from butter is emulsified with the watery digestive fluids by bile. The pancreatic and intestinal lipases act on fats and convert them into smaller particles so as to be absorbed easily by the intestinal mucosa.

The protease enzymes act on the proteins and similarly smaller protein fragments are developed which is then absorbed in to the blood. Vitamins and minerals do not undergo any digestion process. It is liberated from other nutrients during the digestive process and directly absorbed in to the intestinal cells.


Large intestine is solely responsible for re-absorption and elimination. Fluids and some of the minerals are absorbed here. Some of the soluble fibers present in the bread and vegetables that have undergone the digestion process are partially digested by the bacteria living in the large intestine. The products of digestion are absorbed. Most of the fibers escape digestion, pass through the large intestine and are excreted as feces. This shows the binding effect of fibers by making the cholesterol and minerals to be excreted along with them.


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