The human body is among the many wonders of this world. Each part of the body is a marvel by itself and the way the parts work together in a coordinated manner is nothing short of a miracle. Scientists have been amazed at the secrets embedded in the human body and they have been engaged in research to unravel the myriad functions, processes and characteristics of every part.
Most living beings need oxygen and food. The cardiopulmonary system, which helps us breathe in life-sustaining oxygen and pumps it to all parts of the body, is the most significant part of the human body. Equally important is the digestive system which nourishes the body.
Scientists have long said that no life can exist in this world without the cardiopulmonary and the digestive systems.
They also say that we can learn about the lungs, which are at the centre of the respiratory system, by examining them and monitoring their functions. Similarly one can learn with a great deal of clarity about the kidneys, ears, eyes and nose.
But the digestive system is different. Over the years, scientists have been able to unravel much about how the stomach, which is at the centre of the system, works. Yet, there is a lot more hidden. The more the researchers scan the system, the more the secrets keep tumbling out.
This series is your magic key to unlock the secrets of the digestive system and learn how it absorbs food and helps nourish the body.
We learn about how we walk, talk, listen, see, touch and taste by studying the parts of the body that are involved in these actions. Some of these parts function constantly without respite, but some parts work only when necessary.
For instance, the legs are at rest when we are not walking and the eyes do not have to work when we close them.
However, the heart, lungs, kidneys and the stomach work without rest every second, right from the moment of birth to the time of death.
If some of these organs are damaged or start malfunctioning, their functions can be replicated by machines such as the heart-lung machine or the dialysis machine used in case of kidney failure. But the digestive and other processes of the stomach can never be taken over by a machine.
We assume that we are giving the stomach a day off when we undertake a fast for religious or other reasons. But the truth is that the stomach keeps itself busy every minute of the day and night.
The digestive system begins as a tube in the throat and is linked to the mouth. As it descends inside the body it takes on various shapes and functions. It processes the food we eat, absorbs the nutrients and sends out the waste. Its length is seven times your height.
It is made up of ten parts:
- Gall Bladder
- Small Intestine
- Large Intestine
Learning about the digestive system and how it works will help us regulate our eating and other lifestyle habits and ensure a healthy life for us. So, read on. Enjoy learning about yourself, and in the process, I do hope you get to grips (no gripes!) with your tummy!
Nature provides human beings with whatever they need to live.
The respiratory system takes in oxygen from the air and releases carbon dioxide to sustain our life and keep us going. In a similar manner, the digestive system absorbs the nutritious content from the food we eat and the rest is pushed out as waste. The most important part of the digestive system is the stomach. Let us see how it functions.
When we see mother making dosas, our eyes and nose convey to the brain what they sense. Thus we are attracted by the smell of the dosa on the frying pan and the coconut and mint chutney that will be served with it. At the same time, the mouth starts to salivate and the stomach growls with the secretion of an acid and enzymes that help to digest food. The first step in the digestive process begins in the mouth. We use the teeth, jaw muscles and the tongue to chew, crush and push down the food we put into our mouth. An enzyme called amylase, found in the saliva, moistens our mouth and softens the food that we chew.
Once the food is crushed to the required extent, it is pushed down into the throat and then on to the stomach through the oesophagus. When the food moves down the throat, the windpipe is closed by a valve called the epiglottis. This is done to prevent the food from entering the windpipe.
Even as the food we chew starts to descend from the mouth, a nerve called the vagus signals to the stomach that it should be ready for its task. Within microseconds of getting the signal, the stomach starts to secrete hydrochloric acid to welcome the food particles coming down the oesophagus.
At this point, it is important to know why we should not go hungry for long hours. Whenever we are hungry the stomach secretes hydrochloric acid in anticipation of the food that is going to be eaten and sent down to it. When we do not eat anything, the hydrochloric acid in the stomach starts eating into the inner walls of the stomach and even the oesophagus. This acid can be dangerous.
The stomach processes food much like the grinders and blenders we use in our kitchens. When food reaches it, the stomach muscles tighten and start churning and grinding the food.
It does not matter if the food has been well chewed or half-chewed or whether it is a vegetarian or non-vegetarian dish. The stomach pulverises the food into a state that makes it ready for the next part of the digestive process.
The stomach usually takes three to four hours to process the food. Therefore, after you have eaten, it is advisable to wait three to four hours before you sit down for the next meal.
The process of absorption of nutrients starts when the food that has been made into a consistent paste by the stomach reaches the duodenum, which is the beginning of the small intestine.
This is where the liver and the pancreas swing into action. The bile secreted by the liver and the pancreatic juice, a mixture of enzymes secreted by the pancreas, break the food particles down into smaller pieces to help the small intestine absorb them.
The bile and the pancreatic juice flow into the small intestine. In fact it is the bile that flows out of the liver first. Some of the enzymes in the bile trigger the pancreas into secreting the pancreatic juices. Then the two liquids flow into the small intestine and start their work.
When the food mixes with the bile, it bubbles up into a foam which breaks down and absorbs the fat and oil in the food. The fatty content of the food we eat cannot be absorbed or digested if the liver does not secrete its bile.
After the food is digested, the body does not waste the bile. The salts that form an important part of the bile are absorbed by the small intestine.
Many of my patients think that bile is secreted by the gall bladder, because the Tamil name for the gall bladder is bile bag. They turn pale at the prospect of having their gall bladders removed and start thinking of a life without the power to digest food.
The truth is, the gall bladder is only a storage organ for the bile on its way from the liver to the intestine. Removal of this organ does not have any harmful effect whatsoever. On the other hand, the operation often saves a life, and the presence of stones indicates a diseased organ with little or no function.
In a similar manner, the enzymes secreted by the pancreas break down the carbohydrates, proteins and fatty substances into smaller pieces that can be absorbed by the small intestine.
The walls of the small intestine are covered with millions of fingerlike projections called villi. These villi help the small intestine to absorb the smaller pieces of the food particles. Beneath the villi cells are very tiny blood vessels which carry the absorbed nutrients to various parts of the body.
From the small intestine the food moves on into the large intestine. The small intestine is one and a half inches wide while the large intestine is three inches wide. But the small intestine is longer than the large intestine and stretches to between 20 and 25 feet.
A human being can survive if his large intestine is removed. But no one can live without the small intestine because it is here that the food we eat is absorbed into the body, giving us the energy and nourishment we need. We will deal later with the small intestines, their functioning and the enzymes they secrete.
So far we have seen how the food we put into our mouth travels down to the stomach and through the small and the large intestines. From the large intestine, what remains of the food after all the nutrients have been absorbed in the small intestine is excreted through the anus.
If there is a problem at any stage during the movement of the food from the mouth to the anus, it can be dangerous for us.
For instance, if a part of the intestine malfunctions, or if the pancreatic juice starts seeping into the other parts of the body, then it could well mean disaster for the hapless owner of the said set of digestive organs. Shocking isn’t it? Yes, the pancreatic juice, which is secreted to help digest the food we eat, is even more poisonous than a snake’s venom, with the power to eat through all in its path. But more of that later!
(Watch out for this space; more stuff will be added here every Wednesday.)