After the absorption of the nutrients in the small intestine, the 1.5 m long large intestine absorbs water from the remaining undigested food and converts it into a solid mass. The solid mass of waste matter is stored in the lowermost part of the large intestine, the rectum, and is then excreted as ‘stools’ through the anus.
The function of the small intestine is to digest the food into simpler nutrients, and to absorb these nutrients. If food stays longer in the small intestine, it will have more time to get digested completely and will also enable the body to absorb all the nutrients. The very long length (more than 6 m) of the small intestine enables the food to stay there longer. The finger-like ‘intestinal villi’ on the inner wall of the small intestine help in absorbing the nutrients in the bloodstream. The liver and pancreas produce enzymes that travel to the small intestine to help break down proteins, fats, and carbohydrates into sugar. This process is known as metabolism.
After the food has been chewed and mixed with saliva, it reaches the stomach through the oesophagus. The food is prepared for actual digestion in the small intestine, which is connected to the large intestine, and ends in the rectum. The undigested remains of the food and urine are excreted from the body. We can survive without water only for a few days, but the body can manage without food for quite some time. If the starvation goes on for a very long time, the body becomes weak and prone to diseases.
Organs are parts of the body having specific tasks. An example is the intestine, in which food is broken down and the nutrients are absorbed in the blood. Another important organ is the liver, which utilizes the components of food. Other organs are the kidneys, the spleen, the heart, and our biggest organ, the skin. They are all made up of different kinds of tissues, such as muscular tissue, fatty or supportive tissue, and blood vessels. The tissue in each organ is specifically designed to perform the tasks assigned to that organ. Thus, the muscular tissue of the heart is different and performs different functions as compared to that in the upper thigh. Each organ interacts with other organs to keep the body healthy.
The different cells of our body have very different tasks, but they are all similar in their structure. They have a cell wall or a cell membrane, which protects the inner matter of the cell and controls what goes in the cell and what comes out of it. The nucleus inside the cell controls all the processes in the cell. The energy for these processes comes from mitochondria, the power house of the cell. They are responsible for cell respiration. The endoplasmic reticulum takes care of the conversion of substances and for detoxifying the cells. All these organelles are embedded in the liquid cytoplasm inside the cell. If we drink less fluid, the cytoplasm will dry out and the cell may die.
When we breathe, the oxygen reaches our lungs via the mouth, nose, and trachea. The lungs have a number of very tiny cavities known as air sacs which are covered by a network of very fine blood vessels. An exchange of gases takes place here. Impure blood reaches these capillaries and releases the waste gas carbon dioxide in the air sacs. This is exhaled out of the body, and freshly inhaled oxygen is absorbed into the air sacs. This oxygen is released into the blood via the capillaries.
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