What happens to the food after it is swallowed?

After the food has been chewed and mixed with saliva, it reaches the stomach through the esophagus. 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.

Why is the small intestine so long?

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 then 6 m) of the small intestine enables the food to stay there longer. The finger-line '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 knows as metabolism.

What does the large intestine do?

After the absorption of the nutrients the small intestine, the 1.5 m long large intestine absorbs water from the remaining undigested food and converts in 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.