CONTEST ENTRY: Favourite Topic of Science

Hello Steemians, greetings from India...
This is my first post in this community. This is my ENTRY for the contest FAVOURITE TOPIC OF SCIENCE.

So my favourite topic of science during my school days was the digestive system and human nutrition. Even today, I can relate to it while I have some stomach complications or someone in my family does. As I took up engineering in graduation, the learning never materialized much, but I am happy to participate in this contest and write about it to you.

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Human beings are heterotrophic, i.e. they cannot prepare their own food like plants do. They depend on other living organisms, plants to derive energy. Further, the mode of nutrition in human beings is holozoic. This means the food is ingested as a whole and processing of the ingested food takes place inside the human body.

Now let's understand the human digestive system and the processes involved in human nutrition.

The various steps of nutrition in human beings are ---

• INGESTION
• DIGESTION
• ABSORPTION
• ASSIMILATION
• EGESTION

INGESTION: This is the process of eating food, i.e. physically putting food into the mouth with the help of hands.

DIGESTION: The process of digestion begins in the mouth itself.

The ingested food is acted upon by teeth, tongue and salivary glands in the mouth or buccal cavity. The teeth cuts, tears and grinds the food into smaller pieces. The saliva produced in salivary glands moistens the food

while the salivary amylase enzyme in saliva initiates chemical digestion. The tongue then mixes the food and saliva properly and pushes the food paste into the oesophagus.

The oesophagus (also known as the food-pipe) carries the swallowed food to the stomach by an alternate contraction and expansion movement called 'peristalsis'.

In stomach, the food matter is processed for about 3 hours, where it is acted upon by gastric juice, turning it into a semi-solid paste.

The semi-digested food then enters into small intestine from stomach. This is regulated by the 'sphincter muscle'.

The small intestine happens to be the largest part of the alimentary canal and is about 6.5 m long in an adult man. Being narrow, it is called the small intestine despite its length. It is positioned in a coiled form.

Food (carbohydrates, proteins, fats) is completely digested in the small intestine. The liver and pancreas secretion also acts upon the food matter in the small intestine.

Liver secretes bile juice. It is stored in the gall bladder.

Pancreas secrete pancreatic juice.

The walls of small intestine contains glands secrete intestinal intestinal juice containing a number of enzymes. This completes the digestion of complex carbohydrates into glucose, proteins into amino acids, fats into fatty acids and glycerol.

In this way, complex food matter are broken down into simpler form by the process of digestion.

ABSORPTION: After digestion, the food molecules become so small that they can easily pass through the walls of the small intestine and go into the blood stream. This is called absorption. This takes place with the help of small finger like projections called villi present on the inner wall lining of the small intestine.

ASSIMILATION: The blood carries digested and dissolved food to all parts of the body where the different human processes utilizes them. The remaining undigested food matter cannot be absorbed and goes down further into the alimentary canal and enters the Large Intestine. Most of the water content of the undigested food matter is absorbed in the large intestine. So this undigested matter becomes solid.

EGESTION: The undigested solid matter is stored in rectum of the large intestine for some time before the body excretes it out through anus.

^{Original art by author}

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This is just a note on human nutrition and human digestive system for normal understanding. It is not meant for any exam preparation or higher studies. However readers may use this article for their use at their own risk.

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Reference:

Source 1

Source 2

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