Human Digestive System | How the food is digested in our body ?
Human Digestive System
We will discuss today about the human digestive system because every time when you take food this simple question arises that How the food is digested in our body ?
So, let’s start…
The nutrition in human beings takes place through human digestive system. The human digestive system consists of the alimentary canal and its associated glands. The various organs of the human digestive system in sequence are :
- Oesophagus (or Food pipe),
- Small intestine and
- Large intestine.
The glands which are associated with the human digestive system and form a part of the human digestive system are :
- Salivary glands,
- Liver and
We can describe the whole in 5 steps —
1. Ingestion –
In human beings, food is ingested through the mouth.
The salivary glands in our mouth produce saliva. Our tongue helps in mixing this saliva with food. Saliva is a watery liquid so it wets the food in our mouth. The wetted food can be swallowed more easily. The salivary glands help in chemical digestion by secreting enzymes. The human saliva contains an enzyme called salivary amylase which digests the starch present in food into sugar.
- The slightly digested food in the mouth is swallowed by the tongue and goes down to stomach through the food pipe called oesophagus. The food is churned in the stomach for about three hours. During this time, the food breaks down into still smaller pieces and forms a semi-solid paste. From the stomach, the partially digested food enters the small intestine.
- The small intestine is the largest part of the alimentary canal. The small intestine in human beings is the site of complete digestion of food (like carbohydrates, proteins and fats). It receives the secretions of two glands: liver and pancreas
- Liver secretes bile. Bile is a greenish yellow liquid made in the liver which is normally stored in the gall bladder. Bile is alkaline and contains salts which help to emulsify or break the fats (or lipids) present in the food.
- Pancreas is a large gland which lies parallel to and beneath the stomach. Pancreas secretes pancreatic juice which contains digestive enzymes like pancreatic amylase, trypsin and lipase. The enzyme amylase breaks down the starch, the enzyme trypsin digests the proteins and the enzyme lipase breaks down the emulsified fats.
3. Absorption –
The small intestine is the main region for the absorption of digested food. After digestion, the molecules of food become so small that they can pass through the walls of the small intestine (which contain blood capillaries) and go into our blood. The inner surface of small intestine has millions of tiny, finger-like projections called villi. The presence of villi gives the inner walls of the small intestine a very large surface area. And the large surface area of small intestine helps in the rapid absorption of digested food. The digested food which is absorbed through the walls of the small intestine, goes into our blood.
4. Assimilation –
The blood carries digested and dissolved food to all the parts of the body where it becomes assimilated as part of the cells. This assimilated food is used by the body cells for obtaining energy as well as for growth and repair of the body. The energy is released by the oxidation of assimilated food in the cells during respiration. The digested food which is not used by our body immediately is stored in the liver in the form of a carbohydrate called glycogen. This stored glycogen can be used as a source of energy by the body as and when required.
5. Egestion –
A part of the food which we eat cannot be digested by our body, this undigested food cannot be absorbed in the small intestine. So, the undigested food passes from the small intestine into a wider tube called large intestine. The walls of large intestine absorb most of the water from the undigested food with the help of villi. Undigested food is passed out (or egested) from our body through anus.