Theory:

 The small intestine:
 
It is a very long tube about seven metres in length. Here the food is mixed with bile juice, pancreatic juice and intestinal juice. These juices help in completing the digestion. At the end of digestion, carbohydrates are broken down into glucose and fructose, proteins into amino acids and fats into fatty acids and glycerol.
 
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Liver:
 
The liver is a reddish-brown gland situated in the upper part of the abdomen on the right side. It is the largest gland in the body. It secretes bile juice that stored in a sac called the gall bladder. The bile plays an important role in the digestion of fats. The pancreas is a large cream coloured gland located just below the stomach. The partly digested food now reaches the lower part of the small intestine where the digestion completion takes place.
 
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Absorption:
 
The digested food can now pass into the blood vessels in the wall of the intestine. This process is called, absorption. The inner walls of the small intestine have thousands of finger-like outgrowths called, villi. The villi increase the surface area of the intestine for absorption of the digested food.
 
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Assimilation:
 
The absorbed substances transported through the blood vessels to different organs of the body, where these substances are used to build complex substances such as the proteins for the body. This process is called, assimilation.
 
(5) Large intestine:
 
It is called a large intestine because of the diameter (width); it is much wider than the small intestine, but also much shorter. It is about 1.5 metre in length and helps in absorbing water. It is the place for temporary storage of undigested food. The process of digestion does not take place here. It absorbs water and some salts from the undigested food material. The remaining waste passes into the rectum and remains there as semi-solid faeces.
 
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(6) Anus:
 
It is the last part of human digestive system. The faecal matter is removed through the anus from time-to-time. This is called, egestion (or) excretion.
  
Peristalsis:
Food in the digestive system moves from the oesophagus to the anus by rhythmic contraction and expansion of the wall of the digestive system. This movement is called, peristalsis.
 
Below is a flow chart of the process of digestion:
 
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Interesting facts:

  • When glucose is taken in, it instantly breaks down in the cell with the help of oxygen, which provides instant energy to the organism. Glucose does not need digestion; it is directly absorbed into the blood.
  • Sometime you may have experienced the need to pass watery stool frequently. This condition is known as diarrhea. It may be caused by an infection, food poisoning or indigestion. It can be fatal in a few cases. Even before a doctor is consulted, the patient should be given plenty of boiled and cooled water with a pinch of salt and sugar dissolved in it. This process is called, Oral Rehydration Salt (ORS).
Reference:
Small intestine: https://visualsonline.cancer.gov/details.cfm?imageid=4364
Liver:https://commons.wikimedia.org/wiki/File:Blausen_0428_Gallbladder-Liver-Pancreas_Location.png
Villi in small intestine:https://www.uzdevumi.lv/p/biologija/9-klase/gremosana-7974/re-071636bb-9ce6-4739-83e5-01ffa9eaf793
Large intestine:https://commons.wikimedia.org/wiki/File:Blausen_0604_LargeIntestine2.png