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Absorption of Digested Products

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Absorption of Digested Products - Lesson Summary

The food is broken down into simpler molecules and absorbed in different parts of the alimentary canal, but maximum absorption occurs in the villi of the small intestine. These digested nutrients are absorbed into the blood and lymph to transport it throughout the body.
Absorption takes place in the intestinal mucosa, through passive transport and active transport. 

In passive transport, there is no expenditure of energy. There are three types of passive transport – simple diffusion, facilitated transport and osmosis that assist in absorption. Small amounts of glucose, amino acids and electrolytes are generally absorbed from a high concentration medium to a low concentration medium by simple diffusion. Fructose and some amino acids are absorbed down a concentration gradient with the help of a specific carrier protein through facilitated diffusion.

On the other hand, transport of water takes place from a dilute to a concentrated medium through osmosis. Absorption of nutrients such as sodium ions, glucose, galactose and amino acids take place against the concentration gradient through active transport which is much quicker and requires energy.

Unlike carbohydrates and proteins, fats are not absorbed through the intestinal villi. Fats are first acted upon by bile salts to form small, spherical droplets called micelles which can easily move through the intestinal mucosa. As micelles enter the intestinal mucosa, they are coated with protein to form chylomicrons, which are transported through lacteals in the villi. These lymph vessels ultimately release the absorbed substances into the bloodstream.
Besides the small intestine, drugs are absorbed in the mouth, simple sugars and alcohol are absorbed in the stomach wall, minerals such as potassium and sodium and drugs are absorbed in the large intestine. These absorbed nutrients are transported to different tissues of the body through the blood vessels. This process is called assimilation.
However, the digestive wastes pass through the large intestine, where water is absorbed and waste is solidified into faeces, which finally is eliminated through the anus.
If the food is infected, it causes intestinal infections by helminth worms or inflammation of the intestinal tract due to bacterial or viral infections. If the food is not properly digested, it leads to indigestion, constipation, vomiting and diarrhoea. 


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