Explain process of absorption of digested food

Most of the absorption of digested food takes place in the small intestine. The inner lining of the small intestine has millions of tiny finger-like projections called the villi. These projections increase the surface area of the small intestine for more efficient food  absorption. Within these villi, the capillaries absorb nutrients from the digested products of proteins and carbohydrates and lead them into the blood stream.

Following are the mechanisms of absorption of various nutrients, minerals and water:

    • Simple diffusion − Glucose, amino acid, electrolytes such as Cl− follow this method; depends upon concentration gradient

    • Facilitated transport − Fructose and some amino acids are absorbed by this method. Absorption occurs with the help of carrier ion such as Na+.

    • Active transport − Glucose, some amino acids, Na+ follow this method. Absorption is against concentration gradient. Thus, it requires energy.

    • Fatty acids are insoluble; hence first broken into small droplets called micelle, which further reform into small protein-coated fat globule called chylomicron (in intestinal mucosa), which are then transported into lacteals in villi, which finally release them into blood stream.

  • Substances absorbed in mouth − Certain drugs are absorbed in blood capillaries, lining lower parts of tongue.

  • Substances absorbed in stomach − water, simple sugars, alcohol

  • Substances absorbed in small intestine − almost all nutrients
    Maximum absorption occurs here.

  • Substances absorbed in large intestine − water, minerals, drugs

  • Absorbed substances finally reach tissues where they are utilized. This process is called assimilation.

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Complex components of food such as carbohydrates are broken down into simpler substances and are then utilized by the body. This process of breaking down of complex substances into simpler substances is known as digestion.The human digestive system consists of a number of organs, each performing a different function.  



In the digestive system, food first enters the buccal cavity. The buccal cavity consists of teeth and the tongue. Apart from the tongue and the teeth, the buccal cavity also has salivary glands, which secrete saliva. The enzymes present in saliva breakdown the fats or digest the starch present in the food we eat. The swallowed food passes into the oesophagus from the mouth. The oesophagus or the food pipe runs along the neck and chest. The walls of the food pipe move to push the food down into the stomach. After the food pipe, the food enters the stomach. The stomach is a thin-walled bag. It is flattened, U-shaped, and is the widest part of the alimentary canal. It opens into the small intestine. The inner lining of the stomach secretes hydrochloric acid, mucous, and digestive juices. The mucus secreted by the stomach protects the inner lining of the stomach. The hydrochloric acid secreted by the stomach kills the bacteria that enter the stomach through food. It also makes the medium of the stomach acidic. The digestive juices secreted by the stomach take part in the process of digestion by breaking down the food into smaller substances. The stomach empties its contents into the small intestine. The small intestine is a highly coiled, tube-like structure. It is about 7.5 metres in length. It receives secretions from the liver and the pancreas in the form of bile and pancreatic juice. Apart from this, the wall of the small intestine also secretes juices. When the partly digested food reaches the small intestine, the juices secreted by the small intestine complete the process of digestion. Nutrients from the digested food pass into blood vessels, which are present in the walls of the small intestine. This process is known as absorption. From the small intestine, the food is passed on to the large intestine where the water and remaining salts gets absorbed. The remaining waste material then enters the rectum. It is stored there in the form of semi-solid faeces. The faecal material is finally removed from the body through the anus. This process is known as egestion.

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