16.3 ABSORPTION OF DIGESTED PRODUCTS

16.3 ABSORPTION OF DIGESTED PRODUCTS 

  • Absorption is the process by which the end products of digestion pass through the intestinal mucosa into the blood or lymph. 
  • It is carried out by passive, active or facilitated transport mechanisms. 
  • Small amounts of monosaccharides like glucose, amino acids and some electrolytes like chloride ions are generally absorbed by simple diffusion. 
  • The passage of these substances into the blood depends upon the concentration gradients. 
  • However, some substances like glucose and amino acids are absorbed with the help of carrier proteins. This mechanism is called the facilitated transport.
  • Transport of water depends upon the osmotic gradient. 
  • Active transport occurs against the concentration gradient and hence requires energy. 
  • Various nutrients like amino acids, monosaccharides like glucose, electrolytes like Na+ are absorbed into the blood by Active transport mechanism. 
  • Fatty acids and glycerol being insoluble, cannot be absorbed into the blood. 
  • They are first incorporated into small droplets called micelles which move into the intestinal mucosa. 
  • They are re-formed into very small protein coated fat globules called the chylomicrons which are transported into the lymph vessels (lacteals) in the villi. 
  • These lymph vessels ultimately release the absorbed substances into the blood stream. 
Molecules
Mode of transport
Glucose, amino-acids and some electrolytes like chloride ions (Cl-)
Absorbed by simple diffusion
Glucose (Glut-1 to 4), fructose (Glut-5) and amino acids
Facilitated transport (carrier proteins)
Glucose, electrolytes like Na+
Active transport
Water
Osmotic gradient
Fatty acids and Glycerol
Micelles> Chylomicrons> Lymph vessels (lacteals)
  • Absorption of substances takes place in different parts of the alimentary canal, like mouth, stomach, small intestine and large intestine. 
  • However, maximum absorption occurs in the small intestine. 
  • A summary of absorption (sites of absorption and substances absorbed) is given in Table 16.1. 
NCERT Class XI Biology: Chapter 16 - Digestion And Absorption ...

  • Assimilation: The absorbed substances finally reach the tissues which utilise them for their activities, this process is called assimilation. 
  • The digestive wastes, solidified into coherent faeces in the rectum initiate a neural reflex causing an urge or desire for its removal. 
  • The egestion of faeces to the outside through the anal opening (defaecation) is a voluntary process and is carried out by a mass peristaltic movement.

16.4 DISORDERS OF DIGESTIVE SYSTEM 
  • The inflammation of the intestinal tract is the most common ailment due to bacterial or viral infections. 
  • The infections are also caused by the parasites of the intestine like tapeworm, roundworm, threadworm, hookworm, pin worm, etc. 
  • Jaundice: The liver is affected, skin and eyes turn yellow due to the deposit of bile pigments. 
  • Vomiting: It is the ejection of stomach contents through the mouth. This reflex action is controlled by the vomit centre in the medulla. A feeling of nausea precedes vomiting. 
  • Diarrhoea: The abnormal frequency of bowel movement and increased liquidity of the faecal discharge is known as diarrhoea. It reduces the absorption of food. 
  • Constipation: In constipation, the faeces are retained within the rectum as the bowel movements occur irregularly. 
  • Indigestion: In this condition, the food is not properly digested leading to a feeling of fullness. The causes of indigestion are inadequate enzyme secretion, anxiety, food poisoning, over eating, and spicy food.

Comments

  1. Unknown25 August 2020 at 03:39

    Really helpful sir....
    Ur student from thamarai Nik.

    ReplyDelete
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    1. Unknown25 August 2020 at 03:55

      This comment has been removed by the author.

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  2. Oly13 October 2020 at 07:51

    thank you sir it helps a lot

    ReplyDelete

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