Most of theabsorption of digested foodtakes place in thesmall intestine.The inner lining of the small intestine has millions of tiny finger-like projections called thevilli. 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 nutrientsMaximum absorption occurs here.
Substances absorbed in large intestine water, minerals, drugs
Absorbed substances finally reach tissues where they are utilized. This process is calledassimilation.
