Digestion and AbsorptionNEET Zoology · Class 11 · NCERT Chapter 16

You can expect 1 to 2 questions from Digestion and Absorption in NEET 2027. The most reliable scoring areas are: the dental formula (2123/2123), the enzyme produced at each stage of digestion, the site where each nutrient is absorbed, how fats are absorbed via chylomicrons and lacteals, and the two protein energy malnutrition disorders (marasmus and kwashiorkor).

The human dental formula is 2123/2123, which means 2 incisors, 1 canine, 2 premolars and 3 molars in each half of each jaw. This gives 8 teeth in each half and 32 teeth in total. Human teeth are thecodont (set in sockets), diphyodont (two sets in a lifetime: milk teeth and permanent teeth) and heterodont (different types for different functions).

Pancreatic juice contains five main enzymes. Trypsin and chymotrypsin are proteases that break proteins and polypeptides into smaller peptides. Carboxypeptidase further breaks peptides into amino acids. Pancreatic amylase breaks starch into maltose. Pancreatic lipase breaks fats (triglycerides) into fatty acids and glycerol. Nucleases break nucleic acids into nucleotides. Trypsin is secreted as inactive trypsinogen and activated by enterokinase from the intestinal mucosa.

Succus entericus is the intestinal juice secreted by the inner lining of the small intestine. It contains maltase (breaks maltose into glucose), lactase (breaks lactose into glucose and galactose), sucrase (breaks sucrose into glucose and fructose), peptidases (break dipeptides into amino acids), lipases (break fats), and nucleotidases (break nucleotides). Together with pancreatic juice, these enzymes complete the digestion of carbohydrates, proteins, fats and nucleic acids.

Carbohydrates (as glucose, galactose, fructose) and amino acids are absorbed through the villi of the small intestine and enter the blood capillaries directly. They travel to the liver via the hepatic portal vein. Fats, however, are absorbed as fatty acids and glycerol, which are reassembled into triglycerides inside the intestinal cells, then packaged into lipoprotein droplets called chylomicrons. Chylomicrons enter the lymph capillaries called lacteals inside each villus. They reach the bloodstream through the thoracic duct, bypassing the liver.

Both are forms of protein energy malnutrition (PEM) most common in young children. Marasmus results from a severe shortage of both calories and protein, causing extreme wasting of muscle and fat, very low body weight and a wizened appearance. Kwashiorkor results from enough calories but very little protein, causing oedema (swelling due to fluid retention), a pot belly, skin and hair changes, and growth failure. The key distinguishing point: marasmus = deficiency of both protein and calories; kwashiorkor = protein deficiency with adequate calories.

The stomach has four regions. The cardiac region is near the entry of the oesophagus. The fundic region is the upper dome-shaped part. The body (main body) is the largest middle region. The pyloric region connects to the duodenum and contains the pyloric sphincter. The gastric glands in the body and fundus secrete pepsinogen (converted to pepsin by HCl), HCl, rennin (in infants, for milk protein coagulation), and mucus. Mucus protects the stomach wall from HCl.