CH-16 (DIGESTION AND ABSORPTION) BIOLOGY CLASS-XI, NCERT Topper Notes

Chapter-16
Digestion and Absorption

Points to Remember

Digestion :The process in alimentary canal by which yhe complex food in converted mechanically and biochemically into simple substances suitable for absorption and assimilation in the body of animals/ organisms.

Food : A substances which is taken and digested in the body to provide material for growth, repair & energy for reproduction and resistance from disease or regulation of body processes.

Thecodont : The teeth embedded in the sockets of the jaw bone e.g., in mammals.

Diphyodont : The teeth formed twice in life e.g., in mammals.

Heterodont : Different types of teeth. An adult human has 32 permanent teeth which are of four different types.

Peristalsis : The involuntary movement of the gut by which the food bolus is pushed forward.

Deglutition : The process of swalloing of food bolus. It is partly voluntary and partly involuntary.

Ruminants : The herbivours animals (e.g., cow, buffalo etc.) which have symbiotic bacteria in the rumen of their stomach, which synthesize enzymes to hydrolyse cellulose into monosaccharides.

Diarrhoea : The abnormal frequent discharge of semisolid or fluid faecal matter from the bowel.

Vomiting : The ejection of stomach contents through the mouth, caused by antiperistalsis.

Dysentery : Frequent watery stools often with blood and mucus, along with pain, fever and causes dehydration.

Chyme : The semifluid mass, into which food is converted by gastric secretion, which passes from the stomach into the small intestine.

Gastric : Anything associated with stomach is given a prefix 'gastric'.

Proenzyme : The inactive forms of enzymes.

Sphincter : A flap like structure at various junctions pf the alimentary canal which facilites one way traffic (movement of material) in the alimentary canal.

Bolus : The masticated food mixed with saliva.

Hepatic : Anything associated witb liver is given a prefix 'hepatic'.

Goblet cells :The cell of intestinal mucosal epithelium which secrete mucus.

Glisson's capsule : The connective tissue sheath which covers the hepatic lobules of liver.

Hepatic lobules : The structural and functional units of liver containing hepatic cells which are arranged in the form of cords.

Sphincter of Oddi : The sphincter which guard the opening of common hepatopancreatic duct.

Villi : The small finger-like folding in the small inyestine which increase the surface area for absroption of digested food.

Crypta of Lieberkuhn - Pits of intestine/ tubular intestinal glands.

Succus entericus - Intestinal juicea, secreted in small intestine.

Basic Steps of Holozoic Nutrition :

(1) Ingeation : Intake of food.

(2) Digeation : Breaking down of complex organic food matrials into simpler, smaller water soluble molecules.

(3) Absorption and assimilation : Absorption of digeated food into blood or lymph and ita use in the body cells for aynthesis of complex components.

(4) Egeation : Elmination of udigested food as faeces :

Digeative glands :

(A) Salivary gland - 3 types are (1) Parotids (cheek) (ii) Sublinguals (Below the tongue) (iii) Submaxillaru or submandibular (lower jaw) Secrete saliva which contains ptyalin (Salivary Amylase).

(B) Pancreas : A dual gland that secretes pancreatic juice and also secretes Hormines. Located between limbs of U shaped duodenum.

(C) Liver : In abdominal cavity (1.2-1.5kg.)

2 lobed → Hepatic lobules → Hepatic cells (arranged as cords) → Secrete bile → Goes to hepatic ducts → bile stored in gall bladder.

ABSORPTION OF FATS

• Fatty acids and monoglycerides and Glycerol (insoluble).


• Micelles (t8ny spheres w8th hydroph8lic ends) formed.


• Absorbed by epithelial cells of small intestine (simple diffusion).


• Chylomicrons transported into lymph vessels (lacteals) in the villi.


• Lymph vessels release the absorbed substances into bloodstream.


• Malnutrition - When a person is not getting enough food or getting unbal-anced diet.

PEM - Protein Energy Malnutrition :

Symptoms :

Cure :

Calorific Value : Amount of heat energy released by 1 gm of substrate after complete oxidation.

Calorific value of Carbohydrates is 4.1 k.cal/g = 17.1 kj/g

Protein is 5.6 keal/g = 23.4 kj/gm

Fats is 9.4 kcal/g (app) = 39.2 kj/gm