# Physiology of Digestion for BSc and MSc students # composition and functions of saliva, gastric juice, bile, pancreatic juice and intestinal juice

1. Prepared by Dr. SHAMPA JAIN
Govt M. H. College Jabalpur

2. Digestion is process by which food substances are changed
physically and chemically. So that they are reduced to simple
assimilable forms.
 The stage of digestion comprises liquefying of food by the
mastication, swallowing, digestive juices and onward
movement of peristalsis is called mechanical digestion.
 Various enzymes present in digestive juices ,these enzymes
catalyzes the hydrolysis of protein, carbohydrates and
lipids. This is called chemical digestion.
 Digestive juices secreted in the various parts of alimentary canal
 Saliva in the mouth
 Gastric juice in the stomach
 Bile, pancreatic and intestinal juice in the duodenum

3.  Digestion in buccal cavity
 Secretion , composition and functions of saliva
 Saliva is secreted in the mouth by 3 pairs of salivary glands. It
consists of water (99%) , inorganic salts (0.2%)- NaCl,
KCl,CaCO3 and Na2HPO4,mucus and enzymes( ptyaline +
lysozyme)
 Functions 0f saliva
 Digestion : Starch + Ptyaline maltose + Maltotriose
 Lubrication of food
 Protection of buccal cavity
 Speech and cleaning
 Taste
 Antibacterial action

4. Digestion in stomach
 Secretion , composition and functions of gastric juice
 Secretion:
 cephalic phase- reflex stimulation of the vagus nerve, sight,
smell and taste of food.
 Gastric phase- gastric mucosa produced a hormone called
gastrin. The hormone stimulates the gastric gland to produce
gastric juice.
 Composition :
 Gastric juice is clear , pale yellow fluid of high acidity , 0.2-
0.5% HCl , with a pH of 1.0
 The gastric juice consist of water ,HCl, mucous, inorganic
salts, intrinsic factor and enzymes : pepsinogen , rennin and
gastric lipase

5.  Functions :
o Enzyme - pepsin
 Pepsinogen HCl Pepsin
 More pepsinogen Auto catalysis Pepsin
 Pepsin + proteins proteoses + peptones
 Pepsin + Caseinogen casein Ca Paracasenate
pepsin
Proteoses + Peptones
o Rennin : Rennin is another proteolytic enzyme. Action
of rennin is to clot milk.

6. Intestinal
digestion
Bile juice
Pancreatic
juice
Intestinal
juice/ succus
entericus
Measures against
auto digestion of
stomach
Mucous layer Tight junctions
Cell
replacement

7. Bile juice
 Cholecystokinin(CCK) is secreted from anterior part of
small intestine in the presence of meats and fats, when
it reaches gall bladder through blood it contracts the
bladder and relaxes the sphincter.
 Composition :
 water-86%, mucous(lubricant)
 mineral salts(these include Cl,CO3 and PO4 of
Na,K,Ca,NaHCO3),
 bile salts- potassium taurocholate and sodium
glycocholate (emulsifies fat)
 bile pigments- bilirubin and biliverdin(waste products)

8. Pancreatic juice
 It is secreted from hormone Cholecystokinin-
pancreozymin(CCK-PZ). It is alkaline fluid with pH of
7.5 to 8. It consists of
 water
 electrolytes – mainly from Na, K,HCo3 and Cl.
Ca,Zn,HPO4 and SO4 are present in small amounts
 Enzymes
 pancreatic amylase
 Pancreatic lipase
 Trypsin and chymotrypsin

9. Starch Maltose + Maltotriose
pancreatic amylase
Fat（Triglyceride） Monoglyceride + Fatty acids
Pancreatic Lipase
Trypsinogen Trypsin
Enterokinase
Chymotrypsinogen Chymotrypsin
protein
polypeptide
Carboxypeptidase
amino acid
Functions of pancreatic juice

10. Intestinal juice/succus entericus
 Intestinal juice secreted by lieberkuhn glands present
in the wall of small intestine gets mixed with Chyme
 Chyme stimulates the mucus membrane of small
intestine to secrete the hormone enterocrinin
 All the enzymes of intestinal juice are active in alkaline
medium pH 8.0
 Intestinal juice consists of
 Water
 Electrolytes
 enzymes

11. Small intestine Enzymes

12. Absorption
 Absorption is the passage of digested food material
through the lining of the intestine in to the blood or
lymph
 Mechanism of Absorption
 By simple diffusion
 By active transport
 Absorption of water : some water absorb through
stomach and small intestine. Most of the water
absorption is done through large intestine

13. Absorption of carbohydrates
Active transport of
carbohydrate: a
mobile carrier has
been postulated
which binds both
glucose and Na+ at
separate sites and
which transports
them both through
the plasma
membrane of the
intestinal cells.

14. Absorption of protein and fats
 Protein : Amino acids are actively transported from the
intestine the portal blood. There are several various
carrier system that exist for transporting different
classes of amino acids
 Fats :
fatty acids + monoglycerides + cholestrol micells
(3.10 nm in dia.)
Micells enter the mucosal cells by passive diffusion.

15. Absorption of vitamins
 Water soluble vitamins like B complex(except B12) and
C readily diffuse across the wall of the intestine into
the blood
 Fat soluble vitamin A,D,E and K are dissolved in
micells which enter the mucosal cells of intestine by
simple diffusion.