Digestion and absorption

• Digestion is the chemical breakdown of the ingested

food into absorbable molecules.
Process: The mechanical and chemical digestive
processes have one goal: to convert food into
molecules small enough to be absorbed by the
epithelial cells of the intestinal villi.
• Absorption is a complex process, in which nutrients
from digested food, minerals and water are
harvested.
• Absorption refers to the movement of nutrients,
water and electrolytes from the lumen of the small
intestine into the cell, then into the blood.
Digestiv
e system
of man
Digestive system and associated glands
Figure : Digestion and Absorption. Digestion begins in
the mouth and continues as food travels through the
small intestine. Most absorption occurs in the small
intestine.
 CARBOHYDRATE DIGESTION
The major source of carbohydrates is found in plants
Dietary carbohydrates principally consists of .
Polysaccharides : starch, glycogen & cellulose
Disaccharides : sucrose & maltose.
Monosaccharides : Glucose & fructose
Monosaccharides need not digestion
Carbohydrates is an important diet contains
Human diet contains 60 to 80% carbohydrates
It provides main bulk to the energy to the organism.
Breakdown of carbohydrates into monosaccharides is
called as carbohydrate digestion.
 Places of carbohydrate digestion
Digestion of carbohydrates initiates in
buccal cavity, stomach and intestine
Accessory glands involved in digestion
are
1. Salivary glands
2. Pancreas
3. Gastric glands : in stomach
4. Intestinal glands : small intestine
Enzymes involved
5. Ptyalin 2. Maltase .3. lactase
4.Sucrase & 5. cellulase
 Salivary glands
• The food is masticated with the help of teeth's, broken down in to smaller pieces
• Food mix with salivary juice secreted by salivary glands (3 types)
• 1. Parotid gland (just below & infront of ears)
• 2. sublingual : present at the angle of lower jaws
• 3. Submaxillary in (located below the tongue)
• 3. Buccal glands (secret mucus)
• Saliva is highly acidic in nature (6.5 pH)
• Water contain is 99.5%, solid content is .5%
• Cellular contents of saliva are Yeast, bacteria,
• protozoa, leucocytes
• Inorganic salts (NaCl, KCI,CaCo3 Calcium phosphate, sodium phosphate)
• Enzymes includes Ptyalin (Amylase), maltase, Lipase, carbonic anhydrase
• & bacteriolytic enzyme Lysozymes
 Control of saliva secretion

• Secretion of saliva is under the control of reflex action.

• Food in the mouth
• Through sight, smell of food
• Acid salts & other chemicals also stimulate saliva secretion
 Digestion in mouth
• Starch is digested by ptyalin secreted by salivary glands.
• Salivary amylase (ptyalin) is a mixture of two enzymes
• i.e (α &β amylase)
• Starch soluble starch → erythrodextrin →achrodextrin →maltose
• Maltose Glucose
• Starch is converted in to soluble starch.
• Soluble starch is converted in to erythrodextrin.
• Erythrodextrin in turn splits in to achrodextrin.
• Archodextrin is converted in to maltose
 Starch
glycogen

Maltose Sucrose Lactose

Glucose + fructose Glucose +

Galactose Glucose

Fig : digestion of carbohydrates

 Gastric Digestion (in stomach)
• Gastric juice(transparent yellow fluid ) is the secretion of stomach.
• In man there are about 35,000000 gastric glands in stomach of man
• These are located below the surface of epithelium
• Gastric glands are formed of 4 types of cells
• 1. Mucus neck cells : secreting mucous
• 2. Chief/zymogenic/peptic cells : secreting pepsin, rennin & gelatinase.
• 3.Oxyntic or Parietal cells : secreting HCL
• 4. Argentaffin cells secrets Vasoconstrictor serotonin.
• Healthy man secrets 2000 to 3000 ml of gastric juice in 24 hrs.
• It is highly acidic in nature (Ph 0.9 to 1.5)
• Main enzymes present are pepsin, renin, lipase, pepsinogen, reninogen
 Summary of Hydrolysis of food by enzymes

Sr. Digestive juice Secretory Place of Medium and Ph substrate enzyme End product
no gland action

1. Saliva Salivary Oral Neutral or lightly Carbohydrates Salivary Maltose

glands cavity alkhalene 7-0 or starch Amylase or
ptylin

2. Gastric juice Gastric stomach Acidic 2-0 proteins Pepsin peptides

glands

Acidic 2 caseinogen Renin gastric Casein, glycerol

lipase and fatty acid
 Summary of Hydrolysis of food by enzymes
Digestive Secretory Place of Medium substrate enzyme End product
juice gland action and Ph
Pancreatic Exocrine Duodenum Alkaline 7- Proteins Trypsin, chymotrypsin, carboxy Peptides,
juice cells of 8-0 peptides peptidase amino acids
pancreas
Starch Amylase or amylopsin Maltose

Maltose Maltase Glucose

Fats Pancreatic lipase or steapsin Glycerol and

fatty acids.

RNA Ribonuclease Nucleotides.

 Summary of Hydrolysis of food by enzymes
Sr.no Digestive juice Secretory gland Place of Medium substrate enzyme End
action and Ph product
1 Pancreatic juice Exocrine cells of Duodenum Alkaline 7- Proteins Trypsin, Peptides,
pancreas 8-0 peptides chymotrypsin, amino
carboxy acids
Starch peptidase
Maltose
Maltose Amylase or
Fats amylopsin Glucose

RNA Maltase Glycerol

and fatty
Pancreatic acids.
lipase or
steapsin Nucleotid
es.
Ribonuclease
 Digestion of cellulose

• Cellulose .
• Man cannot produces cellulose.
Digestion of
protein
Options For Amino Acid Use In The Human Body
 CHEMICAL DIGESTION
Sr.no
Enzyme Category Enzyme Name Source Substrate Product
.
1. Free fatty acids, and mono- and
Salivary Enzymes Lingual lipase Lingual glands Triglycerides
diglycerides
2. Salivary Enzymes Salivary amylase Salivary glands Polysaccharides Disaccharides and trisaccharides
3. Fatty acids and
Gastric enzymes Gastric lipase Chief cells Triglycerides
monoacylglycerides
4. Gastric enzymes Pepsin* Chief cells Proteins Peptides
5. Brush border
α-Dextrinase Small intestine α-Dextrins Glucose
enzymes
6. Brush border
Enteropeptidase Small intestine Trypsinogen Trypsin
enzymes
7. Brush border
Lactase Small intestine Lactose Glucose and galactose
enzymes
8. Brush border
Maltase Small intestine Maltose Glucose
enzymes
 CHEMICAL DIGESTION
Sr.no. Enzyme Category Enzyme Name Source Substrate Product
9
Brush border α-Dextrinase Small intestine α-Dextrins Glucose
enzymes
10 Brush border
Enteropeptidase Small intestine Trypsinogen Trypsin
enzymes
11 Brush border
Lactase Small intestine Lactose Glucose and galactose
enzymes
12 Brush border
Maltase Small intestine Maltose Glucose
enzymes
13
14
Brush border α-Dextrinase Small intestine α-Dextrins Glucose
enzymes
15 Brush border
Enteropeptidase Small intestine Trypsinogen Trypsin
enzymes
16 Brush border
Lactase Small intestine Lactose Glucose and galactose
enzymes
 CHEMICAL DIGESTION
Sr.no. Enzyme Category Enzyme Name Source Substrate Product
16 Brush border
Maltase Small intestine Maltose Glucose
enzymes
17 Nucleosidases
Brush border Phosphates, nitrogenous bases,
and Small intestine Nucleotides
enzymes and pentoses
phosphatases
18 •Aminopeptidase:
amino acids at
Aminopeptidase: amino acids
Brush border the amino end of •
Peptidases Small intestine and peptides
enzymes peptides
•Dipeptidase: amino acids
•Dipeptidase:
dipeptides
19 Brush border
Sucrase Small intestine Sucrose Glucose and fructose
enzymes
20 Amino acids at
Carboxy- Pancreatic
Pancreatic enzymes the carboxyl end Amino acids and peptides
peptidase* acinar cells
of peptides
21 Brush border
Maltase Small intestine Maltose Glucose
enzymes
 CHEMICAL DIGESTION
Sr.no. Enzyme Category Enzyme Name Source Substrate Product
17 Pancreatic acinar
Pancreatic enzymes Chymotrypsin* cells Proteins Peptides

18
Pancreatic enzymes Elastase* Pancreatic acinar Proteins Peptides
cells

19 •Ribonuclease:
Pancreatic acinar ribonucleic acids
Pancreatic enzymes Nucleases cells •Deoxyribonuclease Nucleotides
: deoxyribonucleic
acids
20 Pancreatic acinar Polysaccharides α-Dextrins, disaccharides (maltose),
Pancreatic enzymes Pancreatic amylase cells (starches) trisaccharides (maltotriose)
21 Triglycerides that
Pancreatic acinar have been
Pancreatic enzymes Pancreatic lipase cells emulsified by bile Fatty acids and monoacylglycerides
salts
22 Pancreatic acinar
Pancreatic enzymes Chymotrypsin* cells Proteins Peptides

23 Pancreatic
Pancreatic enzymes Trypsin* Proteins Peptides
acinar cells
 CHEMICAL DIGESTION
Sr.n
Enzyme Category Enzyme Name Source Substrate Product
o.
23
Pancreatic enzymes Elastase* Pancreatic acinar cells Proteins Peptides

24 •Ribonuclease: ribonucleic
acids
Pancreatic enzymes Nucleases Pancreatic acinar cells Nucleotides
•Deoxyribonuclease:
deoxyribonucleic acids

25
α-Dextrins, disaccharides (maltose), trisaccharides
Pancreatic enzymes Pancreatic amylase Pancreatic acinar cells Polysaccharides (starches)
(maltotriose)

26 Pancreatic enzymes Pancreatic lipase Pancreatic acinar cells

Triglycerides that have been
Fatty acids and monoacylglycerides
emulsified by bile salts

27
Pancreatic enzymes Trypsin* Pancreatic acinar cells Proteins Peptides

28
Pancreatic enzymes Elastase* Pancreatic acinar cells Proteins Peptides

29 •Ribonuclease: ribonucleic
acids
Pancreatic enzymes Nucleases Pancreatic acinar cells Nucleotides
•Deoxyribonuclease:
deoxyribonucleic acids