biochemistry notes for physiotherapy students.

1. DIGESTION AND ABSORPTION

2. DIGESTION OF CARBOHYDRATES
•In the diet carbohydrates are present as complex
polysaccharides (starch, glycogen), and to a
minor extent, as disaccharides (sucrose and
lactose).
• They are hydrolysed to monosaccharide units in
the gastrointestinal tract.
•Cooking makes the digestion process easier.

3. DIGESTION OF STARCH
•Begins in mouth and continues in intestine
•Salivary amylase and pancreatic amylase are the
important enzymes in starch digestion.
•Digestion in mouth
•Salivary amylase starts the digestion in mouth
•Very little digestion takes place in mouth, as the
food remain in mouth for a very short time

4. •Digestion in stomach
•Food gets mixed with gastric juice
•Digestion in intestine
•Pancreatic amylase continues digestion
of starch in intestine
•It hydrolzes alpha 1,4- glycosidic
linkage of starch and produces maltose,
isomaltose

5. •Maltase, isomaltase enzymes in
intestine, hydrolyzes disaccharide
into monosaccharides, which are
then absorbed.
•Maltose glucose
Maltase

6. ABSORPTION OF CARBOHYDRATES
•Carbohydrates are absorbed as monosaccharides
•Major monosaccharide produced by digestion of
carbohydrate is glucose, other is fructose and
galactose
•Monosaccharides are absorbed from intestinal lumen
to intestinal cells by 2 mechanisms
•1. Facilitated diffusion
•2. Active transport

7. •Glucose absorption
• Glucose is absorbed by active transport
• A carrier protein called sodium dependent glucose
transporter (SGLT-1) binds both glucose and sodium And
transport them from intestinal lumen to intestinal cells
•Fructose absorption
• Fructose and galactose are absorbed by facilitated diffusion
• A carrier protein called sodium independent transporter
(GLUT) transport fructose and galactose from intestinal
lumen to intestinal cells

8. DIGESTION OF PROTEINS
• Proteases and peptidases digests proteins
• Peptidases are of 2 types
Exopeptidases and endopeptidases
• Exopeptidases
Carboxypeptidases and aminopeptidase hydrolyse the terminal
peptide bond and release the terminal amino acid
endopeptidases
Pepsin, trypsin, chymotrypsin hydrolyses the remaining
peptide bonds

9. •Digestion in stomach
•Protein digestion takes place by HCL,
pepsin, renin in the gastric juice
•HCL
•It makes the PH optimum for action of
pepsin.
•Pepsin
•Pepsin hydrolyses peptide bonds

10. •Digestion in the small intestine
•Pancreatic juice contains enzymes like
trypsin, chymotrypsin, carboxy-pepetidase
helps in digestion
•Action of trypsin, chymotrypsin
•Hydrolyses the peptide bond

11. ABSORPTION OF AMINO ACIDS
•Free aminoacids are absorbed by 2 important
mechanisms
•1. Sodium dependent secondary active transport
system
•Sodium dependent amino acid transporter binds both
aminoacid and Na+.
•And transport them from intestinal lumen to intestinal
cells
•2. gamma glutamyl cycle

12. DIGESTION OF LIPIDS
•Major dietary lipids are triglycerides, cholesterol,
phospholipids
•Little or no digestion occur in mouth and
stomach
•Major site of lipid digestion is small intestine
Digestion of triacylglycerol
It occurs by emulsification and lipolysis

13. •Emulsification
•It is the conversion of large fat droplets
into smaller fat droplets
•Emulsification is achieved by the action
of bile salts and peristaltic contraction of
stomach

14. •Lipolysis
•Hydrolysis of triacylglycerol is carried out
by action of lipases
•In the intestine the emulsified
triacylglycerols are hydrolysed by
pancreatic lipase

15. •3 different lipases are present ; TAG
lipase, DAG Lipase, MAG lipase
•TAG; triacylglycerol
•DAG; diacylglycerol
•MAG; monoacylglycerol

17. •Digestion of phospholipids
•They are digested by pancreatic
phospholipase
•Digestion of cholesterol ester
•It is digested by cholesterol esterase
to produce cholesterol and fatty acids.

18. •Products of lipid digestion
•Free fatty acids, free cholesterol,
glycerol are the Products of lipid
digestion
•These with bile salts form mixed
micelles.

19. ABSORPTION OF LIPIDS
•The mixed micelles approaches the brush
border membrane of intestinal mucosal cells
•They are absorbed into mucosal cells by
diffusion
• 2-monoacylglycerols are reconverted to
triacylglycerol
•Cholesterol is reconverted to cholesterol esters

20. •Transport
•Triacylglycerol, cholesterol esters in the
intestinal mucosa are transported from
mucosal cells to lymph in the form of
lipoprotein known as chylomicron
•

21. ABNORMALITIES OF CARBOHYDRATE
DIGESTION

22. LACTOSE INTOLERANCE
• Deficiency of lactase enzyme leads to lactose intolerance
• Lactase hydrolyses lactose to glucose and galactose
• In Lactose intolerance lactose cannot be digested
• Types
• 1) inhertited lactase deficiency: seen in infants
• 2) Primary low lactase activity: seen in adults, decline in
lactase activity is seen.
• 3) secondary low lactase activity: due to intestinal diseases
like gastroenteritis , colitis where lactase production is
decreased.

23. •CLINICAL MANIFESTATION
•Diarrhea; since lactose is not digested it
accumulates in intestine. Lactose takes up water
and leads to diarrhea
•Lactosuria: lactose appear in urine known as
lactosuria
•Flatulence: accumulated lactose is acted upon by
intestinal bacteria to form CO2 which leads to
abdominal cramps, diarrhea, flatulence. These
together called as intolerance

24. •Diagnosis
•Giving test dose of 50g lactose and observe
prevalence of diarrhoea and rise in blood glucose
level after test dose.
•Defect in lactase will show gastric irritation and
significant rise in glucose will not be seen.

25. • Treatment
• Avoiding of milk and milk products
• Use of curd (contains enzyme lactase)

26. MALABSORPTION SYNDROME
• It is due to defective digestion or defective intestinal
absorption of nutrients
findings
1. Steatorrhea: Excessive excretion of fats, Due to
defective digestion or absorption of lipids
2. Vitamin and mineral deficiency
3. Protein deficiency

27. •Causes
• Due to acquired disorders
• Parasitic infection
• Intestinal malabsorption
• Pancreatic tumour
• Disease of gut
• Due to genetic disorders
• Inborn errors of digestion and absorption