The document discusses the digestion and absorption of proteins in the human body. It begins by outlining sources of proteins, both exogenous (dietary) and endogenous. It then details the multi-step process of protein digestion, which begins in the stomach through the action of pepsin and is completed in the small intestine by pancreatic proteases, brush border peptidases, and intracellular peptidases. Absorption involves amino acids passing through the intestinal epithelial cells via active transport, diffusion, or endocytosis. The absorbed amino acids then enter the bloodstream to be circulated throughout the body. Some abnormalities of protein digestion can occur from pancreatic diseases or lack of amino acid transporters.

1. DR NILESH KATE
MBBS,MD
PROFESSOR
ESIC MEDICAL COLLEGE, GULBARGA.
DEPT. OF PHYSIOLOGY
DIGESTION AND
ABSORPTION
OF PROTEINS

2. OBJECTIVES
 Sources of proteins
 Digestion of proteins
 Absorption of proteins
 Abnormalities of protein digestion and
absorption
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3. Sources of proteins
 Exogenous (dietary) proteins
 Endogenous proteins
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4. Exogenous (dietary) proteins
 Daily requirement -- 0.5–0.7 g/kg body
weight and for children (1–3 years), it is 4
g/kg.
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5. Exogenous (dietary) proteins
 Structure -- made of
long chains of amino
acids bound together
by peptide linkages.
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6. Exogenous (dietary) proteins
 Sources of dietary
proteins with high
biological value
 Meat, fish, eggs, cheese
and other milk
products, Soyabeans,
wheat and various
types of pulses are also
rich source of proteins.
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7. Endogenous proteins
 Total - 30–50 g/day.
 The proteins which reach
the intestine through
various gastrointestinal
secretions and those
which are present in the
desquamated epithelial
cells of the gut
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8. Digestion of proteins
 Digested by the proteolytic enzymes to
amino acids and small polypeptides.
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9. Digestion of proteins
 Digestion of proteins does not occur in the
mouth, as there are no proteolytic enzymes
in the saliva.
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10. Digestion of proteins
 Digestion of proteins, thus begins in the
stomach and is completed in the small
intestine.
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11. DIGESTION OF PROTEINS
 In stomach.
 In small intestine.
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12. Digestion of proteins in the
stomach
 Pepsin - secreted by
chief cells of the main
gastric glands in an
inactive form
(pepsinogen)
 Digest - about 10–15%
proteins entering the
GIT.
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13. Digestion of proteins in the
stomach
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Pepsinogen
Pepsin
Proteins
Proteoses,
peptones and
polypeptides
The optimum
pH for the
action
of pepsin is 2.0;

14. Digestion of proteins in the
small intestine
 Enzymes responsible
are
 Pancreatic proteases
 Brush border
peptidases
 Intracellular
peptidases
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15. Pancreatic proteases
 Digest proteins into
dipeptides, tripeptides
& small polypeptides.
 These are further
absorbed into
epithelial cells of
mucosa & digested by
intracellular enzymes
into amino acids
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16. Brush border peptidases
 Includes
aminopeptidase,
dipeptidase, tripeptidase.
 Finally converts proteins
into polypeptides &
amino acids.
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17. Intracellular peptidases
 These digest the last
dipeptides & tripeptides
into amino acids which
enters the blood.
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18. Digestion of nuclei acid and
nucleoproteins
 These are found in abundance in foods such
as liver, kidney, pancreas, yeast etc.
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19. Digestion of nuclei acid and
nucleoproteins
 Brush border enzymes as
nucleases, nucleotidase
& nucleosidase converts
nucleotides &
nucleosides into
pentoses.
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20. Absorption of proteins
 Mechanism of
absorption into
intestinal epithelial cells
occurs through luminal
membrane of epithelial
cells.
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21. Absorption of proteins
 Mechanisms
 Na dependent active
transport mechanism
 Simple diffusion
 Endocytosis.
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22. Na dependent active transport
mechanism
 Creation of
electrochemical
gradient across the
cell
 Binding of Na & amino
acids to carrier
protein
 Movement of Na &
amino acid inside cell.
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23. Simple diffusion
 The dextro amino
acids are absorbed
solely by the passive
diffusion.
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24. Endocytosis.
 Proteins absorbed by endocytosis usually excite
immunological/allergic reaction.
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25. Endocytosis.
 In newborn infants, immunoglobulins
present in the colostrum are absorbed in the
intestinal mucosa by endocytosis and impart
passive immunity to child.
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26. Further digestion in the
epithelial cells
 In the cell peptidases break the remaining
linkages of tripeptides, and dipeptides
causing release of amino acids.
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27. Transport of amino acids into
blood capillaries
 the amino acids are transported into the
interstitial space across the basolateral
membrane of the cells by facilitated or
simple diffusion.
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28. Transport of amino acids into
blood capillaries
 From the interstitium, the amino acids enter
the capillaries of villus by simple diffusion,
and then via portal vein, they reach the liver
and general circulation.
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29. Abnormalities of protein
digestion and absorption
 Inadequate absorption of proteins, due to lack of
trypsin is a common consequence of pancreatic
diseases.
 Malabsorption of amino acids due to lack of
transporters is relatively rare.
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30. OBJECTIVES seen…………..
 Sources of proteins
 Digestion of proteins
 Absorption of proteins
 Abnormalities of protein digestion and
absorption
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31. THANK YOU