Digestion, Digestive juices, Absorption, Local hormones of GIT

1. Chemistry of digestionChemistry of digestion
& absorption, Local& absorption, Local
hormones of GIThormones of GIT
Dr Ifat Ara Begum
Associate Professor
Dept of Biochemistry
Dhaka Medical College, Dhaka
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2. 2

3. What is Digestion?What is Digestion?
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 It is the process by which complex food
materials are broken down into simple
absorbable units
 Based on how food is broken down:
I.Mechanical digestion
II.Chemical digestion

5. What is the basic process of digestion?What is the basic process of digestion?
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 Basic process:
Hydrolysis
 Enzymes involved:
Hydrolases group of enzymes found in
digestive juices

7. Functions of digestive systemFunctions of digestive system
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 Ingestion
 Secretion of water, acid, buffer and
enzyme in to gastrointestinal lumen
 Mixing and propulsion
 Digestion
 Absorption
 Excretion (Defecation)

8.
8
Digestive
juices

9. 9
Name Source Secretion
(L/day)
pH Imp.
component
Saliva Salivary
glands
0.75-1.5 6.7-7.0 Mucus,
Salivary
amylase,
[Lingual
lipase]
Gastric
juice
Gastric
glands
2- 2.5 1.5-2.0 Mucus,
HCl,
Pepsin,
Intrinsic
factor of
castle,
[Gastric
lipase]

10. 10
Name Source Secretio
n
(L/day)
pH Imp. component
Pancreati
c juice
Pancrea
s
0.8
-1.2
8.0
-
8.3
1)Amylolytic
enzyme:
• P. amylase
2)Lipolytic
enzyme:
• P. lipase
• Cholesterol -
esterase
•Phospholipase A2
3)Proteolytic
enzyme
•Trypsin
•Chymotrypsin
•Carboxypeptidase

11. 11
Name Source Secretion
(L/day)
pH Imp.
component
Bile Liver 0.5-1.0 7.8 •Bile salts
•Bile
pigments
(e.g.
bilirubin)
• Cholesterol
ester
• PL (lecithin)

12. 12
Name Source Secretion
(L/day)
pH Imp. component
Succus
entericu
s
Small
intestin
al
mucosa
1.0-2.0 7.5 1) Amylolytic
enzyme:
• Maltase
•Sucrase
•Lactase
•α-limit
dextrinase 2)
Proteolytic
enzyme:
•Aminopeptidas
e
•Di & tri
peptidases
3) Enterokinase/
Enteropeptidase

13. 13

14. 14

15. 15

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17. What is Absorption?What is Absorption?
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 It is the process by which end product
of digestion, water, electrolytes,
minerals & vitamins pass through the
intestinal epithelium to enter into
blood / lymph
Glucose, AA -> Blood
Fatty acid -> Lymph

18. 18

19. Processes involved in absorptionProcesses involved in absorption
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 Active transport
 Diffusion

20.
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Local
Hormones of
GIT

21. What is this?What is this?
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 A group of hormones liberated from the GIT
mucosa in response to the presence of food
in the lumen of the gut.

22.
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Name Origin Stimulus
for
secretion
Function
Gastrin G cell of
stomach
Products
of protein
digestion
Stimulates secretion
of :
Gastric acid
Pepsin
CCK Duodenu
m &
jejunum
Products
of :
Protein
digestion
Fat & FA
Stimulate enzyme
rich pancreatic
secretion
Contraction of GB
Decrease gastric
acid secretionSecreti
n
Duodenu
m &
jejunum
Acid
chyme
FA
Stimulate HCO3
rich pancreatic
secretion
Stimulate bile
secretion
Decrease gastric

24. 24
Name Origin Stimulus
for
secretion
Function
Somatostati
n
D cells of
GIT
Fat
ingestion
Inhibit gastrin &
gastric acid
secretion
Inhibit
pancreatic
secretion
GIP Duodenu
m &
jejunum
Nutrients Inhibit gastric
acid secretion
VIP Nerve
ending of
GIT
- Decrease
gastric
secretion
 Increase
pancreatic

25.
25
Digestion
&
Absorption of
Carbohydrate

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28. End product of carbohydrateEnd product of carbohydrate
digestiondigestion
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 Glucose
 Fructose
 Galactose
If starch : Only glucose

29. Absorption by Na+ dependant secondary activeAbsorption by Na+ dependant secondary active
transport (SGLT) & Facilitated diffusiontransport (SGLT) & Facilitated diffusion
(GLUT)(GLUT)
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30.
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31.
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Digestion
&
Absorption of
Protein

32. Proteolytic enzymes: TypesProteolytic enzymes: Types
32

33.
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34.
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35.
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36. End product of protein digestionEnd product of protein digestion
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 A mixture of free AA, di and
tripeptides, all of which are absorbed
actively from lumen to cell

37.
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38.
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39.
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Digestion
&
Absorption of
Lipid

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43. End product of lipid digestionEnd product of lipid digestion
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 FA
 Glycerol
 2-MAG
 Cholesterol
 LysoPL
All these are of amphipathic nature
having hydrophilic and hydrophobic
group

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46.
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Summary on
digestion &
absorption of
nutrients

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