1. DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
ESIC MEDICAL COLLEGE, GULBARGA.
DEPT. OF PHYSIOLOGY
INTESTINAL
GLANDS AND
DIGESTION AND
ABSORPTION.
2. OBJECTIVES.
Intestinal glands & secretions
Functions
Digestion and absorption of carbohydrate
Digestion and absorption of proteins
Digestion and absorption of fats
Absorption of water.
Applied aspects.
3. INTESTINAL GLANDS &
SECRETIONS
Intestinal juice –
Succus Entericus.
Includes aqueous
components
Intestinal enzymes
Mucus.
Thursday, April 26, 2018
4. AQUEOUS COMPONENTS
Mainly water & electrolyte
secreted by epithelial cells
of intestines(Crypts of
Liberkuhn)
2L/Day
Same as ECF but slightly
alkaline,
Colorless, cloudy (Mucus,
Epitelial cells & cholesterol)
Thursday, April 26, 2018
5. MECHANISM OF FORMATION
Active secretion of
chloride & HCO3 ions
leads to diffusion of Na
ions followed by
osmotic movement of
water.
Thursday, April 26, 2018
6. FUNCTIONS
Provide solvent medium in which products of
digestion are dissolved.
Fluid rapidly reabsorbed in villi thus provide
watery vehicle for absorption.
Thursday, April 26, 2018
7. INTESTINAL ENZYMES
This causes final hydrolysis of
food before absorption.
Mode of secretion of this
enzyme- Holocrine
Enzymes are –
Peptidases (Peptide – AA),
Diasaccharidases (Di – Mono)
Intestinal Lipase (split TG),
Enterokinase (Trypsinogen –
Trypsin)
Thursday, April 26, 2018
9. REGULATION OF SECRETIONS
Local stimuli
Mechanical (Distension), Chemical irritation.
Role of VIP – Increases secretions
Secretions of Brunner’s gland increased by
Vagus stimulation, Direct stimulation, & Secretin
Thursday, April 26, 2018
10. FUNCTIONS OF JUICE
Mechanical functions
– Mixing & propulsive
movements.
Digestive functions
Thursday, April 26, 2018
11. FUNCTIONS OF JUICE
Absorptive functions –
huge surface area due
to Plicae circularis &
villi & microvilli.
Hormonal functions.
Activator functions
Protective function.
Hydrolytic function.
Thursday, April 26, 2018
12. DIGESTION AND ABSORPTION
OF CARBOHYDRATE
Dietary carbohydrates.
Digestion of carbohydrates.
Absorption of carbohydrate
Fate of Glucose in body.
Abnormalities of carbohydrate digestion and
absorption.
Thursday, April 26, 2018
14. DIGESTION OF
CARBOHYDRATES.
In mouth – mainly
starch Digestion to
maltose by α-amylase
in saliva.
In stomach – α-amylase
continues for 30 min till
HCl comes, optimum pH
for action is 6-7 but
activity stops in
stomach when pH <4.
Thursday, April 26, 2018
15. DIGESTION OF
CARBOHYDRATES.
In small intestine
Pancreatic α-amylase –
released in 2nd
part of
duodenum in alkaline
medium
Polysachhride (starch,
glycogen)
Pancreatic amylase.
Oligosachhrides
(Maltose, Dextrin)
Thursday, April 26, 2018
16. DIGESTION OF
CARBOHYDRATES.
Brush border enzymes
of small intestine
Dextrinase, maltase,
sucrase, lactase.
Dextrin to glucose
Maltose to glucose
Sucrose to Glucose+
Fructose
Lactose to Glucose+
Galactose.
Thursday, April 26, 2018
17. ABSORPTION OF
CARBOHYDRATE
Site of absorption from the
mucosal surface of jejunum
& upper ileum.
Mechanism of absorption
Glucose & Galactose By Na
dependent active transport
system
Fructose – Fascilitated
diffusion.
Pentose – Simple diffusion.
Thursday, April 26, 2018
18. FATE OF GLUCOSE IN BODY.
Storage as Glycogen –
5% in liver & muscle.
Catabolism to
produce energy – 50-
60%
Conversion into fat –
30-40%
Thursday, April 26, 2018
19. ABNORMALITIES OF CARBOHYDRATE
DIGESTION AND ABSORPTION.
Lactose intolerance –
Congenital – due to
deficiency of enzyme
Lactase.
Leads to Diahhroea &
electrolyte Imbalance.
Secondary lactase
deficiency
Causes intestinal
distension, flatulence,
diahhroea
Thursday, April 26, 2018
20. DIGESTION AND ABSORPTION
OF PROTEINS
Sources
Exogenous – Daily
requirement 0.5-0.7 g/kg
Sources – meat, fish,
eggs, milk, soyabean.
Endogenous (30-50
gm/day)
From various GIT
secretions
Present in desquamated
epithelial cells of Gut.
Thursday, April 26, 2018
21. DIGESTION OF PROTEINS
In stomach
Pepsin – by chief cells of
main gastric glands
Digest 10-15%
Pepsinogen to pepsin by
HCL
Pepsin splits proteins to
Proteoses, peptones &
polypeptides.
Optimum pH – 2 (acid
need for digestion)
Thursday, April 26, 2018
22. DIGESTION OF PROTEINS
In small intestine
Pancreatic proteases –
digest protein into
Dipeptides, Tripeptides &
Polypeptides
Brush border peptides
include dipeptidases,
tripeptidases & Nucleases
Intracellular peptidases
final digestion to amino
acids.
Thursday, April 26, 2018
23. DIGESTION OF NUCLEI ACID
AND NUCLEOPROTEINS
Nuclei acid and
nucleoproteins
present in liver,
kidney, pancreas,
yeast
In stomach
Nucleoproteins to
proteins + free
nucleic acid.
Thursday, April 26, 2018
24. DIGESTION OF NUCLEI ACID
AND NUCLEOPROTEINS
In small intestine
Free nucleic acid (RNA & DNA)
Pancreatic Enzymes (Ribonucleases &
Deoxyribonuleases)
Nucleotides & Nucleosides
Brush Border enzymes (Nuclease,
Nucleotidase, Nucleosidase)
Pentoses (Purines & Pyrimidine)
Thursday, April 26, 2018
25. ABSORPTION OF PROTEINS
Into intestinal
epithelial cells
Na dependent active
transport mechanism.
Thursday, April 26, 2018
26. TRANSPORT OF AMINO ACIDS
IN BLOOD CAPILLARIES.
From Epithelial cells
Simple diffusion & Fascilitated.
Interstitial space
Simple diffusion
Capillaries
Thursday, April 26, 2018
27. ABNORMALITIES OF PROTEIN
DIGESTION AND ABSORPTION
Inadequate absorption of proteins
Malabsorption of amino acids.
Thursday, April 26, 2018
29. DIGESTION OF FATS
Site – Mainly in small
intestine.
Mechanism of digestion.
Emulsification of fats by bile
salts
Hydrolysis of fat droplets by
pancreatic and intestinal
Lipolytic enzymes.
Acceleration of fat digestion
by Micelle formation.
Thursday, April 26, 2018
30. EMULSIFICATION OF FATS BY
BILE SALTS
Emulsification –
Breaking of large drops
into small droplets is
must for Pancrease
lipase to act.
It is done by bile salts
Lecithin greatly
enhances this action.
Thursday, April 26, 2018
31. HYDROLYSIS OF FAT DROPLETS BY
PANCREATIC AND INTESTINAL LIPOLYTIC
ENZYMES.
Pancreatic lipolytic
enzyme -3 types
Pancreatic lipase – it
hydrolyses almost all
TG to 2 FA & 2
monoglycerides.
Cholesterol ester
hydrolase
Cholesterol ester
Cholesterol ester
hydrolase
Cholesterol & FA
Phospholipase A2
Hydrolyses PL &
separate FA from them.
Thursday, April 26, 2018
32. ACCELERATION OF FAT DIGESTION
BY MICELLE FORMATION.
MICELLE - small water
soluble cylindrical disc
shaped particles.
Composed of central fat
globule surrounded by
30 molecules of bile salts.
Monoglycerides & FFA
are incorporated in
central fatty portion.
Thursday, April 26, 2018
33. ABSORPTION OF FATS
Mostly in Duodenum.
Steps
Transportation as a
micelles to the brush
border membrane
Diffusion of lipids across
the Enterocyte cell
membrane.
Transport of lipids from
inside the enterocytes to
the interstitial space.
Thursday, April 26, 2018
34. TRANSPORT OF LIPIDS FROM INSIDE THE
ENTEROCYTES TO THE INTERSTITIAL
SPACE.
Mechanism
Diffusion across the
basal border of
enterocytes.
Formation and excretion
of chylomicrons from the
enterocytes by
exocytosis.
Thursday, April 26, 2018
35. TRANSPORT OF LIPIDS INTO
CIRCULATION
After exit from
enterocytes
chylomicrons merge
into larger droplets.
From interstitium then
diffuse into lacteals
then to lymphatic
circulation & then via
thoracic duct to enter
circulation.
Thursday, April 26, 2018
36. ABSORPTION OF WATER
Water balance in GIT
GIT receives about 9 L water/day
2L – Ingested
7L – From salivary, gastric, biliary, Pancreatic & Intestinal
secretions.
Total absorption 8.8L/day
60% - In Jejunum
20-25% - Ileum
10-15% - colon.
Thursday, April 26, 2018
37. MECHANISM OF WATER
ABSORPTION.
Passively & Iso
Osmotically following
osmotic gradient due to
absorption of electrolyte
& nutrients
In Duodenum – Due to
chyme
In Jejunum & Ileum –
reabsorption of NaCl
Thursday, April 26, 2018
38. MECHANISM OF WATER
ABSORPTION.
In small intestine –
Na-Glucose cotransport,
Na-amino acid
cotransport,
Na-H counter transport
In colon – passive
diffusion via Na
channels & stimulated
by aldosterone.
Thursday, April 26, 2018
39. APPLIED ASPECTS.
Malabsorption
syndrome – Multiple
nutritional deficiency
states are produced.
Features –
General weakness, anaemia
& signs of Hypovitaminosis
Iron deficiency anaemia
Steatorrhoea
Dehydration.
Thursday, April 26, 2018
40. CONDITIONS CAUSING
MALABSORPTION SYNDROME….
Coeliac disease (Gluten Hydrolase)
Sprue (Vit B12 & Folate)
Crohn’s disease (IBD)
Resection of small intestine.
Gastro-colic fistula
Blind loop syndrome – formation of areas of intestine where
bacteria can proliferate without being subjected to
movement down th intestine
Thursday, April 26, 2018