INTESTINAL GLANDS AND SECRETIONS

INTESTINAL GLANDS AND SECRETIONS

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 & HCO
3
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

8. MUCUS.
Brunner’s Gland –
In duodenum, thick,
alkaline & Mucoid
secretion
Protective, prevent HCl &
chyme from damaging
intestinal mucosa
Goblet cells
Secrete Mucus
Protect Mucosa &
lubricate chyme.
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

13. DIETARY CARBOHYDRATES.
Dietary intake – 250-850 g/day (50-60%)
Polysaccharides.
Starch – CH4 reserve of plants
Glycogen – Nonveg diet
Cellulose – plant.
Oligosaccharides- sucrose, lactose, maltose.
Monosaccharide – Hexose (Glucose,
Frcutose) & pentose.
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 2
nd
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

28. DIGESTION AND ABSORPTION
OF FATS
Dietary fats
Daily intake – 25-160gm
Types
Simple – TG, Cholesterol
Compound - PL
Associated – Steroids
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

41. Thursday, April 26, 2018