Intestinal glands and digestion

INTESTINAL GLANDS AND DIGESTION

1. DR NILESH KATE
MBBS,MD
PROFESSOR
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 –
SuccusEntericus.
Includes aqueous
components
Intestinal enzymes
Mucus.
Thursday, June 18, 2020

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,
Epitelialcells & cholesterol)
Thursday, June 18, 2020

5. MECHANISM OF FORMATION
Active secretion of
chloride & HCO
3ions
leads to diffusion of Na
ions followed by
osmotic movement of
water.
Thursday, June 18, 2020

6. FUNCTIONS
Provide solventmediumin which products of
digestion are dissolved.
Fluid rapidly reabsorbed in villithus provide
watery vehiclefor absorption.
Thursday, June 18, 2020

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, June 18, 2020

8. MUCUS.
Brunner’s Gland –
In duodenum, thick,
alkaline & Mucoid
secretion
Protective, prevent HCl&
chymefrom damaging
intestinal mucosa
Goblet cells
Secrete Mucus
Protect Mucosa &
lubricate chyme.
Thursday, June 18, 2020

9. REGULATION OF SECRETIONS
Local stimuli
Mechanical (Distension), Chemical irritation.
Role of VIP–Increases secretions
Secretions of Brunner’s glandincreased by
Vagus stimulation, Direct stimulation, & Secretin
Thursday, June 18, 2020

10. FUNCTIONS OF JUICE
Mechanical functions
–Mixing & propulsive
movements.
Digestive functions
Thursday, June 18, 2020

11. FUNCTIONS OF JUICE
Absorptive functions –huge surface area due to
Plicaecircularis& villi& microvilli.
Hormonal functions.
Activator functions
Protective function.
Hydrolytic function.
Thursday, June 18, 2020

12. LARGE INTESTINE
SECRETIONS
Mainly contains Mucus by
Goblet cells & water & HCO3
ions by crypts of Liberkhun
Mucus–lubricate faecal
matter & protect mucosa
from injury
AlkalineNature–netralise
acids formed from intestinal
bacteria.
Secrete water & electrolyte
when irritated.
Thursday, June 18, 2020

13. INTESTINAL BACTERIAL
ACTIVITY
Bacterial Flora–
absent at birth &
develops early in life
Intestinal bacterial
activities.
Beneficial
Indifferent
Detrimental
Thursday, June 18, 2020

14. INTESTINAL BACTERIAL
ACTIVITY
Beneficial –
Synthesis of vitamin C, B complex & folic acid
Trophic effects
Indifferent
Production of intestinal gases –H2S, CO2, H2, CH4 & N2
organic acid formation
Formation of indole, skatole, mercaptans & Pigments.
Detrimental –
Consumptions of nutrients by bacteria
Production of ammonia.
Thursday, June 18, 2020

15. 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, June 18, 2020

16. DIETARY CARBOHYDRATES.
Dietary intake–250-850 g/day (50-60%)
Polysaccharides.
Starch–CH4 reserve of plants
Glycogen–Nonvegdiet
Cellulose–plant.
Oligosaccharides-sucrose, lactose, maltose.
Monosaccharide–Hexose(Glucose,
Frcutose) & pentose.
Thursday, June 18, 2020

17. DIGESTION OF
CARBOHYDRATES.
In mouth–mainly
starch Digestion to
maltose byα-amylase
in saliva.
In stomach–α-amylase
continues for 30 min till
HClcomes, optimum pH
for action is 6-7 but
activity stops in
stomach when pH <4.
Thursday, June 18, 2020

18. 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, June 18, 2020

19. 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, June 18, 2020

20. ABSORPTION OF
CARBOHYDRATE
Site of absorption from the
mucosal surface of jejunum
& upper ileum.
Mechanism of absorption
Glucose & GalactoseBy Na
dependent active transport
system
Fructose–Fascilitated
diffusion.
Pentose–Simple diffusion.
Thursday, June 18, 2020

21. FATE OF GLUCOSE IN BODY.
Storage as Glycogen–
5% in liver & muscle.
Catabolismto
produce energy –50-
60%
Conversion into fat–
30-40%
Thursday, June 18, 2020

22. 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, June 18, 2020

23. 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, June 18, 2020

24. DIGESTION OF PROTEINS
In stomach
Pepsin–by chief cells of
main gastric glands
Digest10-15%
Pepsinogento pepsin by
HCL
Pepsin splits proteins to
Proteoses, peptones &
polypeptides.
Optimum pH –2 (acid
need for digestion)
Thursday, June 18, 2020

25. 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, June 18, 2020

26. 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, June 18, 2020

27. 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, June 18, 2020

28. ABSORPTION OF PROTEINS
Into intestinal
epithelial cells
Na dependent active
transport mechanism.
Thursday, June 18, 2020

29. TRANSPORT OF AMINO ACIDS
IN BLOOD CAPILLARIES.
From Epithelial cells
Simple diffusion & Fascilitated.
Interstitial space
Simple diffusion
Capillaries
Thursday, June 18, 2020

30. ABNORMALITIES OF PROTEIN
DIGESTION AND ABSORPTION
Inadequate absorption of proteins
Malabsorption of amino acids.
Thursday, June 18, 2020

31. DIGESTION AND ABSORPTION
OF FATS
Dietary fats
Daily intake –25-160gm
Types
Simple–TG, Cholesterol
Compound-PL
Associated–Steroids
Thursday, June 18, 2020

32. DIGESTION OF FATS
Site–Mainly in small
intestine.
Mechanism of digestion.
Emulsificationof fats by bile
salts
Hydrolysisof fat droplets by
pancreatic and intestinal
Lipolyticenzymes.
Acceleration of fat digestion
by Micelleformation.
Thursday, June 18, 2020

33. 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
Lecithingreatly
enhances this action.
Thursday, June 18, 2020

34. 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
PhospholipaseA2
Hydrolyses PL &
separate FA from them.
Thursday, June 18, 2020

35. 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, June 18, 2020

36. ABSORPTION OF FATS
Mostly in Duodenum.
Steps
Transportation as a
micelles to the brush
border membrane
Diffusion of lipids across
the Enterocytecell
membrane.
Transport of lipids from
inside the enterocytes to
the interstitial space.
Thursday, June 18, 2020

37. 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, June 18, 2020

38. 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, June 18, 2020

39. 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, June 18, 2020

40. MECHANISM OF WATER
ABSORPTION.
Passively & Iso
Osmoticallyfollowing
osmotic gradient due to
absorption of electrolyte
& nutrients
In Duodenum–Due to
chyme
In Jejunum & Ileum–
reabsorption of NaCl
Thursday, June 18, 2020

41. 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, June 18, 2020

42. APPLIED ASPECTS.
Malabsorption
syndrome–Multiple
nutritional deficiency
states are produced.
Features–
General weakness, anaemia
& signs of Hypovitaminosis
Iron deficiency anaemia
Steatorrhoea
Dehydration.
Thursday, June 18, 2020

43. 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 thintestine
Thursday, June 18, 2020

44. Thursday, June 18, 2020