Intestinal glands and digestion

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

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.

INTESTINAL GLANDS &
SECRETIONS
 Intestinal juice –
Succus Entericus.
 Includes aqueous
components
 Intestinal enzymes
 Mucus.
Thursday, June 18, 2020

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)

MECHANISM OF FORMATION
 Active secretion of
chloride & HCO3 ions
leads to diffusion of Na
ions followed by
osmotic movement of
water.

FUNCTIONS
 Provide solvent medium in which products of
digestion are dissolved.
 Fluid rapidly reabsorbed in villi thus provide
watery vehicle for absorption.

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)

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.

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

FUNCTIONS OF JUICE
 Mechanical functions
– Mixing & propulsive
movements.
 Digestive functions

FUNCTIONS OF JUICE
 Absorptive functions – huge surface area due to
Plicae circularis & villi & microvilli.
 Hormonal functions.
 Activator functions
 Protective function.
 Hydrolytic function.

LARGE INTESTINE
SECRETIONS
 Mainly contains Mucus by
Goblet cells & water & HCO3
ions by crypts of Liberkhun
 Mucus – lubricate faecal
matter & protect mucosa
from injury
 Alkaline Nature – netralise
acids formed from intestinal
bacteria.
 Secrete water & electrolyte
when irritated.

INTESTINAL BACTERIAL
ACTIVITY
 Bacterial Flora –
absent at birth &
develops early in life
 Intestinal bacterial
activities.
 Beneficial
 Indifferent
 Detrimental

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.

DIGESTION AND ABSORPTION
OF CARBOHYDRATE
 Dietary carbohydrates.
 Digestion of carbohydrates.
 Absorption of carbohydrate
 Fate of Glucose in body.
 Abnormalities of carbohydrate digestion and
absorption.

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.

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.

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)

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.

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.

FATE OF GLUCOSE IN BODY.
 Storage as Glycogen –
5% in liver & muscle.
 Catabolism to
produce energy – 50-
60%
 Conversion into fat –
30-40%

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

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.

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)

DIGESTION OF PROTEINS
 Pancreatic proteases –
digest protein into
Dipeptides, Tripeptides &
Polypeptides
 Brush border peptides
include dipeptidases,
tripeptidases & Nucleases
 Intracellular peptidases
final digestion to amino
acids.

DIGESTION OF NUCLEI ACID
AND NUCLEOPROTEINS
 Nuclei acid and
nucleoproteins
present in liver,
kidney, pancreas,
yeast
 In stomach
Nucleoproteins to
proteins + free
nucleic acid.

DIGESTION OF NUCLEI ACID
AND NUCLEOPROTEINS
Free nucleic acid (RNA & DNA)
Pancreatic Enzymes (Ribonucleases &
Deoxyribonuleases)
 Nucleotides & Nucleosides
Brush Border enzymes (Nuclease,
Nucleotidase, Nucleosidase)
 Pentoses (Purines & Pyrimidine)

ABSORPTION OF PROTEINS
 Into intestinal
epithelial cells
 Na dependent active
transport mechanism.

TRANSPORT OF AMINO ACIDS
IN BLOOD CAPILLARIES.
 From Epithelial cells
 Simple diffusion & Fascilitated.
 Interstitial space
Simple diffusion
 Capillaries

ABNORMALITIES OF PROTEIN
 Inadequate absorption of proteins
 Malabsorption of amino acids.

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

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.

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.

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
hydrolase
 Cholesterol & FA
 Phospholipase A2
 Hydrolyses PL &
separate FA from them.

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.

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.

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.

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.

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.

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

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.

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

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

Intestinal glands and digestion

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