1. Carbohydrates in the diet are broken down into monosaccharides like glucose, fructose, and galactose through the sequential actions of salivary amylase, pancreatic amylase, and intestinal disaccharidases. 2. These enzymes break down starches, disaccharides, and other carbohydrates into monosaccharides that can then be absorbed in the small intestine. 3. Absorbed monosaccharides enter the portal vein and are distributed throughout the body.

1. 1
Small Intestine and
Large Intestine Function & Motility

2. SMALL INTESTINE
Is part of GIT extending from pyloric sphincter of
stomach to ileocecal valve.
Major site for digestion & absorption of
carbohydrates, proteins & fats.
Length around 4-5 mts.
3 parts – Duodenum, jejunum & ileum.
Secretion from small intestine called as succus
entericus.

3. Mucous membrane of SI is covered by
Intestinal villi of height 1 mm. The villi are lined
by columnar cells called enterocytes.
Each enterocyte gives hair like projection called
microvilli, increases surface area for
absorption.
Simple tubular glands lined by columnar cells in
intestine called Crypts of Lieberkuhn.
These columnar cells show active mitosis.
Brunner’s glands seen majorly in duodenum
region.

4. Crypts of Lieberkuhn – secrete the
intestinal juice
1. Enterocytes : digestive Enzymes
2. Goblet cell : Mucus
3. Paneth cell : Glycoproteins , Immunoglobulin,
Lysozymes (defensins)
4. Enterochromaffin cells : Seretonin , 5HT
Endocrine cells: GI hormones, e.g.
Secretin, CCK, VIP, GIP

5. Volume 1800ml/day Alkaline, 8.3 pH
isotonic with plasma S.G : 1010
composed of water (about 98%)
Solids
inorganic salts
Cations - K+
, Na+
, Ca++
Anions - Cl-
,HCO3-
jejunal secretions : Cl-
, K+
is 
ileal secretions : Na+
, Ca++

SUCCUS ENTERICUS

6. Organic constituents:
Proteins
Mucin
Albumin
Immunoglobulin A
numerous shed epithelial cells of the intestinal
mucous membrane
Digestive enzymes - present in the shed
epithelial cells & little role in digestion

7. Functions of succus entericus
1) Digestive function
By Proteolytic enzymes
By Amylolytic enzymes
By Lipolytic enzymes
.
2). Protective function.
 Mucus protects lining of small intestine.
Paneth cells of intestinal glands secrete defensins
 .
3) Enterokinase present in intestinal juice
activates trypsinogen into trypsin

8. Intestinal Enzymes:
I. Activating Enzyme
Enteropeptidase or enterokinase is a brush
border enzyme of the duodenum and jejunum.
released in response to secretin, CCK or bile
acids
converts inactive trypsinogen into active trypsin.

9. II. Digestive Enzymes
(a) Proteolytic Enzymes. Break down
polypeptide into aminoacids
Carboxypeptidases
Endopeptidases
Dipeptidases
(b) Enzymes Acting on Nucleic Acids
Nuclease.
Nucleotidase
Nucleosidase

10. Fat Splitting (Lipolytic) Enzyme:
 Intestinal lipase present in the brush border of epithelial cell
 its action is much weaker than that of pancreatic
lipase.
Enzymes Acting on Carbohydrates:
 important amylolytic enzymes are the
disaccharidases
 Maltase
 Sucrase
 Lactase.
 Isomaltase
 Trehlase
 Amylase

11. Regulation of Small Intestinal
Secretion
 Local ;
 Neural ;
 Hormonal ;
Local Stimuli:
Presence of chyme in the intestine increases
intestinal secretion.
Distention of intestine stimulate secretion,
probably by local nervous reflexes.

12. 2. Extrinsic Nerves-
Vagal stimulation - increases secretion of
glands
Sympathetic stimulation inhibits secretion.
Inhibition
 helps to prevent loss of fluid & electrolyte
 help absorptive process

13. 3. Hormones:
GIT hormones: VIP, GIP & Gastrin – stimulates
intestinal secretion
Acetylcholine – increases & noradrenaline
inhibits secretion

14. 14
Small intestinal movements
Function
Mixing
Absorption
Propulsion
Types: BER MMC
Mixing - segmentation
- pendular movement
 propulsive -peristalsis

15. 15
 Types of movements
Segmentation contractions
Rhythmic contractions
Intestine is divided into segments of 1-2cms
Circular muscle contraction
Each contraction lasts for 1 – 3 second
Function
• mixing
• absorption

16. 16
Segmentation
Commonest
Alternating
contraction
Mixing

17. 17
Pendular movements
Some times seen
Simple constrictions of the intestinal wall
which moves up & down for short distances
Causes to & fro movements of chyme
Aids mixing & exposure to greater area of
mucosa
Tonic contractions
Prolonged contraction of segments of
intestine
One segment – isolated from another

18. 18
 Peristalsis
Distended bowel, causes contraction behind
the stimulus (proximal) & relaxation in front
(distal)
Velocity of peristaltic wave – 0.5 – 2.0 cms/sec
Movement of chyme – 1 cm/min
Depends on the integrity of myentric plexus.

19. 19
Acetylcholine & substance P - cause contraction
behind stimulus
VIP & Nitric oxide - cause relaxation in front of
stimulus
LAW OF GUT.

20. 20
Peristalsis
Function
Rapid propulsion
of intestinal
content
‘clearing’

21. 21
Peristaltic rush – strong / rapid peristaltic waves –
travel long distance & quickly sweep the intestinal
content into colon e.g. intestinal irritation
(catharitics) or excess distension
Antiperistalsis - vomiting

22. Peristalsis
For peristalsis,intact nerve supply has to be
there.
Do not occur in denervated intestine.
The extrinsic hormones also influence.
As parasympathetic system- stimulate &
sympathetic nerves- inhibit the peristalsis.
 Gastrin, CCK-PZ, serotonin, etc ↑, whereas
secretin,etc ↓ peristalsis.
But the presence of food in intestine is an
important stimulus.

23. 23
Movement of intestinal villi
Fasting – villi ~ inactive & lie flat
Contact with food
To & fro Lashing or swaying movements
Shorten & elongate alternately
Stirring of fluids – help in absorption, expulsion of
lymph from lacteals
Dependent on intact submucosal plexus
Stimulation
Vagal – increases movements
Sympathetic – pale & motionless

24. 24
Regulation of intestinal motility
Coordinated & regulated by –
 Local ,
 Neural &
 Hormonal mechanisms
Segmental & pendular movements – myogenic ,
occurs in denervated loop.

Peristalsis is an intrinsic neural reflex

25. 25
Extrinsic influence & regulation
Parasympathetic - Vagus – increases – tone & intestinal
motility
Sympathetic – inhibits
Humoral factors - Motility & Tone
Increased by Decreased by
Acetylcholine Noradrenalin
Serotonin Secretin
Motilin Glucagon
CCK VIP
Gastrin NO
Insulin
Histamine
Substance P

26. Applied physiology
1) Malabsorption syndrome:
Causes- a} Resection of small intestine
b} Gastro-colic fistula
c} Sprue
d} Coeliac disease
Sprue : a intestinal disorder multiple causes
leading to damaged intestinal mucosa.

27. 3) Coeliac disease: characterised by congenital
absence of enzyme gluten hydrolase in
intestinal mucosal cells, results in formation of a
toxic polypeptide ‘Gliadin’ from Gluten (protein
in barley,rye,wheat,etc).
 Gliadin causes intestinal T cells to produce an
inflammatory allergic response that flattens &
disrupts the formation of microvilli.
27

28. clinical features :
 Indigestion, diarrhoea, anorexia & weight loss,
abdominal cramps
 Nutritional defieciancy ,macrocytic anemia.
Vit B, Folic acid and Vit k defieciency.
 Osteomalcia ,
Steatorrhea .etc.
28

29. Adynamic ileus: (Paralytic ileus)
Intestines are traumatised, smooth muscles are
directly inhibited.→ motility↓
Peritoneal irritation.—reflex inhibition due to ↑
noradrenergic dischrage.
Intestines will be irregularly distended by
pockets of gas and fluid.
Treatment :obstruction relieved by aspiration of
gas and fluid by Ryle’s tube till peristalsis
returns.
29

30. 30
Large Intestine

31. 31
Functions of large intestine
Secretions
- Goblet cells secrete mucus – protective
lubricant layer. Helps in stool formation. (adherent
medium for holding fecal matter together).
Protects wall from bacterial activity.
- Secretion of bicarbonate to fight acidity
caused in stool due to bacterial action.
- Secretion of potassium.
Digestion
none except by bacteria

32. 32
Functions of large intestine (contd.)
Absorption
water & electrolytes, sodium & chlorides are absorbed.
Bile salts, certain products of bacterial action (indole) also
absorbed.
90% fluid removed , 1000-2000ml of chyme converted to
200-250ml of semisolid feaces
Excretion
Heavy metals, metabolites, drugs e.g.. Emetine.
Fluids for transfusion purposes & drugs (anesthetics)
maybe given through large gut.
Also used to transplant ureters after removal of a
pathological urinary bladder.

33. 33
Large Intestine Absorption

34. 34
Bacterial Flora
 consist of:
Bacteria surviving the small intestine that enter the cecum
and
Those entering via the anus
(pathogens,symbionts,commensals )
These bacteria:
Colonize the colon
Ferment indigestible carbohydrates
Release irritating acids and gases (flatus)
Synthesize B complex vitamins ,vitamin K,
folic acid ,short chain fatty acid

35. 35
Movements of large intestine
Colonic transit time
Food enters caecum – 4 hrs after meal
Ileum empty – 8hrs
Caecum & ascending colon empty – 13 to 17 hrs
Distal colon - 18 hrs
Rectum – 24 hrs
Some remnants of meal are present in rectum ~
72 hrs

36. 36
Types of movement
Similar to SI
Segmentation contraction – present in
proximal region of colon (i.e, ascending &
transverse region)
Haustral contractions or churning in which
colonic wall roll back & forth
Kneading movements - alternate contraction
& relaxation of large segments of colon

37. 37
Pendular type of movement – peristalsis cum
anti peristalsis causing mixing of colonic content
Peristalsis – wave of contraction sweeping down LI
Frequency less than SI

38. 38
Mass movement or mass peristalsis
 1-3 times/day
Forceful contractions
Involve contraction of large segment of colon
Propel contents into rectum & induce desire
for defecation
Mass movement can occur after meal
• Gastro colic reflex
• Duodeno colic reflex
Mediated by ANSMediated by ANS

39. 39
Defecation
A spinal reflex under voluntary control.
Rectum usually (almost) empty (retrograde
contractions return content to sigmoid, until there
is too much of it)
Just before defecation mass movement fills
rectum → ↑ pressure → reflex relaxation of inner
sphincter (smooth muscle) via parasympathetic
fibers in pelvic nerves & contraction of outer sph.
(skeletal muscle controlled intentionally via
pudendal nerves)

40. 40
Defecation
Pelvic
Nerve
Pudendal
Nerve

41. 41
Defecation
Stretch receptors in rectal wall can adapt - urge
to defecate can temporarily subside if
suppressed
Reflex controlled from sacral spinal cord,
modulated from higher levels
Voluntary signals stimulate relaxation of the
external anal sphincter and defecation occurs

42. 42
Applied aspect
Constipation: commonest disorder of large bowel motility
Cause :
Irregular bowel habits
Hypothyroidism
Anal strictures
Colon cancer
Diarrhoea: increase in frequency of passage of stools, due to
large bowel irritation
Cause:
Infection
Emotional tension (psychogenic diarrhoea)

43. 43
Adynamic or Paralytic ileus : trauma to intestine cause
inhibition of smooth muscle
Hirschsprung`s disease or aganglionic megacolon :
congenital absence of both myentric & submucous
plexus
Blind loop syndrome –excessive bacterial growth due
to stasis

44. Digestion of carbohydrates
The different carbohydrates in diet are Polysaccharides
like glycogen,amylose,amylopectin,etc
The disaccharides in the diet are sucrose, lactose,
starch,etc. , whereas monosaccharides are mostly
glucose & fructose.
Other carbohydrates in diet include Alcohol, Lactic acid,
pyruvic acid,pectins,dextrins and of course cellulose.
The end products of carbohydrates is
monosaccharides.

45. I. Carbohydrate
Starch amylase Disaccharide
(salivary, pancreatic, intestinal) (Maltose, Isomaltose, maltotriose)
+
dietary disaccharide
Sucrose + Lactose
Monosaccharide
(Glucose, fructose, galactose)
Intestinal disaccharidases.
Maltase, sucrase, lactase
Digestion

46. In the mouth: The salivary amylase present.
In the stomach: The salivary amylase act here for a
longer time. As such less enzymes (weak amylase)
present in stomach region.
In the intestine: Along with enzymes in stomach from
pancreas like pancreatic amylase & succus entericus
enzymes like maltase, sucrase, lactase,dextrinase,
trehalase,etc act on the carbohydrates in food to break it
down into m.s.
The pancreatic amylase can act both on boiled &
unboiled starch but salivary amylase acts on boiled
starch only.

47. Brokendown products (glucose) transported from lumen
of S.I. into epithelial cells in the mucus membrane of S.I
by means of sodium co-transport.
From epithelial cell, glucose is absorbed into portal vein
by facilitated diffusion.
Utilization of carbohydrates occurs mainly by oxidative
process in which the carbohydrates are burnt down
slowly to release energy. This process is called
catabolism.
The part of released energy is utilized by the tissues for
the physiological actions & rest of the energy is stored as
rich energy phosphate bonds and in the form of proteins,
carbohydrates & lipids in the tissues. This process is
called anabolism.

48. Carbohydrates: Hydrolyzed into
Monosaccharides
 Glucose is transported to cells requiring energy; insulin
influences rate of transport

49. Absorption of CHO

50. DIGESTION, ABSORPTION AND METABOLISM
OF PROTEINS.
Proteins: Food containing high protein are- meat,fish
egg & milk and the various proteins in them are collagen,
albumin,casein,lactalbumin, vitellin,etc.
Digestion of proteins: (by proteolytic enzymes)
A) Mouth- No protein digestion occurs.
B) Stomach- By pepsin & rennin
C) Small intestine- By pancreatic enzymes like
trypsin, chymotrypsin in duodenum & jejunum as
well as succus entericus which contains
dipeptidases,tripeptidases & aminopeptidases.
The final products of protein digestion are amino
acids absorbed from intestine.

51. II. Proteins & Nucleoproteins
Proteins
Proteases, peptones, large polypeptides
also digest collagen
Smaller peptides & some free a.a.
Amino acids
(98% of dietary protein)
(polypeptide chains composed
of a.a. bound by peptide linkage)STOMACH
Pepsin
DUODENUM
Pancreatic trypsin & chymotrypsin
(endopeptidase),
Carboxypeptidase (exopeptidase)
Intestinal exopeptidase (aminopeptidase,
dipeptidase, amino-tripeptidase)
Digestion

52. Absorption: in form of amino acids from small intestine.
 The levo a.a actively absorbed by sodium co-transport. Whereas
dextro a.a. by facilitated diffusion.
Area Juice Enzyme Substrate Endproduct
Mouth Saliva NO proteolytic enzyme present
Stomach Gastric juice Pepsin Proteins Proteoses,
Peptones,etc
Small
intestine
Pancreatic
juice
Trypsin Proteosus
peptones
Amino acids
Chymotrypsin
Carboxy
peptidases
A&B
Dipeptidases
Tripeptidases
Polypeptides
Succus
entericus
Dipeptidases Dipeptides
Amino acids
Tripeptidases Tripeptides

53. Nucleoproteins
Nucleotides & di-tri polynucleotide
Nucleosides
Purine & pyrimidine bases
Pancreatic nuclease
Intestinal nuclease
nucleosidase
Digestion

54. Protein & Amino Acid Transport

55. Absorption of proteins
Sources of digested proteins
50% - ingested food
25% - digested juices
25% - desquamated mucosal cells
7 different transport system transport a.a into
enterocytes
 5 – co-transport a.a & Na+
 2 – independent of Na+

56. protein absorption - jejunum & some in upper ileum
Proteins with mol wt > 200 – 300 are poorly absorbed
Intestine of newborn can absorb intact protein by
pinocytosis.
This enables absorption of antibodies from colostrum.
minute amount of native proteins is absorbed in
M – cells overlying peyer’s patches is responsible for food
allergies

57. DIGESTION OF LIPIDS
Lipids are consumed in form of neutral fats (triglycerides)
The different types of fat available are Saturated,
monounsaturated,polyunsaturated fats, etc.
The various sources are milk,cheese,butter,oils,fish,
meats,nuts,etc.
Digestion:
a) Mouth- By lingual lipase, But digestion does not occur.
b) Stomach- By Gastric lipase in gastric juice.
c) Intestine- By bile salts, pancreatic enzymes,intestinal
lipase,etc.
FINAL PRODUCTS OF FAT DIGESTION are fatty acids,
cholesterol & monoglycerides.

58. Absorption: Monoglycerides,cholesterol,etc form
miscelles and enter the enterocytes by simple diffusion.
In mucosal cells, most of monoglycerides are converted
into triglycerides. These are coated with a layer of
protein,cholesterol & phospholipids to form particles
called chylomicrons. These chylomicrons being larger
in size cannot pass through membrane of blood
capillaries.Hence these are transported through lymph
vessels and finally into blood.
Storage: The lipids are stored in adipose tissue & liver.
When the above chylomicrons are travelling through
capillaries of adipose tissue or liver, enzyme called
lipoprotein lipase present in capillary endothelium
hydrolyses triglycerides of chylomicrons into free fatty
acids (FFA) & glycerol.

59. FFA & glycerol enter fat cells of adipose tissue or liver
cells (i.e. storage points). Here again the FFA & glycerol
is converted into triglycerides and stored in these cells.
Other contents of chylomicrons such as cholesterol &
phopholipids which are released into the blood combine
with proteins to form lipoproteins.
When tissues of body need energy,the triglycerides
stored in this adipose tissue is hydrolyzed into FFA &
glycerol. The FFA are transported to the body tissues
through blood.
These lipids (FFAs) are transported in blood in
combination with albumin or in form of lipoproteins.

60. Transport of Lipids Across Intestinal
Epithelium

61. Water & Vitamin absorption
Out of 10 liters, only 100-200 ml of water is excreted out.
Osmotic difference is the driving force for water
absorption.
Plenty of water is absorbed in large intestine.
All vitamins except vitamin D which is mostly formed in
the skin are absorbed in diet. Fat soluble vitamins
absorbed along with lipids require presence of bile salts.
Vitamin B12 is majorly absorbed from ileum.
Other vitamins from jejunum..

62. Water and Ions
Water: can move in
either direction across
wall of small intestine
depending on osmotic
gradients
Ions: sodium,
potassium, calcium,
magnesium,
phosphate are
actively transported