3. INTRODUCTION
Duodenum – 25 cm
Jejunum and Ileum – 260 cm
Duodenum I Part
II Part
III Part
Second part of duodenum receives bile
and pancreatic secretions
4. SMALL INTESTINE
It is the major part of digestion and
absorption of carbohydrates, proteins and
fats.
It is presented with 9 litres of fluid/day (2
litres - dietary sources and 7 litres - GI
secretions).
1-2 litres passes onto the colon.
6. STRUCTURE OF SMALL INTESTINE
• Finger like projections of 1mm height – Villi
(20- 40 villi/mm2)
• Covered by columnar epithelium which has
microvilli (1 µM in length and 0.1 µM in
width).
• Each villus has a central lymphatic vessels –
lacteal.
• Villus also has nerve net & capillaries.
7. INTESTINAL GLANDS
Between villi are tubular glands - Crypts of
Lieberkuhn.
Duodenum in addition has coiled tubuloacinar
glands- Brunner’s gland.
Epithelium of crypts are mitotic, move upwards,
and shed off.
15. Epithelium – enterocyte.
Outer border of microvilli of enterocyte has
digestive enzymes.
Paneth cells in the crypts secrete defensins.
Ileum has aggregate of lymphatic nodules
Peyer’s patches.
21. MIGRATING MOTOR COMPLEX
The periodic intense electrical activity seen
in the empty stomach or small intestine that
last for 3-6 min and spread from stomach
to ileum is called MMC.
It is cyclical and repeated every 90 min.
24. TYPES OF MOVEMENTS
Rhythmic segmentation contractions (Mixing
contractions)
Pendular movements
Peristalsis
Movements of villi
25. 1.Segmentation contractions
A loop of intestine is divided into a number
of segments of nearly equal size.
As one set of contraction relaxes, a new set
begins but the contraction occur at new
points between the previous contractions.
It helps to chop the chyme 2 – 3 times per
minute.
27. Control of segmental contractions
The pacemaker for these movements - near
ampulla of Vater.
The interstitial cells of Cajal (present
between LM and CM) initiates BER which
decides the frequency of segmentation
contractions.
28. FREQUENCY
Frequency α frequency of slow waves.
Strength of contraction α frequency of spikes.
This frequency is controlled by the amplitude of
the slow waves.
+ Gastrin, CCK – PZ and motilin.
- Secretin and glucagon.
29. 12/min – duodenum and proximal jejunum.
8 - 9/min – terminal ileum.
Vagus N ↑ and sympathetic nerve ↓ the
movements.
30. FUNCTIONS OF SEGMENTATION CONTRACTIONS
Agitation of intestinal contents
It tends to increase the degree of subdivision of food
particles.
Mixing of food with intestinal secretions.
Changing the layers of food in contact with mucosa,
facilitating absorption.
31. 2. Pendular movements
These are side to side swaying movements
accompanied by lengthening and shortening of the
intestine.
Function: similar to segmentation contractions.
32.
33. 3. Peristalsis
It is defined as a wave of contraction
preceded by a wave of relaxation that
travel aborally.
38. It is neurogenic and depends on the
myenteric plexus.
They move analward at a velocity of 0.5 –
2cm / sec.
They are very weak and die out at a distance
of 3 – 5 cm.
Net movement – 1cm / min.
39. Law of the gut or polarity of intestine
Starling and Bayliss
The contractile wave is conducted only in aboral
direction.
This requires the integrity of the myenteric
plexus.
41. Factors that influence peristalsis
It is increased after a meal. This is caused by
gastro-enteric reflex.
Gastrin, CCK, insulin, and serotonin enhance GI
motility.
Secretin and glucagon inhibit small intestinal
motility.
43. PERISTALTIC RUSH
Powerful irritation of the intestinal mucosa -
relieving the SI from irritating chyme.
Initiated by physical or chemical irritation.
Powerful and rapid peristalsis.
Sweeps the contents into colon.
Cause of infective diarrhea.
44. 4. Movements of villi
They are initiated by local nervous reflexes
that occur in response to chyme.
The muscularis mucosa extends into each
villus as a filament of the smooth muscle
fiber.
47. DISORDERS OF SMALL INTESTINE
CAUSES
1. Abnormal digestion of foods –
Pancreatitis
2. Malabsorption Syndrome
Causes
Resection of small intestine
Gastro-colic fistula
Sprue
Coeliac disease
48. APPLIED PHYSIOLOGY
1. Adynamic ileus or paralytic ileus
Injury either due to surgery or due to
infection.
It reappears in the small intestine within 6
– 8 hours.
2. Mechanical obstruction of small intestine