The small intestine is responsible for the digestion and absorption of nutrients. It is made up of the duodenum, jejunum, and ileum. The small intestine contains finger-like villi covered in microvilli that increase surface area for absorption. Glands including crypts of Lieberkuhn and Brunner's glands secrete enzymes and mucus. Movement patterns in the small intestine include segmentation contractions that mix contents, peristalsis that propels contents aborally, and villi movements that enhance absorption. Disorders can impair digestion or absorption.

1. SMALL INTESTINE

2. ORGANISATION OF GUT WALL

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.

5. MUCOSA OF SMALL INTESTINE

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.

8. STRUCTURE OF VILLI

9. VILLI

10. ENTEROCYTE

11. STRUCTURE OF VILLI

12. STRUCTURE OF VILLI

13. CRYPTS OF LIEBERKUHN

14. CRYPTS OF LIEBERKUHN

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.

17. INTESTINAL JUICE- SUCCUS ENTERICUS
COMPOSITION
Daily secretion – 3 litres
pH - 7.6
Water - 98.5%
Solids - 1.5%
i) Inorganic - 0.7%
Cations - Na+, K+, Ca2+, Mg2+
Anions - Cl-, HCO3-,PO43-

18. INTESTINAL ENZYMES
 Enterokinase
 Proteolytic enzymes
1) Erepsin
2) Nucleases
 Sucrase, Maltase, Lactase, α- dextrinase
 Intestinal Lipase
 Cholesterol esterase
 Lecithinase
 Alkaline Phosphatase

19. CONTROL OF SECRETION
 Presence of food, chemical,
mechanical stimuli - ↑ secretion
 Local irritation - ↑ mucus secretion.
 Vagal stimulation - ↑ secretion of
Brunner’s gland.

20. MOVEMENTS OF SMALL INTESTINE

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.

22. SMALL INTESTINE
Inner circular (thicker)
Outer longitudinal (thinner)

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.

26. SEGMENTATION CONTRACTIONS

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.

33. 3. Peristalsis
It is defined as a wave of contraction
preceded by a wave of relaxation that
travel aborally.

34. PERISTALSIS

35. PERISTALSIS

37. Peristalsis

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.

40. MECHANISM OF PERISTALSIS

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.

42. Functions of peristalsis
Progression of the chyme towards the ileo-
caecal valve.
Spreading of the chyme along the intestine .

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.

45. Lashing movements
Villus pump
Function: These movements accelerate the
flow of blood and lymph and increase the
absorption.

46. Villi movements

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

49. Thank you