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 ( villi/mm2)
Covered by columnar epithelium which has microvilli (1 M in length and 0.1 M 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. Outer border of microvilli of enterocyte has digestive enzymes.
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
Water %
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. Presence of food, chemical,
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 of slow waves.
Strength of contraction  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