Small intestine by Pandian M

FUNCTIONAL ANATOMY
INTESTINAL VILLI AND GLANDS
PROPERTIES AND COMPOSITION OF SUCCUS ENTERICUS
FUNCTIONS OF SUCCUS ENTERICUS
FUNCTIONS OF SMALL INTESTINE
REGULATION OF SECRETION OF SUCCUS ENTERICUS
METHODS OF COLLECTION OF SUCCUS ENTERICUS
APPLIED PHYSIOLOGY

1. Physiological Activities in Small Intestine Pandian M Dept. of Physiology D.Y. Patil Medical College, Kop

2. FUNCTIONAL ANATOMY SMALL INTESTINAL SECRETIONS MOTILITY OF SMALL INTESTINE FUNCTIONS OF SMALL INTESTINE APPLIED ASPECTS

3. FUNCTIONAL ANATOMY Gross anatomical considerations Structural characteristics of small intestine

4. Gross anatomical considerations The small intestine is divided into three regions. The duodenum, the shortest region, is retroperitoneal. It starts at the pyloric sphincter of the stomach Extends 25 cm (10 in.) until it merges with the jejunum. Duodenum means “12”; it is so named because it is about as long as the width of 12 fingers .

5. Contd …. The jejunum is 1 m (3 ft) long and extends to the ileum. Jejunum means “ empty ,” which is how it is found at death. The final and longest region of the small intestine, the ileum ( twisted ), measures about 2 m (6 ft) and joins the large intestine at a smooth muscle sphincter called the ileocecal sphincter.

6. Structural characteristics of small intestine Most digestion and absorption of nutrients occur in a long tube called the small intestine . Its length alone provides a large surface area for digestion and absorption , that area is further increased by circular folds, villi , and microvilli . The small intestine begins at the pyloric sphincter of the stomach, coils through the central and inferior part of the abdominal cavity,

7. Contd …. eventually opens into the large intestine. It averages 2.5 cm (1 in.) in diameter ; its length is about 3 m (10 ft) in a living person about 6.5 m (21 ft) in a cadaver due to the loss of ………??? after death .

8. Histology of the Small Intestine The wall of the small intestine is composed of the same four layers that make up most of the GI tract: mucosa , submucosa , muscularis , and serosa

9. 2. SMALL INTESTINAL SECRETIONS The intestinal juice also called succus entericus comprises the intestinal secretions which include: Aqueous component (water and electrolytes ), -especially those present in the crypts of Lieberkuhn . - 2 L of secretion is produced per day by these cells , - the chemical composition is almost similar to ECF except that it is slightly more alkaline (pH 7.5–8.6 ). -This fluid is colourless , slightly cloudy due to admixture of mucus , shedded epithelial cells and cholesterol .

10. Intestinal enzymes:- -Brush border of epithelial cells covering the villi -which secrete intracellular digestive enzymes Peptidases, Disaccharidases , Intestinal lipases, Enterokinase or ??

11. Mucus:- Brunner’s glands - thick alkaline mucoid Secretion protective role preventing HCl and chyme from damaging the duodenal mucosa . 2. Goblet cells also secrete a lot of mucus, which protects the intestinal mucosa and lubricates the chyme .

12. REGULATION OF SECRETION OF SUCCUS ENTERICUS Secretion of succus entericus is regulated by both nervous and hormonal mechanisms.

13. Stimulation of parasympathetic nerves vasodilatation ↑se SUCCUS ENTERICUS ↑se SUCCUS ENTERICUS Stimulation of sympathetic nerves vasoconstriction

14. But, role of these nerves in the regulation of intestinal secretion in physiological conditions is uncertain. the local nervous reflexes play impt role increasing the secretion of intestinal juice. Its also called local myenteric reflexes, When chyme enters the small intestine , the mucosa is stimulated by tactile stimuli or irritation . It causes the development of local nervous reflexes , (local hormone VIP is also reported to increase its secretion) . which stimulate the glands of intestine.

15. HORMONAL REGULATION When chyme enters the small intestine, intestinal mucosa secretes enterocrinin , secretin and cholecystokinin , which promote the secretion of succus entericus by stimulating the intestinal glands.

16. Secretion of Brunner’s gland is increased by: Vagus stimulation, Direct tactile stimulation or irritation of the duodenal mucosa and Secretin .

17. METHODS OF COLLECTION OF SUCCUS ENTERICUS In human beings, the intestinal juice is collected by using multilumen tube . IN ANIMALS 1.It is called Thiry loop or Thiry fistula . 2.Thiry-Vella loop is the modified Thiry loop.

18. 3. MOTILITY OF SMALL INTESTINE There are 3 types of movements:- Rhythmic segmental contractions or pendular movements and Peristalsis Tonic Contraction

19. 1.Rhythmic segmental contractions or pendular movements and Mixing movements of small intestine are responsible for proper mixing of chyme with digestive juices such as pancreatic juice , bile and intestinal juice . The mixing movements of small intestine are segmentation contractions Pendular movements .

20. occur regularly or irregularly , but in a rhythmic fashion . The ring like contractions occur at regularly spaced intervals along the gut involving localized ‘segment’ of 1-2 cm by ↑se in Ca 2+ influx . They’re two types :- Eccentric & concentric contraction also called rhythmic segmentation contractions Here the food divided & mixed with digestive juice again & again and finally formed Chyme

21. time

22. Control of rhythmic segmentation contractions ❶ Contraction is initiated by Pacemaker cells Located in 2 nd part of duodenum , near entry of bile duct A basic electric rhythm of ‘slow wave’ coordinated by myenteric reflexes

23. ❷ the frequency of contraction is directly related to the slow waves Which is initiated by Pacemaker cells I t’s not influenced by neuronal or circulatory hormones

24. ❸ the strength of contr n m is proportional to frequency of spike generated by ‘ slow waves ’ This frequency is controlled by amplitude of ‘ slow wave ’ amplitude of ‘slow wave’ ↑ sed by GIT hormones released during digestion e.g. gastrin , CCK-PZ & motilin Whereas, secretin and glucagon ↓se slow wave amplitude

25. Note – vagus N ↑& sympathetic N ↓ ❹5HT released during contr n make the smooth muscle sensitive to distension Distension of short segment causes – proximal seg . contr n & distal seg . relaxation

26. Pendular Movement

27. 2.Peristalsis Stretched or distended by food ( chyme ) Which push the chyme in aboral direction through intestine . The movement also called as vermicular or peristaltic movements. It moves analwards at rate of 0.5 to 2cm/min But its weak & dies out after travelling only 3 to 5 cm, rarely up to 10cm So net movement of chyme in analward direction is (1cm/min) slow

28. Starling’s law of intestine or law of gut or Polarity of the intestine:- The peristaltic waves always travel from the oral end towards the aboral end of the intestine. This phenomenon has been labelled as the Law of the intestine

29. Factor influence peristalsis It is increased after meal. This is caused by gastro- enteric reflex (N.C) Gastrin , CCK, insulin, and serotonin enhance GI motility (H.C) Secretin and Glucagon inhibit or reduce the intestinal motility

30. Functions subserved by the peristaltic waves are : Help to propel the intestinal contents aborally . Also help in digestion and absorption of the food particles because different types of nutrients are digested and absorbed in different segments of the small intestine

31. Peristaltic rush Initiated by chemical or physical irritation the small intestine shows a powerful peristaltic contraction . Initiated by extrinsic nervous reflex & partly by myenteric relex . It is caused by excessive irritation of intestinal mucosa or extreme distention of the intestine. This type of powerful contraction begins in duodenum and passes through entire length of small intestine reaches the ileocecal valve within few minutes. This is called peristaltic rush or rush waves . Peristaltic rush sweeps the contents of intestine into the colon .

32. Functions of ileocaecal Ileocaecal valve prevent back flow of feacal content from colon into small intestine The valve usually resists pressure of 50 to 60cm of H 2 O Gastrin produces relaxt n & Secretin causes contr n These agent show opposite effects on cardiac sphincter

33. Tonic contraction These’re relatively prolonged contract n that isolate one segment of intestine from another Along with segmental contr n , permits longer contact of chyme with enterocytes and promotes absorpt n

34. Applied 1. Adynamic ileus or Paralytic ileus :- It’s painless condition produced by (a)Handling - - of intestine during abdominal operations or trauma to intestine This causes direct inhibition of smooth muscle (b) Irritation- - of peritoneum causes reflex inhibition of smooth muscle due to ↑ non adrenergic fibers in splanchnic nerves & (b) ↓ intestinal motility to cause adynamic ileus .

35. 2. Mechanical obstruction This condition associated with production of sever pain ?? This pressure in the segment causing : ( i ) compression of blood vessels – local ischemia (ii) stimulate visceral afferent nerve fibers to cause sweating, Ht, & severe vomiting . if not relieved it may prove fatal due to resultant metabolic alkalosis & dehydration.

36. Gastro – Ileal reflex When food leaves the stomach, the caecum reflex Passage of chyme through the ileocaecal valve ↑ - so called. This is vagally mediated reflex Sympathetic stimul n ↑ contr n of the valve

37. Referred :- Text book of Medical Physiology Guyton, 13 th edition, Text book of Medical Physiology Indu khurana , Text book of Medical Physiology Vander’s Text book of Medical Physiology Sembulingam & LPR

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