1. SMALL INTESTINE

2. Small intestine Important digestive and absorptive functions
Secretions and buffers provided by pancreas, liver, gall bladder
Three subdivisions:
Duodenum
Jejunum
Ileum
Ileocecal sphincter
Transition between small and large intestine

3. The Intestinal Wall

4. Histology of the small intestine
Plicae
Transverse folds of the intestinal lining
Villi
Fingerlike projections of the mucosa
Lacteals
Terminal lymphatic in villus
Intestinal glands
Lined by enteroendocrine, goblet and stem cells

5. The Structure of the Intestine

6. Intestinal Villi and Microvilli

7. GLANDS OF SMALL INTESTINE
BRUNNER’S GLANDS
Present in the duodenum
Seen in the submucosal coat
CRYPTS OF LIEBERKUHN
Present between villi
Seen in jejunum & ileum

8. BRUNNER’S GLANDS Present in duodenal mucosa In the submucosa
From pyloro-duodenal junction upto Ampulla of Vater
Small quantity – 50ml/day
Clear, viscous fluid
Specific gravity
pH 8.2 – 9.3

9. BRUNNER’S GLANDS Constituents Mucoprotein & Bicarbonate
Thick alkaline mucus
Protects duodenal mucosa from gastric juice
Little amount of Na+, K+, Cl-
Weak pepsinogen
Secretion is spontaneous
Irritation & vagal stimulation – ↑ secretion

10. GLANDS OF SMALL INTESTINE
CRYPTS OF LIEBERKUHN
Enterocytes – Digestive & absorptive
Goblet cells – mucous
Paneth cells – secrete glycoprotein, immunoglobulins & lysozymes
Enterochromaffic/Argentaffin cells serotonin – Local hormone
Intestinal motility & secretion ↑

11. SMALL INTESTINE Approximately 9 L of fluid/day Dietary sources - 2L
GIT secretions – 7 L
But only 1 – 2 L passes into the colon
SUCCUS ENTERICUS
SECRETIONS FROM
Brunner’s glands
Crypts of Lieberkuhn
Mucous from goblet cells
Shedded epithelial cells

12. SUCCUS ENTERICUS Daily secretions 3 L Colourless fluid
Sp. Gravity – 1.010
pH 7.6
Water 98.5%
Solids 1.5%

13. SUCCUS ENTERICUS Inorganic – 0.7% Cations: Na+, K+, Ca2+, Mg2+
Anions: Cl-, HCO3-, PO43-
Organic – 0.8%
Enzymes

14. Intestinal Enzymes Enterokinase (Converts Trypsinogen to Trypsin)
Disaccharide splitting enzymes: Maltase, invertase, lactase &  limiting dextrinase
Proteolytic enzymes: Erepsin, Nuclease
Intestinal Lipase
Cholesterol esterase
Lecithinase
Alkaline Phosphatase

15. Disaccharide splitting enzymes
Sucrose
Invertase
Glucose + Fructose
Maltose Maltase Glucose + Glucose
Lactose Lactase Glucose + Galactose
 limit dextrins  limiting dextrase Glucose

16. Protein splitting enzymes
Peptones & polypeptides
Erepsin
Amino acids
Nucleic acids
Nuclease
Nucleotides & nucleosides
Nucleotidase & Nucleosidase
Purine & pyrimidine

17. Fat splitting enzymes
Cholesterol esters Cholesterol esterase Free cholesterol
Lecithin & Isolecithin Phospholipase simple phospholipids
Organic phosphate Alk. Phosphatase Free phosphate

18. REGULATION Neural: Parasympathetic Sympathetic: Role not clear
Vagus – Ach - Stimulates
Sympathetic: Role not clear
Local Plexus: ↑ secretion
Mechanical – Irritation - ↑ secretion

19. Humoral regulation All GI hormones stimulates
Gastrin, CCK – PZ, Secretin, VIP, GIP, Glucagon
Somatostatin – inhibit glucagon stimulated secretion
Prostaglandin – Stimulate secretion

20. FUNCTIONS OF SUCCUS ENTERICUS
DIGESTIVE FUNCTION
PROTECTIVE FUNCTION
ACTIVATOR FUNCTION

22. L.I. as seen in Barium enema

23. MOTILITY Types of movements 1. Mixing movements
Segmentation (Haustral contractions)
2. Propulsive
Mass Peristalsis (mass movement)

24. Mixing movements
Large circular constrictions at regular intervals due to contractions of circular muscle
Longitudinal muscle (aggregated to form teniae coli) also contract
Bag-like ‘haustrations’ are formed
After few minutes, new haustral contractions occur in other nearby areas
Fecal matter is slowly dug into & rolled over
Also propel the contents slowly towards anus

25. Propulsive movements Haustral contractions slowly move contents
Mass movements rapidly move contents en masse towards rectum
Similar to peristalsis, but large areas show contraction
Last for minutes, come 1-3 times a day; usually after eating breakfast
Causes desire to ‘defecate’ if rectum is filled

26. Gastroileal reflex gastrin ↑ motility of ileum Food In
Stomach Vagovagal ↓ tone of
reflexes ileocaecal
sphincter

27. Mass movements in colon
Gastrocolic reflex
Gastric distension
Neural (ENS,ANS)
Hormonal (gastrin)
Mass movements in colon
Distension of rectum
Desire to defecate

28. GASTROCOLIC REFLEX FOOD IN STOMACH MASS PERISTALSIS DISTENSION OF
RECTUM

29. Absorption & Secretion in colon
Minimal absorption occurs in colon
Unabsorbed carbohydrates short chain fatty acids (by colonic bacteria) absorbed
Absorbs sodium by an active mechanism (influenced by Aldosterone)
Chloride is absorbed in exchange to bicarbonate, which is secreted
Absorption of water (90٪ of water delivered from SI)
Only Mucus is secreted by colon

30. Other functions
Distal colon functions principally as storage organ
Synthesis of Vitamin K, folic acid & B-complex vitamins

31. Colonic bacteria Colon contains 500 different species of bacteria
Mostly harmless & beneficial; some pathogenic
Synthesize Vitamin K, B group vitamins
Compete with pathogenic microbes for nutrition
Promote colonic motility
Maintain mucosal integrity
Produce gases by fermentation of unabsorbed carbohydrate

32. Defecation Process of emptying of rectum when distended
Is under voluntary control
Most of the time, rectum is empty of feces
Desire to defecate occurs when a mass peristalsis forces the feces into the rectum & defecation reflex begins
The act can be postponed voluntarily

33. Internal anal sphincter
Anal sphincters
Internal anal sphincter
(smooth muscle)
Rectum
Pelvic diaphragm
External anal
Sphincter (skeletal
Muscle)

34. Anal sphincters
Continuous dribble of fecal matter through the anus is prevented by tonic contraction of 2 sphincters:
Internal anal sphincter- thickening of the circular muscle; lies immediately inside anus; supplied by pelvic parasympathetic nerves
External anal sphincter- Striated voluntary muscle; surrounds the internal sphincter & extends distal to it; supplied by somatic pudendal nerve (under voluntary control)

35. Higher centers Sacral Spinal cord Pudendal nerve
Afferents
Sacral
Spinal
cord
Parasympathetic efferents
Pudendal
nerve
Distension receptors
(SOMATIC)
Both sphincters inhibited

36. Defecation reflex Receptors: distension receptors of rectum
Afferent pathway: parasympathetic nerves
Center: sacral spinal cord (S2, S3, S4)
Efferent pathway: pelvic parasympathetic, somatic pudendal
Effector structures: Descending colon, sigmoid colon, rectum (all contracted), anal sphincters (both relaxed)

37. Other factors involved in voluntary defecation
Taking deep breath to move diaphragm down
Closure of glottis
Contraction of abdominal muscles
Relaxation of pelvic floor

38. Constipation
Is a pathological decrease in colonic motility resulting in prolonged evacuation of colonic contents & delayed defecation
Frequency of defecation varies from person to person; In constipation, there is a decrease in that frequency
Results in formation of dry, hard fecal matter
Causes abdominal discomfort, dull headache, anorexia due to rectal & colonic distension
Causes: Emotions, low-bulk diet, colonic obstruction, neurological, ignoring urge to defecate

39. OUT COME
Describe composition and function of small/large intestinal secretion
Regulation of small intestinal secretion
Defecation, Constipation.