Small intestine and large intestine

1. Small intestine and Large
intestine
Dr. Sai Sailesh Kumar Goothy
Associate Professor
Department of Physiology
RDGMC, Ujjain

2. Small intestine
Extends from pyloric sphincter to the ileo cecal valve
Length of small intestine about 300 cm during life and
700 cm after death
 This is because the smooth muscle of small intestine
is in a state of tonic contraction during life and this
tone is lost after death.

3. Parts of Small intestine
Duodenum is the first part of small intestine
C shaped
 30 cm in length
Referred as hypophysis of abdomen
Secretes number of hormones

4. Parts of Small intestine
Jejunum is second part
Constitutes about 40 % of small intestine

5. Parts of Small intestine
Ileum forms rest 60%
Ends in the colon
At the ileocecal valve

6. Parts of Small intestine
Mucosa of small intestine is thrown into a number of
valve like folds called valvulae conniventes
Contain finger like projections called villi
Free edges contain microvilli
Microvilli makeup the brush border of small intestine
Tight junctions connect the adjacent epithelial cells

7. Parts of Small intestine
20-40 villi per square millimeter of mucosa
Each villus is about 0.5-1mm long lined by single
layer of columnar epithelial cells called
enterocytes.

8. Glands of Small intestine
Crypts of lieberkuhn
Simple tubular glands
Lined by columnar epithelial cells
Contain digestive enzymes, paneth cells, goblet cells
and argentaffin cells
Argentaffin cells secrete serotonin

9. Brunner’s glands
Small, coiled, acinotubular glands
Present in duodenum
Secrete alkaline mucus
Protect duodenal mucosa from the acid chyme
coming from stomach

10. Small intestine juice
Succus entericus
Rate of secretion 1-2 lit/day
pH- 6.5-9
Water 99%
Solids 1%

11. Small intestine juice
Inorganic constituents – Sodium, Potassium,
Chloride,Phosphate etc
Organic constituents –shed enterocytes containing
digestive enzymes, albumin, globulin, mucus etc.

12. Enzymes
 Protein spilitting enzymes are enterokinases, amino
peptidases, carboxy peptidases, tetra peptidases, di
peptidases etc.
 They convert peptones and poly peptides to amino acids
 Nucleasesare nucleotidases and nucleosidases that convert
nucleic acids into purine and pyramidine bases

13. Enzymes
Carbohydrate spitting enzymes
Maltases – converts maltose to glucose
Lactases – converts lactose to galactose and glucose
Sucrase – Converts sucrose into glucose and fructose
Alfa dextrinase – converts dextrin to glucose
Trehalase – converts trehalose to glucose

14. Enzymes
Lipases
Converts triglycerides to fatty acids

15. Functions of small intestine
Mechanical function
Mixing or segmentation contractions in small intestine
Help in mixing chyme coming from stomach into the
intestine with pancreatic juice, bile and intestinal juice
for proper digestion

16. Functions of small intestine
Digestive function
End stages of digestion occurs in small intestine

17. Functions of small intestine
Absorptive function
Final products of digestion, vitamins, minerals,
water etc are absorbed in the small intestine
The villi and microvilli are responsible for
absorption

18. Functions of small intestine
Endocrine function
APUD cells
Secrete large number of hormones
Regulate gastrointestinal function

19. Functions of small intestine
Activation of trypsinogen
By enterokinase secreted by small intestine
mucosa

20. Functions of small intestine
 Water balance
 Amount of juice presented to the small intestine comes to about
9L.
 Out of this 2 L from dietary sources
 7L from gastrointestinal juices
 Only 1-2 liters reach colon rest is absorbed in the small intestine

21. Functions of small intestine
Mucus
Secreted by goblet cells
Secreted by Brunner glands
Protects intestinal mucosa

22. Functions of small intestine
Hemopoietic function
Vitamin B 12 is absorbed from small intestinein
the presence of intrinsic factor
Deficient absorption of vitamin B12 causes
pernicious anemia

23. Regulation of small intestine
secretion
Neural regulation
Hormonal regulation

24. Regulation of small intestine
secretion
 Neural regulation
 Contact of chyme with small intestine glands increases
secretion through a local reflex.
 Para sympathetic stimulation increases secretion and
produce vasodilation in the gland
 Sympathetic stimulation has no effect on small intestine
secretion

25. Regulation of small intestine
secretion
Hormonal regulation
Secretin, gastrin, CCK, glucagon and calcitonin
increases secretion of small intestine juice
Enterocrinin specifically increases secretion from
small intestinal glands

26. Large intestine
Extends from ileocecal valve to anus
100 cm in length during life
Mucosa is smooth and no villi
Fibers of muscularis externa in colon are collected
into three longitudinal bundles, teniae coli.

27. Large intestine
These bands are shorter than rest of the colon
Columnar epithelial cells and goblet cells secrete
mucus
Secretion is thick, viscous, alkaline
pH around 8

28. Functions of Large intestine
Lubrication of fecal matter by mucus secreted by
large intestinal glands

29. Functions of Large intestine
 Absorption – large intestine absorbs water, electrolytes,
vitamins, short chain fatty acids, glucose, certain drugs like
steroids, sedatives, anesthethetics.
 Drugs are given as enema especially in children
 Most of the absorption occurs in the proximal half of large
intestine – absorptive colon
 The distal portion of colon – storage colon

30. Functions of Large intestine
Synthesis of vitamins – some of the bacteria of
large intestine synthesize vitamins like B complex,
vitamin K, folic acid, etc. and these vitamins are
absorbed from the colon in significant amounts.

31. Functions of Large intestine
Certain bacteria in the intestine can even digest
the cellulose.

32. Functions of Large intestine
Formation and storage of fecal matter – Large
intestine converts 1-2 L of isotonic chyme that
enters the colon each day into about 200-250 ml
of semisolid feces.
Feces is stored in colon

33. Functions of Large intestine
Excretory function – Large intestine excretes heavy
metals like lead etc through feces.

34. Dietary fiber
Includes all ingested food that reaches large
intestine in an unchanged state
It includes cellulose, hemicelluloses, lignin, gums,
algal polysaccharides etc present in the vegetables
in the diet.

35. Dietary fiber
Dietary fibers are not digested in the human digestive
tract
It adds bulk to the stool
Initiates defecation reflex
If amount of dietary fiber is less, it decrease the bulk
of stool and cause constipation

36. Movements of small intestine
Movements of small intestine are
MMC
Segmentation contractions or mixing contractions
Tonic contractions
Peristalsis
Movements of villi

37. MMC
Migrating motor complex
Occur during fasting
It starts in the stomach
It keeps GIT clear of bacteria, undigested material,
desquamated cells and secretions.
It is controlled by hormone motillin.

38. Segmentation contractions
Concentric ring like contractions
Contractions of circular muscle
Appears at regular intervals
Divides small intestine lumen into segments.
Length of one contraction is about 1 cm

39. Segmentation contractions
 Length of one contraction is about 1 cm
 Each set of contractions divides small intestine into spaced
segments
 These contractions disappear and replaced by other set of
contractions
 Areas of relaxation become areas of contraction and vice
versa

40. Tonic contractions
Prolonged contractions that isolate one segment
of intestine from another
The length of small intestine is less during life due
to this tonic contractions

41. Functions of segmentation and Tonic
contractions
Mixes food thoroughly with digestive juices
Assist in active absorption
Has a massaging effect on blood vessels and
lymphatics

42. Peristalsis
Reflex propulsive movement of GIT
Initiated when gut wall is stretched
Occurs in all parts of GIT from esophagus to rectum
Help to move the chyme forward towards large
intestine

43. Peristalsis
The peristalsis reflex and the anal ward direction
of movement of peristalsis is called law of
intestine.

44. Factors influencing Peristalsis
Stimulating factors
Stretch of gut wall
Gastro enteric reflex- distension of stomach sends
impulses through the myenteric plexus from stomach
down along the wall of small intestine
Para sympathetic stimulation

45. Factors influencing Peristalsis
Inhibiting factors
Sympathetic stimulation
Hormones like secretin, glucagon etc

46. Movements of intestinal villi
Small intestine is lined by numerous villi
Villi exhibits two types of movements
Lashing movements or swaying movements
Lengthening and shortening movement
These movements enhance mucosal blood flow and
lymph flow

47. Diseases of small intestine
Intestinal obstruction
Localized obstruction of small intestine
Due to spasm growths or worms
Causes severe pain- intestinal colic
The segment of intestine above the point of
obstruction dilates and filled with fluid and gas

48. Diseases of small intestine
 Mal absorption syndrome
 Major function of small intestine is digestion and absorption of
food
 If more than 50 % of small intestine is removed
 It leads to malnutrition
 Effect varies with cause and type of food that is not absorbed

49. Diseases of small intestine
If it is protein, it leads to body wasting, edema
If it is fat, it leads to steatorrhea and vitamin
deficiency
Especially vitamin K leading to bleeding disorders

50. Movements of large intestine
Segmentation contractions
Peristalsis
Mass action contraction

51. Movements of large intestine
Segmentation contractions and peristalsis are
similar to those occurring in the small intestine
Segmentation contractions mixes the contents of
colon and facilitates absorption
Peristalsis waves propel contents towards rectum

52. Movements of large intestine
 Mass action contraction or mass peristalsis
 Occurs only in colon
 Simultaneous contraction of smooth muscle over large
areas
 Frequently occurs in the transverse and descending colon
 It helps initiation of defecation reflex

53. Transit time in GIT
First part of test meal reaches cecum in 4 hours
All undigested particles enters colon in 8 hours and
reaches pelvic colon in 12 hours
70% of undigested matter is expelled in 72 hours
But it takes more than a week for total removal of all
undigested matter from GIT

54. Defecation
 Act of expelling fecal matter
 Mass action contraction helps for this
 Fecal matter is forwarded and stored in the pelvic colon not in rectum
 Due to peristalsis rectum gets filled with fecal matter
 When rectal pressure reaches about 55mmHg, desire for defecation
occurs.
 Both internal and external sphincters relax and fecal matter is expelled
out.

55. Defecation
Spinal reflex
Voluntarily initiated by relaxing the external
sphincter
Contracting the abdominal muscles

56. Abnormalities of Defecation
Constipation
Difficult defecation
Dehydration
Decrease in dietary fiber
Diseases like hypothyroidism

57. Abnormalities of Defecation
Constipation
causes
Decreased motility of intestine
Feces will be dry and hard of excess water
reabsorption as feces remain longer time in colon

58. Abnormalities of Defecation
 Diarrhea
 Increase in the frequency, volume and fluid content of stool
 Increased motility of intestine
 Increases secretion of water and electrolytes into lumen
 Decreased absorption from intestine

59. Abnormalities of Defecation
Diarrhea
Typhoid fever
Cholera
Gastro enteritis
Severe diarrhea leads to dehydration, hypovolemia,
electrolyte imbalance.