This document describes the structure and function of the gastrointestinal tract. It discusses digestion beginning in the mouth through the stages of swallowing. It describes the movements and regulation of the stomach, small intestine, and large intestine that propel and mix food contents. Key functions and control mechanisms of various structures like the lower esophageal sphincter, ileocecal valve, and anal sphincters are summarized. The reflex pathways involved in defecation are also outlined.

1. GASTROINTESTINAL TRACT

3. Digestion in mouth
Two types:
Mechanical: By mastication
Chemical: By Saliva

4. MASTICATION
 Presence of food bolus in mouth
 reflex inhibition of muscles of mastication

 drooping of lower jaw
 stretch of jaw muscle
 rebound contraction
 jaw raised up
 closure of teeth
compression of bolus again………….

5. REGULATION OF
MASTICATION
 It is under nervous control.
 Muscles of chewing are innervated by motor
branch of trigeminal( 5th cranial n )
 Controlled by nuclei in the brain stem & reticular
area, areas of hypothalamus, amygdala ,sensory
areas for taste and smell

6. SWALLOWING
 Involves the coordinated activity of the tongue,
soft palate, pharynx, esophagus and 22 separate
muscle groups

8. STAGES OF SWALLOWING
 1)VOLUNTARY STAGE
 2)PHARYNGEAL STAGE
 3)ESOPAHGEAL STAGE

10. VOLUNTARY STAGE OF
SWALLOWING
FOOD IN MOUTH
MASTICATION
VOLUNTARILY SQUEEZED AND ROLLED
BY TONGUE AGAINST PALATE
PUSHED IN PHARYNX

12. PHARYNGEAL STAGE
 RECEPTOR:
 Ring around pharyngeal opening tonsillar pillars
 AFFERENT:
 Trigeminal nerve,
 Glossopharyngeal nerve
 CENTRE:
 NTS+medulla+lower pons=swallowing centre
(nucleus of the tractus solitaries)
 EFFERENT:
 Cranial nerve 5,9,10,12,superior cervical nerve

13. STEPS
SOFT PALATE IS PULLED UPWARD
PALATOPHARYNGEAL FOLDS APPROXIMATE
VOCAL CORDS ARE APPROXIMATED
LARYNX IS PULLED UPWARD AND
FORWARD
UPPER ESOPHAGEAL SPHINCTER
RELAXES
PHARYNGEAL MUSCULAR WALL
CONTRACTS
PERISTALSIS

15. Nervous control
SENSORY 5th and 9th nerves
Tractus solitarious and swallowing centre
Motor impulses from 5th,9th,10th,12th nerves
Pharynx and upper esophagus

16. EFFECT OF PHARYNGEAL STAGE
ON RESPIRATION
 <6 seconds
 Interrupt respiration for a very shorter time hardly
noticeable
 Swallowing centre inhibits respiratory centre

17. ESOPHAGEAL STAGE
 Conduct food from pharynx to stomach
 1)primary peristalsis
 2)secondary peristalsis

18. PRIMARY PERISTALSIS
 Continuation of pharyngeal peristalsis
 8-10 sec
 In standing position 5-8 sec(effect of gravity)

19. SECONDARY PERISTALSIS
 Starts by distension of esophagus by retained
food by
1.Intrinsic neural circuit by myenteric plexus
2.Reflex start from pharynx by 10th nerve to
medula . From medulla to esophagus by 9th and
10th nerve
 Receptive relaxation of stomach to receive food .

20. LOWER ESOPHAGEAL
SPHINCTER
 At lower end of esophagus
 Tonically constricted
 Wave of peristalsis opens LES (lower esophageal
sphincter)
 Achalasia (failure of LES to relax and open ) .
 IMPORTNACE:
 Prevents reflux
 Usually its tightly closed so that even air cannot
pass through it

21. PREVENTION OF ESOPHAGEAL
REFLUX
 1)tonic constriction of LES
 2)valve like closure of distal end of esophagus

22. WRITE MOTOR FUNCTIONS OF
STOMACH
 1)Storage
 2)mixing
 3)emptying

24.  ANATOMICAL DIVISION:
 1)Body
 2)antrum
 PHYSIOLOGICAL DIVISION:
 1)orad
 2)caudad

25. STORAGE FUNCTION OF
STOMACH
ENTRY OF FOOD
ARRANGMENT OF FOOD IN
CIRCLE(rip)
STOMACH STRETCHES(Rugae
flattens)
VAGOVAGAL REFLEX(stomach to brain stem back to
stomach
TONE OF STOMACH WALL
DECREASES

26.  Vagovagal eflex:
Afferents carried by vagus nerve-----centre is
brainstem----effernt by vagus---- it causes
relaxation of muscles

27. MIXING OF FOOD
ENTRY OF FOOD+MIXING WITH GASTRIC
SECRETIONS
WEAK PERISTALTIC CONSTRICTOR WAVES
(MIXING WAVES,BASIC ELECTRICAL
RHYTHM)
PROGRESSION
PERISTALTIC ACTION POTENTIAL DRIVEN
CONSTRICTOR RING
MIXING

28. ROLE OF CONSTRICTOR
RINGS
 DIGS IN FOOD
 PYLORUS OPENING IS SMALL (FEW ml
ONLY)
 PYLORIC MUSCLE CONTRACTS
 SQUEAZED UPSTREAM
 RETROPULSION

29. What is RETROPULSION ?
The moving peristaltic contrictive ring
+
Upstream squeezing action
=
RETROPULSION

30. CHYME
 Factors affecting DEGREE OF FLUIDITY OF
CHYME:
 1)Amount of food
 2)amount of water
 3)amount of secretions
 4)degree of digestion
 Murky semi fluid paste which goes from stomach
to duodenum.

31. HUNGER CONTRACTIONS
 STIMULUS:
 12-24 hrs after meal
 Low BSL
 Starvation(intensity increases in 3-4 days then
weakens)
 HIGHER IN YOUNG HEALTHY PEOPLE(HIGH
TONUS)

32. Stomach Emptying
20% of time peristaltic contraction are strong
Ring like constrictions
Progression from body to antrum
Pinches food from body and add it to chyme in
Antrum

33. Pyloric Pump
Peristaltic waves in stomach also provides pumping
action in addition to mixing are called pyloric
pump

34.  Tonic contraction of pyloric sphincter keeps it
almost but not completely closed. Opening is
large enough to allow fluid to pass but doesn't
allow thick chyme

35. Regulation of Emptying
 Gastric Factors: promote emptying
 Duodenal factors: inhibits emptying
 Extrinsic factor: emotions,intense pain,decreased
glucose utilization in hypothalamus

36. Gastric Factors(promote)
1.Food volume:
Stretching of wall elicits myenteric reflexs which
i.Increases pyloric pump activity
ii. Inhibits pylorus
2.Gastrin hormone:
Enhances pyloric pump activity
.Carbohydrates are emptied more quickly from
stomach as compared to protein and fats

37. Duodenal Factors(Inhibit)
 1.Enterogastric Reflexes
 1.Hormones
They inhibit pyloric pump and increase pylorus tone

38. Enterogastric Reflexes
Initiate when there is
 Duodenal distension
 Chyme is acidic
 Chyme hyper osmolality
 Irritation of duodenum
 Protein products in chyme

39. Hormones
 CCK (Cholecystokinin)
 GIP (Gastric inhibitory polypeptide)
 Motilin

40. Extrinsic factors
Emotions
 Works through ANS
 Varies from person to person
 Sadness,fear…usually decreases motility
 Anger,aggresion…usually increases
Intense pain decreases by stimulating sympathetics

41. Small intestine movements
 Mixing Movements also called Segmentations.
(segmentation involves the contraction and relaxation of segments of
circular smooth muscle in the intestines. Segmentation contractions move
chime in both directions.)
 Propulsive Movements

42. MIXING MOVEMENTS
 CHYME
 DISTENSION OF SMALLINTESTINE
 LOCALIZED CONCENTRIC CONTRACTIONS at
intervals
 SEGMENTATIONS(Divides intestine into spaced
segments)
 One segment relaxes and other contracts
 CHOPS CHYME 2-3 TIMES / min

44.  Maximum frequency depends on slow wave
frequency
 Duodenum 12/min
 Ileum 8-9/min
 Caused by slow waves reaching threshold to
cause action potential….slow waves stimulated
by distension, gastrin(ileum) and extrinsic
nerves.

45. PROPULSIVE MOVEMNTS
 CHYME
 PERISTALTIC WAVES
 PROPELS FOOD(0.5-2cm/min)
 Net movemnt =1 cm/min
 Chyme takes 3-5 hrs till ileocecal valve

46. REGULATION OF
PERISTALSIS
NERVOUS HORMONAL
Myenteric plexus enhances motility:
REFLEXES: gastrin
1)gastroenteric reflex CCK,insulin,motilin
2)gastroileal reflex serotonin
inhibits motility
secretin
glucagon

47. PERISTALTIC RUSH
“powerful rapid peristalsis”
CAUSE:
Irritation (e.g diarrhea)
REGULATION:
EXTRINSIC:
ANS and brain
INTRINSIC:
Myenteric plexus
Reflexes within the gut

48.  MECHANISM:
 Powerful peristaltic contractions travel long
distances rapidly towards colon
 IMPORTANCE:
 Sweeps irritative chyme from intestine
 Relieves small intestine from irritation

49. ILEOCECAL VALVE

50. FUNCTIONS
 1)prevents backflow of fecal content from colon to
ileum
 2)valve like mechanism
 3)ileocecal sphincter
 4)gastroileal reflex
 5)facilitate absorption by increasing time

51. CONTROL OF ILEOCECAL
SPHINCTER
 FACTORS:
 1)Distension of cecum
 2)irritation eg appendicitis
 NERVOUS REGULATION:
 Myenteric plexus
 Extrinsic autonomic nerves(prevertebral
sympathetic ganglia)

52. MOVEMENTS OF COLON
 PRIMARY FUNCTION
 ABSORPTION STORAGE
 (PROXIMAL) (DISTAL)

53. MOVEMENTS of colon
 MIXING PROPULSIVE
 (HAUSTRATIONS) (MASS MOVEMENTS)
 Large circular distension
 Muscle constrictions
 (2.5 cm) constrictive ring in transverse colon
 +
 Taniae coli >20cm ahead of constriction,colon
loses
 = haustrations
 Bag like sacs(3

 dug into and rolled Contraction (30sec)
relaxation(3min)
 Over mechanism
 propels feces as mass
absorption+minor propulsion

55.  MIXING MOVEMENTS
 Absorption
 Minor forward propulsion
 MASS MOVEMENTS:
 1-3 times per day
 15 min after breakfast
 Contractions – 30 sec
 Series persists for 10-30 min
 Modified type of peristalsis
 Responsible for desire to defecate

56. REFLEXES RESPONSIBLE FOR
CAUSES OF MASS MOVEMENTS
 1)Gastrocolic reflex
 2)Duodenocolic reflex
 3)Irritation(ulcerative colitis)

57. DEFECATION
STIMULUS:
mass movement
Forces feces in rectum
Desire for defecation
Reflex contraction of rectum relaxation of anal
sphincter

58.  HOW FECES ARE PREVENTED TO ENTER
RECTUM:
 Angulation of sigmoid colon
 Weak functional sphincter at junction of sigmoid
colon and rectum

59. ANAL SPHINCTERS
PROPERTIES INTERNAL ANAL
SPHINCTER
EXTERNAL ANAL
SPHINCTER
LOCATION
LIES IMMEDIATELY
INSIDE
ANUS
SURROUNDS
INTERNAL SPHINCTER
AND DISTALLY
TYPE OF MUSCLE SMOOTH MUSCLE SKELETAL MUSCLE
CONTROL INVOLUNTARY VOLUNTARY(pudendal
nerve)

60. DEFECATION REFLEXES
 1)intrinsic reflex
 2)parasympathetic reflex

61. INTRINSIC REFLEX
 FECES IN RECTUM
 DISTENSION
 AFFERENT SIGNALS VIA MYENTERIC PLEXUS
 PERISTALTIC WAVE GENERATION
 (DESCENDING COLON,SIGMOID COLON,RECTUM)
 FORCES FECES TOWARDS ANUS
 INTERNAL ANAL SPHINCTER RELAXED(INHIBITORY SIGNALS
FROM MYENTERIC PLEXUS)+EXTERNAL SPHINCTER
RELAXED voluntarily

 DEFECATION

62. PARASYMPATHETIC REFLEX
 FECES IN RECTUM
 NERVE ENDINGS IN RECTUM GET
STIMULATED
 AFFERANT(sensory)
 SPINAL CORD
 PELVIC PARASYMPATHETIC NERVES
 DESC,SIG,RECTUM,ANUS,INTERNAL
SPHINC
 INTRINSIC REFLEX becomes stronger


64. STEPS
Taking deep breath
Closure of glottis
Contraction of abdominal wall muscles
Relaxation and movement of pelvis
floor downward

65. COMPOSITION OF FECES
 Three-fourths water
One-fourth solid matter
 30% dead bacteria
 10-20% fat
 10-20% inorganic matter
 2-3% protein
 30% undigested roughage (e.g. bile pigment,
sloughed epithelial cells)