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.
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
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
14.
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
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
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
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
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
38. Enterogastric Reflexes
Initiate when there is
Duodenal distension
Chyme is acidic
Chyme hyper osmolality
Irritation of duodenum
Protein products in chyme
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
43.
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.
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
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
54.
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)