Swallowing_intestinal motility Flashcards
Oral Phase
Voluntary
tongue pushes food against touch receptors on pharynx—> MO—>initiates swallowing reflex
Pharyngeal Phase
Involuntary food propelled from pharynx to eso soft palate blocks off nasopharynx epiglottis blocks off trachea UES relaxes while peristaltic wave pushes bolus thru respiration is inhibited
Esophageal phase
after UES closes, LES begins to relax
MO initiates peristaltic wave below UES
Distention initiates secondary peristalsis (only if primary wave not sufficient)
UES
striated muscle that is regulated by the swallowing center via cranial nn.
highest resting pressure of all GIT sphincters
closes during inspiration
LES
Smooth muscle
allows coordinated movement of food into stomach, while preventing gastric reflex
Tonically contracted (intrinsim myogenic properties+ Ach)
Relaxed when acted upon by vagus n. (VIP and NO)
Achalasia
absence of relaxation of LES—>megaesophagus just proximal to the LES —>dysphagia
also caused by impaired peristalsis in the distal 2/3
possible loss of inhibitory neurons to LES (VIP and NO-which cause relaxation)
Tx=reduce LES pressure with gravity
GERD
reduction of pressure in LES—>reflux of gastric juice—>erosion of esophageal mucosa
Receptive relaxation of stomach
initiated by swallowing
LES and stomach relax, allows food to enter and be stored: no increase in pressure in the stomach despite increased volume
**mediated by vasovagal reflex (VIP)
***Vagotomy—>rapid increase in pressure
only works to a threshold, after which pressure increases
Things that promote Gastric mixing
1) Distension of stomach by chyme
2) ENS—>Ach and Sub P
3) Gastrin
Things that inhibit gastric mixing
1) Presence of FA, ACIDIC CHYME, AAs or distension of duodenum
2) Intrinsic and extrinsic neural response
3) CCK, secretin, GIP
Increasing gastric contractility
Ach and Gastrin increase the amplitude of depolarization and the duration of depolarization=increased contractility
decreasing gastric contractility
NE hyperpolarizes the membrane, making threshold harder to be reached
decreases amplitude of slow waves—>decreased contractility
Gastric emptying
occurs when the pyloric sphincter is open
rate depends on meal content
liquid>carbs>protein>fat
Isotonic>hypertonic/hypotonic
Migrating myoelectric complex
fasting:
occurs every 75-1200min (begins 2h after meal)
burst of electrical activity begins in the antrum which the spreads thru the GIT
cleans out undigested particles
PS and ileocecal sphincter are relaxed
correlated with high levels of motilin
Reverse peristalsis
SI—>pyloris
PS and stomach relax—>abdominal muscles contract—>pylorus and antrum contract —>LES relaxes—>UES relaxes
(retching is when UES remains closed)
Segmentation
postprandial period
alternating contractions of circular smooth muscle to mix chyme with digestive enzymes
maximizes digestion and absorption
Peristalsis
postprandial: coordinated propulsive contractions of circular smooth muscle
Relaxation in front of bolus: VIP and NO
contraction behind bolus: ACh and substance P
Haustrations
short duration contractions (8sec)
circular m. mixing contractions (like segmentation)
no propulsion
long duration contractions
20-60sec
teniae coli
coxing contractions that also propagate in both directions
mass movements
high amp propagating contractions
sweep length of colon
1-3/day
high individual variability
neural control of colonic motility
Vagus via ENS—>increased contractions in proximal colon
Pelvic nn. via ENS—>increased contractions in distal colon
SNS—>inhibits motility
Defecation reflex
requires extrinsic neural input via pelvic nn.
distension of the rectum—>rectosphincteric reflex (via VIP and NO)—>relaxation of IAS—>constriction of EAS
postponed defecation
occurs as a result of accommodation of the rectum
IAS contracts
EAS relaxes
defecation
voluntary relaxation of EAS
Contraction of abdominal muscles
relaxation of pelvic muscles
