Swallowing_intestinal motility

Question 1

Oral Phase

Answer 1

Voluntary

tongue pushes food against touch receptors on pharynx—> MO—>initiates swallowing reflex

Question 2

Pharyngeal Phase

Answer 2

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

Question 3

Esophageal phase

Answer 3

after UES closes, LES begins to relax
MO initiates peristaltic wave below UES
Distention initiates secondary peristalsis (only if primary wave not sufficient)

Question 4

UES

Answer 4

striated muscle that is regulated by the swallowing center via cranial nn.
highest resting pressure of all GIT sphincters

closes during inspiration

Question 5

LES

Answer 5

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)

Question 6

Achalasia

Answer 6

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

Question 7

GERD

Answer 7

reduction of pressure in LES—>reflux of gastric juice—>erosion of esophageal mucosa

Question 8

Receptive relaxation of stomach

Answer 8

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

Question 9

Things that promote Gastric mixing

Answer 9

1) Distension of stomach by chyme
2) ENS—>Ach and Sub P
3) Gastrin

Question 10

Things that inhibit gastric mixing

Answer 10

1) Presence of FA, ACIDIC CHYME, AAs or distension of duodenum
2) Intrinsic and extrinsic neural response
3) CCK, secretin, GIP

Question 11

Increasing gastric contractility

Answer 11

Ach and Gastrin increase the amplitude of depolarization and the duration of depolarization=increased contractility

Question 12

decreasing gastric contractility

Answer 12

NE hyperpolarizes the membrane, making threshold harder to be reached

decreases amplitude of slow waves—>decreased contractility

Question 13

Gastric emptying

Answer 13

occurs when the pyloric sphincter is open
rate depends on meal content
liquid>carbs>protein>fat
Isotonic>hypertonic/hypotonic

Question 14

Migrating myoelectric complex

Answer 14

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

Question 15

Reverse peristalsis

Answer 15

SI—>pyloris
PS and stomach relax—>abdominal muscles contract—>pylorus and antrum contract —>LES relaxes—>UES relaxes

(retching is when UES remains closed)

Question 16

Segmentation

Answer 16

postprandial period
alternating contractions of circular smooth muscle to mix chyme with digestive enzymes
maximizes digestion and absorption

Question 17

Peristalsis

Answer 17

postprandial: coordinated propulsive contractions of circular smooth muscle

Relaxation in front of bolus: VIP and NO
contraction behind bolus: ACh and substance P

Question 18

Haustrations

Answer 18

short duration contractions (8sec)
circular m. mixing contractions (like segmentation)
no propulsion

Question 19

long duration contractions

Answer 19

20-60sec
teniae coli
coxing contractions that also propagate in both directions

Question 20

mass movements

Answer 20

high amp propagating contractions
sweep length of colon
1-3/day
high individual variability

Question 21

neural control of colonic motility

Answer 21

Vagus via ENS—>increased contractions in proximal colon
Pelvic nn. via ENS—>increased contractions in distal colon
SNS—>inhibits motility

Question 22

Defecation reflex

Answer 22

requires extrinsic neural input via pelvic nn.

distension of the rectum—>rectosphincteric reflex (via VIP and NO)—>relaxation of IAS—>constriction of EAS

Question 23

postponed defecation

Answer 23

occurs as a result of accommodation of the rectum
IAS contracts
EAS relaxes

Question 24

defecation

Answer 24

voluntary relaxation of EAS
Contraction of abdominal muscles
relaxation of pelvic muscles

Question 25

IBS

Answer 25

visceral hypersensitivity due to sensitization of afferent neural pathways: respond abnormally to stimuli: idiopathic

Crohn’s and ulcerative colitis