Esophageal Motility And Slow Waves

Question 1

Upper esophageal sphincter (UES)

Answer 1

. Junction of pharynx and esophageal body

. Composed of striated muscle

Question 2

Esophagus body

Answer 2

. Located btw 2 sphincters
. Composed of both striated muscles (upper 1/3) and smooth mm.
. Body has no slow waves and no tone (flaccid)

Question 3

Lower esophageal sphincter (LES)

Answer 3

. Junction of esophageal body and stomach
. Sphincter is 4 cm long
. Upper portion is subject to intra-thoracic pressure and lower portion is subject to intra-abdominal pressure
. Composed of multi-unit circular smooth muscle w/ high myogenic tone
. Both inhibitory and excitatory neurons modulate the tone of the LES
. Along w/ crural diaphragm the LES is component of high pressure barrier btw esophageal body and stomach (esophagastric junction)

Question 4

Deglutition

Answer 4

. Swallowing
. Oral stage: voluntary, bonus food moved into oropharynx by tongue, resp. Inhibited for approx. 2 sec
. Pharyngeal stage: involuntary, begins when sensory afferent nn. Innervating oropharynx activated by bolus of food, primary peristaltic contractions of pharynx propel food through UES and into upper esophageal body
. Esophageal stage: begins as primary peristaltic wave of contraction occurs in body of esophagus and propels bolus of food through LES and into stomach

Question 5

Striated mm. Of UES

Answer 5

. Innervated directly by vagal LMNs
. Form motor endplates on striated mm.
. Release ACh

Question 6

Smooth muscle of esophagus

Answer 6

. Innervated indirectly by the vagal preganglionic neurons through myenteric neurons
. Both vagal inhibitory and vagal excitatory pathways innervate smooth m. Of esophagus

Question 7

Primary peristalsis

Answer 7

. Esophageal peristalsis is preceded by pharyngeal peristalsis
. Always follows a swallow
. Mediated by long parasympathetic neural reflex

Question 8

Secondary peristalsis

Answer 8

. Esophageal peristalsis in absence of pharyngeal peristalsis
. Initiated by distension of esophageal body by reflexes chyme
. Mediated by short and long neural reflexes
. Secondary peristalsis clears the esophageal contents

Question 9

Swallowing reflex

Answer 9

. Sensory afferent CNs innervating the oropharynx are activated by bolus of food pushed by tongue to back of mouth
. Airway closes and respiration is inhibited
. In swallowing center in brainstem, activity of efferent CNs is modulated
. Opening of UES, primary peristalsis in pharynx and striated and smooth mm. Of the body, relaxation and rebound contraction of LES
. Receptive relaxation of the fungus are all coordinated in the brainstem and mediated through efferent CN X

Question 10

How UES opens during swallowing

Answer 10

. CNS inhibition of vagal LMNs to striated m. Of UES

Question 11

Primary peristalsis due to swallowing

Answer 11

. Striated m. Of esophageal body
. CNS coordinates sequential activation of vagal LMNs to progressively distal regions of striated m.
. CNS activates parallel vagal inhibitory (NANC) and excitatory (ACh) pathways innervating all smooth mm. Regions of esophagus and fungus
. Occurs in body of esophagus (contraction), the LES opens (relaxation) and the fundic pressure drops (receptive relaxation)

Question 12

Vagal pathways after swallowing

Answer 12

. Less than 1 sec. after: All vagal inhibitory pathways innervating all smooth m. Of esophageal body, LES, and fungus are simultaneously activated
. 1-5 sec. after: vagal excitatory pathways innervating the smooth m. Of the body and the LES are sequentially activated
. Vagal preganglionic nn. That innervate progressively distal regions of the esophagus have inc. slower conduction velocities

Question 13

Esophageal body after swallow

Answer 13

. Prompt inhibition of all smooth m. Of esophageal body (deglutitive inhibition)
. Duration and magnitude of deglutitive inhibition inc. in progressively distal regions of the body due to inc. proportion of enteric inhibitory motor neurons
. Smooth m. Of body is hyperpolarzied but bc it has no basal tone there is no change in pressure
. NANC “off” depolarization participates in primary peristaltic contraction
. Cholinergic contraction and NANC “off” contraction are timed to overlap producing the total peristaltic pressure wave

Question 14

LES after swallow

Answer 14

. Opens when vagal inhibitory pathway is activated
. LES has basal tone, the prompt hyperpolarization of smooth m. Causes relaxation (opening) of sphincter
. NANS “off” depolarization participates in the rebound contraction of LES
. Rebound contraction of the :ES is timed to coincide w/ the NANC “off” contraction

Question 15

Fundus after swallow

Answer 15

. Fundus relaxes when vagal inhibitory pathway is. Activated (receptive relaxation)
. Intra-gastric pressure drops to receive swallowed food

Question 16

Mechanical dysphagia

Answer 16

. Caused by a large food bolus or luminal narrowing of esophageal body

Question 17

Motor dysphagia

Answer 17

. Caused by uncoordination or weakness of primary peristaltic contractions of esophageal body
. Difficulty initiating peristaltic reflex: damage to afferent sensory nn. Innervating the oropharynx
. Disorders of pharyngeal and/or esophageal striated m. (Skeletal m. Weakness and non-peristaltic contractions)
. Disorders of esophageal smooth m. (Paralysis of esophageal body or non-peristaltic contractions, disorders of enteric nervous system activity)

Question 18

Gastroesophageal reflux disease (GERD)

Answer 18

. Gastric contents are reflexes into esophageal body causing bothersome symptoms and/or complications
. Symptoms: due to visceral hypersensitivity to refluxed gastric contents or damage to esophageal mucosa
. Treatment: antacids, histamine receptor antagonists, proton pump inhibitors

Question 19

Gastric contents reflux into esophagus because of ____

Answer 19

. Inc. number of transient, intermittent LES relaxations that occur independent of a swallow
. Dec. LES resting pressure (damage to cholinergic enteric motor neurons)
. Hiatal hernia (portion stomach protrudes rough diaphragm into thoracic cavity
. Swallow-induced LES relaxations (assoc. w/ incomplete or defective primary peristalsis)

Question 20

How inc. number of transient intermittent LES relaxations that occur independent of swallow

Answer 20

. LES resting pressure might be normal, but LES pressure is lower than gastric pressure during long-lasting relaxations permitting reflux
. Afferents: CN X, activated by prox. Stomach distension
. Efferent: CN X inhibitory pathway to esophagus

Question 21

Slow waves

Answer 21

. Smooth mm. Of gastric antrum and SI exhibit continuous, spontaneous oscillations of resting membrane potential (slow wave) or basic electrical rhythm
. Always occurring regardless of presence or absence of smooth m. Phasic contractions or presence/absence of chyme in lumen
. Does not cause smooth m. Phasic contractions but sets frequency that AP bursts can occur in smooth m. (Phasic contractions can’t occur at higher frequency than slow wave)
. As slow wave depolarizes AP bursts can occur and smooth m. Contracts

Question 22

Likelihood that AP burst will occur in smooth m. Can be increased or decreased by ____

Answer 22

Modulating enteric or extrinsic autonomic n. Activity

. Modulating conc. Of circulating hormone or of local paracrines

Question 23

Substances that alter frequency of phasic contractions of smooth m.

Answer 23

. ACh
. Gastrin
. Motilin: exists only during interdigestive periods

Question 24

Substances that dec. frequency of phasic contractions

Answer 24

. NE/E
. Secretin
. NO
. Opioids

Question 25

Interstitial cells of cajal

Answer 25

. Pacemaker cells w/in wall of GI
. Generate slow wave in GI smooth m.
.current due to Ca handling by ICC mitochondria, may involve Cl efflux through Ca-activated Cl channels
. Spread electrical activity among other ICC and to smooth m. Cells
. In a segment of gut, the freq. of slow wave is not altered by extrinsic nn., enteric neurons, or hormones (excretion is thyroid hormones which does alter basal metabolic rate)
. Disruption of ICC network may contribute to disorders of GI motility

Question 26

Slow wave in small intestine

Answer 26

. Slow wave dec. from duodenum to jejunum to the ileum
. This helps move chyme towards the colon
. Helps move chyme towards colon (slow wave gradient akin to pressure gradient exerted by phasic contractions w/ higher pressures in duodenum and lower pressures in ileum facilitating moment towards colon

Question 27

Slow wave in large intestine

Answer 27

. No continuously present slow wave
. ICC cells present
. Slow wave is induced by distension and/or neural activity
. Frequency of slow wave inc. from ascending to transverse and descending colon to rectum
. Helps retain fecal material in large intestine

Question 28

Control smooth m. Motility is influenced by ____

Answer 28

. ICC
. Smooth muscle properties (slow waves)
. Enteric neurons
. Extrinsic autonomic nerves, hormones, and paracrines