Gastrointestinal function and esophageal motility

what is the primary neural mechanism that controls GI function?

the enteric nervous system, subclustered into submucosal (meissner’s) plexus and myenteric (auerbach’s) plexus

levels of secretion in different areas of the GI tract: little to no secretion of hormones in the _________

colon

stimulus for gastrin release

proteins, ACh

gastrin targets

enterochromaffin like cells (ECL) and parietal cells of gastric corpus

gastrin effects

tells ecl to secrete histamine and parietal to secrete H+

match gastrin and CCK to their receptors

They both can bind both, but gastrin prefers to bind to CCK2 way more than CCK does, and CCK prefers to bind CCK1 way more than gastrin does

what cells secrete CCK

I cells

stimulus for CCK release

fatty acids and proteins

targets of CCK

vagal afferent terminals and pancreatic acinar cells

effects of CCK

inhibits gastric emptying and H+ secretion, stimulates pancreatic secretion/gallbladder contractions, and inhibits food intake

secreted by which cells

s cells of the duodenum

secretion stimulus

protons, low intraluminal pH

secretin targets

vagal afferents terminals and pancreatic acinar cells

secretin effect

stimulate pancreatic secretions (h2o and hco3)

glucose dependent insulintropic peptide (GIP) secreted by

k cells of duodenum and jejunum

GIP stimulus

fatty acids/glucose

GIP target

pancreatic beta cells, GI, adipose tissue

GIP effects

inhibit gastric secretion and stimulate releases of insulin from the pancreas

motilin secreted by

M or Mo, entero-endocrine cells of the duodenum/jejunum

motilin stimulus

fasting

motilin targets

stomach and small intestine

motilin effects

stimulates the migrating motor complex; MMC: gastric motility, intestinal motility

name the six sphincters of the gi tract

upper esophageal, lower esophageal, pyloric, ileocecal, internal anal, external anal

relazation of the LES is mediated by what nerve and compound

vagus nerve via VIP and intrinsic properties of smooth muscle

what is peristalsis

coordinated series of muscle movements that help move materials along the esophagus, in addition to gravity

three phases of swallowing

oral phase, pharyngeal phase, esophageal phase

oral phase of swallowing

push food back toward pharynx and activates receptors that initiate swalloing reflex

pharyngeal phase of swallowing

relax the UES and food is propelled from mouth through pharynx to esphagus

esophageal phase of swallowing

food is propelled along esophagus to stomach via the peristaltic waves (primary and secondary)

describe peristaltic wave

striated muscles contract within 1-2 seconds, middle third of esophagus withing 3-5, and lower third within 5-8

peristalsis is stimulated by

distension. mechanoreceptors transmit signal to dorsal vagal complex, activates somatic and vagal efferents which act on muscles or nerves of ENS.

ACH: from ENS above the food to induce contractions

NO released below the food to induce relaxation

relaxing of the LES

carefully coordinated with peristalsis.

NO and VIP released to help sphincter relax

dysphagia

abnormal swallowing reflex or structures involved. difficulty swallowing.

can’t propel bolus with enough force

can be seen after stroke

could be not enough saliva/lubrication

risks of dysphagia

aspiration, malnutrition, choking

achalasia

bfailure to relax

LES not entirely open

dysfunction in the sphincter region, could be autoimmune

Lack NO synthase responsible for NO

possibly decreased VIP

Barrett’s esophagus

strat squamous replaced by columnar epi

metaplastic

chronic injury from GERD

increased risk for esophageal cancer