GI 4 Flashcards
Is swallowing initiation voluntary or involuntary?
voluntary
3 Phases of Swallowing
- Oral
- Pharyngeal
- Esophageal
Oral phase
tongue push bolus to soft palate, triggers swallowing reflex
Which of the three phases of swallowing is under voluntary control?
oral phase
Pharyngeal phase
propel food bolus from mouth through pharynx to esophagus
Esophageal phase
move bolus through esophagus to stomach
Peristalsis
coordinated series of muscle constrictions and relaxations to create propulsive motility of the GI tract
Area of constriction
part of peristalsis created by contractions of the inner circular muscle
Dilation
part of peristalsis created by contractions of the outer longitudinal muscle
What innervates striated muscle of the esophagus?
direct innervation by somatic motor fibers of the vagus nerve
What innervates smooth muscle in the esophagus?
visceral (autonomic) motor fibers of the vagal nerve via myenteric plexus
Functions of the Upper Esophageal (Cranial) Sphincter
deliver bolus to stomach under control of swallowing reflex; prevent air and reflux from entering upper esophagus
Functions of the Lower Esophageal (Cardiac) Sphincter
prevent gastroesophageal reflux
Sensory Nerve function in Control of Swallowing
in pharynx and esophagus, detect distention and low pH and communicate to the medulla (can also supplement the myenteric plexus)
Medulla function in Control of Swallowing
tell respiratory center (also in medulla) to pause respiration; communicate with vagal nuclei to send motor signals
Megaesophagus
generalized esophageal dilation and hypoperistalsis
Achalasia
lower esophageal sphincter fails to undergo relaxation so contents can’t get into stomach
Treatment for Megaesophagus?
Bailey chairs
Functions of the Stomach (3)
- Temporary food storage
- Process food into a fluid consistency
- Release fluid into the intestine at a controlled rate
4 Parts of the Stomach
- Cardiac part
- Fundus
- Body
- Pylorus
Proximal Region of the Stomach Function
store ingested food, tonic contractions
Distal Region of the Stomach Function
break up, mix, and propel food; phasic contractions
Fundic Accomodation
fundus expands in response to increased gastric pressure to prevent reflux
retropulsion
occurs when peristaltic wave hits pyloric sphincter and ingesta is crushed and pushed back towards proximal stomach
3 Locations that can trigger Fundic Accomodation
- Mouth/Pharynx
- Stomach
- Small Intestine
Fundic Accommodation at the Mouth/Pharynx
chewing/swallowing triggers vagovagal reflex; motor neuron releases ACh at the myenteric plexus, which in turn triggers the release of inhibitory NTs (NO and VIP) causing relaxation of the proximal stomach to decrease gastric pressure
Fundic Accommodation of the Stomach
sensory neurons of the enteric nervous system detect stretch of the stomach wall, also causes release of NTs for additional relaxation of the proximal stomach; can also signal back to CNS
Fundic Accommodations of the Small Intestine (2)
components of digestive products (fats, proteins) signal the release of CCK from enteroendocrine cells and tells a sensory neuron back to the dorsovagal complex to trigger one of the other responses; stretch of small intestine can also directly cause the release of NO and VIP
Enterogastric Reflex
feedback loop due to a signal from the small intestine to cause an effect in the stomach
What three environmental aspects in the duodenum could inhibit stomach emptying via the enterogastric reflex?
- Low pH
- High osmolality
- Presence of Fat
Migrating Motor Complex
takes effect during fasting (interdigestive phase) to clear all the residue in the GI tract, contractions throughout stomach with a wide open pyloric sphincter and relaxed duodenum
Hormone involved in the Migrating Motor Complex?
Motilin
Problems if gastric emptying is too slow?
vomiting, loss of appetite, early satiety, gastric ulcers; often due to obstructions at the gastric outlet (cancer, peptic ulcer disease) or problems with motor events in distal stomach
Problems if gastric emptying is too fast?
diarrhea, duodenal ulcers
