Which part of the stomach will have more forceful, more frequent contractions?
The part of the stomach that is most caudad, closest to the pylorus.
Which nerve innervates most of the muscles of mastication?
The trigeminal nerve / Cranial nerve V.
What is the maximum frequency of slow waves in the stomach?
3 – 5 waves per minute
What hormone regulates the migrating myoelectric complex?
What three things given increase action potentials and force of contraction in the stomach?
Parasympathetic activity (acetylcholine).
What cells are thought of as of the pacemaker for the slow waves of the G.I. system?
Where are they located?
Interstitial cells of Cajal.
In the myenteric plexus (Auerbach's) between the outer and inner layers of the muscularis externae.
What are the three mechanisms for negative feedback of the duodenum to the stomach – decreasing gastric emptying?
Acid in the duodenum stimulates secretin which inhibits gastrin – thereby inhibiting gastric emptying.
Fats in the duodenum stimulate cholecystokinin and glucose-dependent insulinotropic peptide – which directly inhibit stomach motility.
Hypertonicity in the duodenum (overfull duodenum) directly inhibits gastric emptying through an unknown hormone.
What three things given decrease frequency of action potentials and force of contraction of the stomach?
Sympathetic activity (norepinephrine).
Glucose-dependent insulinotropic peptide (GIP).
What is released by enterochromaffin -like cells to initiate peristalsis?
What is the receptor for that molecule?
Enterochromaffin -like cells produce serotonin.
This serotonin binds to receptors on intrinsic primary afferent neurons.
Which nerves transmit afferent signal in the vomiting reflex?
The vagal afferents or the sympathetic afferents.
What part of the central nervous system controls the involuntary swallowing reflex?
The swallowing center of the medulla.
Which neurotransmitters are released in the circular muscle behind the bolus during peristalsis?
Excitatory transmitters acetylcholine, substance P, and neuropeptide Y.
(Note that these transmitters are inhibited in the longitudinal muscle behind the bolus)
Which part of the stomach is less responsible for the mixing of food, and more responsible for accommodation of food?
The orad region.
What is receptive relaxation?
The phenomenon by which the orad region of the stomach relaxes receptively with the lower esophageal sphincter.
What part of the central nervous system coordinates the chewing reflex?
What is the migrating myoelectric complex?
The migrating myoelectric complex is a sort of housekeeping that occurs during fasting. It consists of large bursting peristaltic contractions throughout the stomach (including the orad region, which is normally quiet).
Which nerves carry afferent sensory information to the medullary swallowing center?
The glossopharyngeal and vagus nerves.
How do slow waves generate a contraction?
The depolarization occurs in a slow arc, and when it reaches threshold, action potentials occur. These action potentials cause contraction.
Where's the vomiting center of the brain located?
In the medulla
What is different about the slow waves and their relationship with muscle contraction in the stomach vs. the small intestine?
Slow waves in the small intestine do not themselves initiate contractions, unlike in the stomach.
In the small intestine they can only set the frequency of contractions.
What are the steps of the vomiting reflex physically?
Reverse peristalsis, forced inspiration, movement of the larynx, lower esophageal sphincter relaxation, closure of the glottis, and ultimately a forceful expulsion of gastric contents.
What is the slow wave frequency in the duodenum, jejunum, and ileum?
What neurotransmitter causes the lower esophageal sphincter to relax in response to an approaching food bolus?
What releases this neurotransmitter?
Vasoactive intestinal peptide.
Fibers of the vagus nerve.
What initiates the primary and secondary peristaltic waves in the esophagus respectively?
The primary peristaltic wave of the esophagus is initiated by the swallowing reflex of the medulla.
The secondary peristaltic wave is initiated in the case that the primary peristaltic wave does not clear the esophagus of food, and is initiated by the myenteric (Auerbach's) plexus.
What are the steps involved in the pharyngeal phase of swallowing?
First, the soft palate is pulled upwards moving the epiglottis.
Then the upper esophageal sphincter relaxes.
Then the pharynx initiates a peristaltic wave of contractions to push food into the esophagus.
What nerves of the parasympathetic nervous system are responsible for which portions of the large intestine?
The vagus nerve is responsible for the cecum, ascending colon, and transverse colon.
The pelvic nerves are responsible for the descending colon, sigmoid colon, and rectum.
What neurotransmitters are released in the circular muscle in front of the bolus during peristalsis?
Inhibitory transmitters vasoactive intestinal peptide, and nitric oxide.
(Note that these are what are inhibited in the longitudinal muscle in front of the bolus.)
How is peristalsis different in the large intestine than the small intestine?
The large intestine utilizes mass movement, which occurs only one to three times per day
What is the function of cholecystokinin on the orad region of the stomach?
Decreases gastric contractions and increases gastric distensibility.
Which nerve controls the internal anal sphincter?
Which nerve controls the external anal sphincter?
Internal anal sphincter – pelvic splanchnic nerve.
External anal sphincter – pudendal nerve.