Swallowing Flashcards
what is the inner circular layer used for
peristalsis
what is the outer longitudinal layer used for
bowel shortening
nerve fibers what nerve innervate the upper tract?
lower tract?
upper = vagus
lower = pelvic
skeletal muscles in esophagus receive what kind of fibers…and signals
post-ganglionic fibers which release Ach for contraction and inhibit Ach release for relaxation
Auerbach’s plexus
preganglionic fibers end on the enteric nerves within this plexus
located between the ICM and OLM
initiate contraction by releasing Ach and relaxation by releasing NO
upper esophagus sphincter (UES)
between oropharynx and esophagus
lower esophagus sphincter (LES)
between esophagus and stomach
pyloric sphincter
between pyloric stomach and duodenum
ileocecal valve
between ileum and cecum (start of colon)
time in esophagus
7 seconds
time in stomach
2-3 hours
time in small bowel
2-3 hours
time in large bowel
2-3 days
3 phases of swallowing
- oral (voluntary) = mastication and decision to swallow
- pharyngeal (involuntary)
- esophageal (involuntary)
oral phase of swallowing
under control of cranial nerves and consists of mastication and the decision to swallow …
with the latter initiating the pharyngeal and esophageal phases by transmission of neural signals to the
medullary swallowing center
pharyngeal phase of swallowing
4 coordinated actions designed so that the food bolus is pushed from oral cavity across a relaxed UES into the esophagus
the soft palate and epiglottic simultaneously act to occlude the nasopharynx and larynx respectively
to ensure the food doesn’t go into the airway
epiglottic closure
actuated by contraction of laryngeal muscles which elevate the larynx and lowers the epiglottis
1st step of pharyngeal phase of swallowing
soft palate elevates to occlude the nasopharynx
2nd step of pharyngeal phase of swallowing
laryngeal muscles contract to enable epiglottis to close the trachea
3rd step of pharyngeal phase of swallowing
UES relaxes to enable bolus to enter esophagus
4th step of pharyngeal phase of swallowing
pharyngeal muscles contract to initiate peristalsis to push bolus through relaxes UES into esophagus
esophageal phase of swallowing
coordinated by medullary swallowing center
sends efferent signals to organ via the Vagus Nerve
result in segments of the body of the esophagus contracting sequentially so that the luminal bolus is propulsed in a caudal direction (peristalsis)
at the same time…efferent signals from vagus results in relaxation of UES and LES areas
conditions that result in LES relaxation
- primary peristalsis
- secondary peristalsis
- transient LES relaxation
- belch reflex
- deglutitive inhibition
pressure rising in a given area of the esophagus precedes….
bolus movement through that area
once bolus enters stomach…pressure in LES
returns to pre-swallow levels to act as a barrier to reflux
primary peristalsis
initiated by a swallow
secondary peristalsis
initiated by esophageal distention by a bolus that has failed to be moved into stomach by primary peristalsis
transient LES relaxation and belch reflex
each initiated by gastric fundic distention by either food, liquid, or air
deglutitive inhibition
initiated by rapid voluntary swallowing
3 nuclei that form the major components of the medullary swallowing center
- nucleus tractus solitarius –> recepient of all sensory signals to the center
- nucleus ambiguous –> motor to skeletal muscle
- dorsal motor nucleus (DMN) –> motor to smooth muscle
function of fundus of stomach
storage function - has receptive relaxation (NO)
body of stomach
acid-pepsin secretion
where pacemaker region is located (3 contractions/min)
–> strength of contraction determined by stretch-induced release of Ach from vagus nerve and release of gastrin from antral G cells from distension, elevated pH
antrum of stomach
gastrin secretion (G cells in response to distension and elevated pH)
pylorus of stomach
controls gastric emptying into duodenum
gastric pacemaker
specialized muscle in the upper body of the stomach
cells of cajal
spontaneously depolarize and repolarize
when depolarized enough to elicit an AP (from Ach and gastrin) –> contraction
why is it important to only let small amounts of chyme into duodenum at a time?
- sample the contents
- accelerate the process of digestion by mixing contents with digestive enzymes secreted by the pancreas and bile salts delivered to duodenum from gallbladder
- begin absorption of nutrients and water from luminal contents
duodenal sampling
designed to reduce the rate of gastric emptying whenever the material in chyme suboptimal for digestion and absorption
pH of duodenal sample
if too low…stimulates secretion of secretin from duodenal cells
which (+) release of pancreatic basic juices and biliary juices for acid neutralization while also reducing gastic contractility
osmolality of duodenal sampling
if too hyperosmolar –> stimulate vagus nerve (vasovagal) reflex that reduces vagal release of Ach in the vicinity of gastric musculature for reduction in gastric contractility
fat content of duodenal sampling
if too fatty
stimulate CCK release from duodenal epithelial cells for contraction of the gallbladder and release of pancreatic enzymes
lipases
that enhance fat absoprtion while also reuding gatric contracting
general conditions that reduce gastric contraction
low pH, hyperosmolality, high fat in duodenum content
