gut motility Flashcards
what does digestion and absorption depend on
motility
chewing
mouth and salivary glands
swallowing and persitalsis
pharynx and esophagus
gastric mixing and gastric emptying
stomach
segmentation; migrating motility complex
small intestine
haustral contractions; mass movements
large intestine
how is digestion regulated
4 ways-
autonomous smooth muscle function (slow waves)
intrinsic nerve plexus
extrinsic nerve innernation
gastrointestinal hormones
rate of propulsion
different in various regions
food rapidly transits down the esophagus but is moved very slowly through the small intestine
mucosa
muscularis smooth muscle contracts it
- longitudinal muscle fibres run parallel to the tracts long axis
-circular muscle fibres run around the tracts circumference
smooth muscle stimulation results in what
contraction of the alimentary canal which propels the food forward in constant motion
what is GI motility impacted by
eletrical stimulation of muscularis smooth muscle by myentric plexus as well as extrinsic nerve innervation and gastrointestinal hormones
what is the myentric plexus a part of
the enteric nervous system
slow waves
slow spontaneous rhythmic changes in resting membrane potential of inner circular smooth muscle
what do slow waves conduct to
circular smooth muscle cells and cause phasic contractions
what slow waves cause muscle contraction
slow waves with action potential
BER
basic electrical rhythm
what are BER
constant regularly spaced circular muscle slow waves
frequency of slow waves
varies from region to region along the length of the tract
neural activity and hormonal signals can affect slow wave amplitude and trigger action potentials
digestion in the mouth
teeth and tongue begin mechanical digestion and salivary glands begin chemical digestion
function of lips and cheeks
confine food between teeth and allow for even chewing during mastication
function of salivary glands
secerete saliva so moisten and lubricate mouth and pharynx
moisten and soften and dissolve food
clean the mouth and teeth
salivary amylase breaks down starch
function of the tongue muscles
move tongue sideways and in an out to manipulate food for chewing and shape food into bolus and manipulate food for swallowing
functino of taste buds
sense food in mouth and sense taste
nerve impulses from taste buds are conducted to salivary nuclei in the brain stem and then to salivary glands stimulating saliva secretion
lingual glands
secrete lingual lipase
this is activated in the stomach
break down triglycerides into fatty acids and diglycerides
function of teeth
shred and crush food
break down solid food into smaller particles for deglutition
the pharynx
short tube of skeletal muscle lined with mucous membrane
nasopharynx
involved only in breathing and speeech
what is used for breathing and digestion
oropharynx and laryngopharynx
esophagus
thin walled and pliant muscular tube which conducts food from pharynx to the stomach
what kind of muscle is in the esophagus
both skeletal and smooth
skeletal in the upper third and smooth in the lower two thirds
what spinchter is the gastroesophageal sphincter
the cardiac or the lower esophogeal sphincter
steps of the swallowing reflex
- voluntary/ buccal phase
- pharyngeal phase
- esophageal phase
voluntary phase of swallowing
chewing transforms food into a bolus and the tongue propels the bolus into the pharynx
mechanoreceptors initiate the swallowing reflex- a series of contractions coordinated by the swallowing centre in the medulla
what happens in the orthopharangeal phase of swallowing
bolus presses downward on the epiglottis covering the glottis and preventing bolus from entering the larynx and the trachea
uvula elevates and lodges against the back of the throat sealing off the nasal passages
reflex mechanisms supress breathing motions
upper esophogeal sphincter relaxes allowing bolus entry into the esophogus
what happens in the esophogeal phase of swallowing
entry of bolus into esophagus stimulates stretch receptors triggering persitalsis
the persitalic wave propels the bolus towards the stomach
persitalsis
a series of wave like muscle contractions that propel the food bolys/chyme along the digestive tract
what causes persitalsis
coordinated activity between the circular and longitudinal muscle layers in adjoining segments of the GI tract
primary peristalsis
swallowing induced persitalsis
what happens if the bolus gets stuck
stretch receptors cause secondary persitalsis which forces the bolus down the esophagus and into the stomach
what is heartburn
when the lower esophageal sphincter does not remain closed and the contents of the stomach are expelled up the esophagus (regurtiation)
repeated over time the mucosa and submucosa of the esophagus may erode causing pain and impaired swalllowing
where does most chemical digestion begin
in the stomach
what happns to food in the stomach
smooth muscle contractions pulverize food into smaller particles and mixes it with gastric juices forming chyme
fundus
wall in the stomach and is thin and easily expands
rugae
in the body of the stomach and flatter as the stomach expands
antrum
thickest muscle layer and produces strong contractions responsible for gastric mixing and emptying
main function of the stomach
to store ingested food until it can be emptied into the small intestine at an approperiate rate
vagovagal reflex
receptive relaxation
what is receptive relaxation
stomach relaxes in response to swallowing
sensory info about entry of food is transmited to brain via vagus nerve
gastric mixing
contractile activity of stomach smooth muscle pulverizes food into smaller particles and mixes it with gastric juice forming chyme
gastric emptying
contractions of the antrum propel chyme from stomach into small intestine
rhythmic mixing waves force small amounds of chyme through the pyloric sphincter and into the duodenum
when are the contents of the stomach completely emptied into duodenum
within 2-4 hours after eating a meal
mixing wave
unique type of peristalsis that mixes and softens food with gastric juices to create chyme
they become more and more intense as they reach the pylorus
vomiting reflex
coordinated by a region in the medulla called vomiting centre
abdominal muscles contract strongly causing abdominal wall to move inward as deep inspirations move diaphragm downward which riases abdominal pressure and squeeezes the stomach
lower esophageal sphincter relaxes allowing stomach contents to enter the esophagus
strong abdominal contractions push the material through the upper esophogeal sphincter and out through the mouth
purpose of segmentation
mixes the chyme in the small intestine and slowly propels it forward
what do mimixing moveemnts do
promote digestions by mixing food with digestive juieces
facilitate absorption by exposure to surfaces of the digestive tract
what happnes during intestinal phase control
intestine distention triggers contractions that propel the intestine contents onward
what happens during gastric phase control
hormone gastrin stimulates motility in the ileum and promotes relaxation of the ileocecal sphincter to increase the rate at whcih these contents move into large intestine
what happens when the somach is empty
persitaltic migrating motility complexes sweep the intestine clean of its contents
what triggers migrating motility complexes
the hormone motilin which targets gastric and instestinal smooth muscle
what inhibits motilin
eating food
what are the specialized reflexes in the small intestine
instesine instestinal reflex
ileogastric reflex
gastroileal reflex
intestine intestinal reflex
severe distention or injury to any portion of the small intestine inhibits contractile activity thorughout the rest of the intestine
this protects the injured part from further stretching and additional injury
ileogastric reflex
distention of the ileum cuases inhibition of gastric motility which decreases the rate at which chyme enters the duodenum
gastroileal reflex
presence of chyme in the stomach triggers increased motility in the ileum
haustration
very slow segmentaion where segments (haustra) are delineated by permament folds in the intestinal wall
haustration speed
significantly slower than segmentation- about 2 contractions per hour
mass movements
3-4x per day
GMC- giant migrating contractioons of the colon
like a persitaltic wave except that a portin of the intestine contrcats for a longer time before relaxing
propel the luminal contents forward rapidly and sweep the colon clean
colonocolonic reflex
distention of one part of the colon induces relazatino of the other parts
gastrocolonic reflex
presence of a meal in the stomach triggers an increase in colonic motility and an increase in the frequency of mass movements
what triggers the defacatino reflex
distention of the rectum from the colon which initiates
1, SM contraction in wall of rectum. further inc in pressure by persitaltic contrcations of the sigmoid colon that propel fecal matter into rectum
2, interal anal sphincter relaxes while the external anal sphincter contracts preventing material from exiting the body
3, external anal sphincter relaxes allowing defacation to proceed when pressure in rectum reaches a certain level
