Physio - GI motility (edited) Flashcards
How are smooth muscle cells in GI tract functionally coupled?
- are connected by nexus that allow fast communiction bw cells and enables them to contract together
2 different types of contraction of GI tract
- Phasic– Short contraction (peristalsis) 2. Tonic– Can last for hours until inhibited (sphincters)
T/F. Chewing is both voluntary & reflexive.
TRUE (stretch reflex) *we dont have to continuously think about chewing when eating
3 Functions of chewing
- Break down food 2. Lubricate with saliva 3. Increase surface area for chemical digestion
When bolus contacts the back of the pharynx, ________ contract.
Superior constrictor muscles -> afferent innervation sends signal to swallowing center in medulla -> sends efferent signals via nonvagal nuclei to contract muscles of pharynx & esophagus
As food moves through pharynx, ____ is closed off by epiglottis & bolus enters the _____.
Trachea; esophagus *Peristaltic movement is initiated in esophagus
The esophagus closes once bolus has passed through to prevent _____.
Reflux of material back into esophagus *Inferior constrictor muscles
Upper esophageal sphincter pressure is greater/less than atmospheric pressure.
Greater.
Below UES through diaphragm, the pressure is greater/less than atmospheric pressure.
Less. *thorax has negative pressure
Below diaphragm, the pressure is greater/less than the atmospheric pressure.
Greater.
Primary peristalsis
Initiated by a swallow
Secondary peristalsis
Not initiated by a swallow e.g. to clear any residual obstructions not cleared by the primary peristaltic wave
Gastric Esophageal Reflux Disease (GERD)
Acid reflux from stomach into esophagus - mucosa of stomach is unaffected by acid but the esophagus is susceptible to acid damage. *heart burn
Some causes of GERD
Hiatal hernia Pregnancy Failure of secondary peristalsis
Orad area of the stomach
Few & weak contractions Primary function is storage Contains oxyntic glands
Pyloric gland area of the stomach
Very strong muscular contractions
Achalasia
Due to absence of ganglion in esophagus that contains VIP. Becomes contracted and material doesn’t move through it. Also possible in colon.
Functional areas of the stomach
Orad (oxyntic gland) and Antrum.
Where in the stomach has NO contractions?
Fundus
Reflexive relaxation
Drop in fundus pressure allows the stomach to receive food Vago-vagal reflex -> VIP release causes NO release -> relaxation of the stomach
Gastric motility contraction increases/decreases in strength and rate as it goes distally
Increases
Gastric slow wave
Sets the maximum rate of contraction rate of the stomach 3-5 contractions/min **cannot be changed
What creates the slow wave potentials in the stomach?
Interstitial cells of cajal.
Amplitude of the wave is regulated how?
neural & hormonal activity *determines the strength of the contraction
Which empties faster from stomach? Liquid or solid?
Liquid. DUH!!! Also greater the volume, the more rapid the rate of emptying.
What empties fastest? Hypotonic, isotonic, or hypertonic?
ISOTONIC Saline Hypo-hypertonic inhibit emptying
Acid stimulates/inhibits emptying.
inhibits *needs time to neutralize before entering the gut
Why does fat take longer to empty from stomach?
Not water soluble -> longer to digest Triggers CCK release -> slows down gastric emptying
Failure to empty in stomach can be caused by…
Vagotomy (no vago-vagal reflex to cause peristalsis) Obstruction (ulcer or cancer)
Symptoms of failure to empty
Fullness, loss of appetite, and nausea
Increased emptying can be caused by…
Inadequate regulation
Symptoms of increased emptying
diarrhea duodenal ulcer
Almost all significant absorption occurs where?
Small intestine -> very slow progression through small intestine
Motor patterns of small intestine
Segmentation Peristalsis
Motilin release is stopped when?
Once feeding begins -> causes migratory motor complex to halt
Intestinal contraction requires ___ on slow waves.
Spikes!!! *no contraction without spike Like the stomach, the frequency of slow waves do not change, but the frequency of the spiking can change!
There is no change in amplitude of the contractions in small intestine/stomach.
Small intestine!!! Only the frequency of spiking changes
Max frequency of contraction in S.I. is greater proximally/distally.
Proximally *decreases distally
Function of the colon
Fluid & electrolyte absorption
Colon is innervated by…
Vagus n. til 2/3 transverse colon The rest is innervated by pelvic n.
Ileocecal sphincter is the junction btw
Ileum & Cecum
If ileum is distended, what happens to the ileocecal sphincter?
Relaxes and allows material into colon from ileum
What happens to the ileocecal sphincter if colon is distended?
Ileocecal valve contracts and prevents reflux of material from colon into small intestine.
Ileocecal sphincter normally has what type of contraction? Tonic or phasic?
Tonic! Not vagal.
What is the cause of the urge to poop?
2-3 times a day, haustrations in portions of colon disappear and cause peristalsis Also Rectum contracts and internal rectosphincter relaxes
What type of movement does the colon have?
MASS MOVEMENT
If conditions are not right for defecation, what happens?
External sphincter contracts and prevents defecation. Innervation via dorsal segments (pudendal n.)
