L-8 Intro to GI Flashcards
what are the layers of the gut tract wall?
outer to inner
1) serosa
2) longitudinal smooth muscle layer
3) myenteric plexus (of auerbach)
4) circular smooth muscle layer
5) meissner’s plexus (submucosal plexus)
6) submucosa
7) mucosa
describe the serosa
- outer layer of CT and simple squamous epithelium
- continuous with mesentery (pathway for blood vessels to gut tube)
- missing in some parts (i.e. esophagus) replaced w adventitia connecting to abdominal wall
describe the submucosa
- incorporates blood vessels and submucosal plexus
describe the mucosa
- forms a continuous sheet lining entire G.I. tract
- loose CT w sensory nerves, blood vessels and some glands
- includes muscularis mucosa: thin layer of smooth muscle.
what are propulsive movements?
- stimulation at any point in the gut can cause a contractile ring to occur
- contractile ring moves forward after it appears
what is the usual stimulus?
distension
how else may it occur?
due to chemical or physical irritation or strong parasympathetic signals
what does it require?
the presence of functional myenteric plexus
what direction does it go?
any direction but usually dies out when heading towards the oral end
describe mixing movements
- may be caused by peristaltic contractions themselves
- at other times local intermittent constrictive contractions occur every few centimeters in the gut wall
what are slow waves?
- complex interactions among the smooth muscle cells and the interstitial cells of Cajal
what are cells of Cajal?
smooth muscle cell electrical pacemakers
further describe slow waves
- slow, oscillating potentials inherent to the smooth muscle itself in some parts of the digestive tract and spread through gap junctions
- slow waves are not action potentials
what do slow waves set the baseline for?
for intermittent spike potentials
T/F: slow waves occur spontaneously
true
where do slow waves originate?
in interstitial cells of Cajal (pacemakers)
the intensity varies btwn:
5 and 15 mv
what about the frequency ranges?
from 3 to 12 per minute (increases fomr stomach to duodenum)
*slow waves set the max frequency of contraction of each part of the GI tract
Describe spike potentials
- action potentials
- they excite muscle contractions
- occur automatically when resting membrane potential of GI smooth muscle becomes more positive than -40 mv
what happens when the slow wave potential gets higher?
the higher the slow wave potential, the greater the frequency of the spike potential
how long does it last?
10-40 times as long as a typical action potential in a large nerve fiber (10-20 ms)
what are spike potentials responsible for?
for opening calcium-sodium channels in GI smooth muscle cells
channels open and close slowly
what are some factors that cause depolarization?
- stretching of muscle
- stimulation by acetylcholine (parasympathetic)/ lack of sympathetic stimulation
- stimulation by specific GI hormones
what are some factors that cause hyperpolarization
- norepinephrine and epinephrine (sympathetic)
what are some causes of tonic contractions
- continuous repetitive spike potentials
- hormones
- continuous entry of calcium ions
pattern of motility
- local stimulus like stretch from bolus
- opens sodium channels
- slow waves pass locally thru gap junctions
- spikes occur causing action potentials
