1 Flashcards
Typical cross section of the intestinal wall shows the
following layers from outer surface inward:
1.Serosa.
2.Longitudinal muscle Layer.
Muscularis propria
3. Circular muscle layer.
4. Submucosa. 5. Mucosa.
mucosal muscle lie in the deeper layers of the mucosa.
The GI tract continuously provides the body with
water, electrolytes & nutrients and this requires:
- Movement of food through the GI tract.
- Secretion of digestive juices and digestion of the
food. - Absorption of water, various electrolytes, and
digestive products. - Circulation of blood through the GI organs to
carry away the absorbed substances. - Control of all these functions by local, nervous, and
hormonal systems.
Within each bundle, the muscle fibers are
electrically connected with one another through
large numbers of …………..that allow low-
resistance movement of ions from one muscle cell
to the next.
gap junctions
The smooth muscle of the GIT is excited by almost ،،،، ……….,……electrical activity along the and this can have important effects in controlling motor activity of the GIT.
membranes of the muscle fibers.This activity has two basic types of electrical waves:
continual slow, intrinsic
- slow waves 2. spikes.
Slow waves (Basic Electrical Rhythm,
BER).
Characteristics:
These waves are not action potentials.
They are slow, undulating changes in the RMP.
Their intensity usually varies between 5 -15
millivolts.
Their frequency ranges in different parts of the
human GIT from 3-12/minute.
The rhythm of contraction of:BER
1.Body of the stomach usually is about …../minute,
2.Duodenum about …../minute,
3.Ileum …./minute.
The rhythm of contraction of:
1.Body of the stomach usually is about 3/minute,
2.Duodenum about 12/minute,
3.Ileum 8-9/minute.
Gastrointestinal Smooth Muscle Functions as a Syncytium
They are arranged in bundles of as many as
1000
parallel fibers.
Most GI contractions occur rhythmically, and this
rhythm is determined mainly by the ………………………of smooth muscle membrane
potential.
frequency of “
slow waves”
cause of Slow waves
complex interactions
among the smooth muscle cells and specialized cells
called the interstitial cells of Cajal
undergo cyclic changes
in membrane potential due to unique ion channels
that periodically open and produce inward currents
(pacemaker) that may generate slow wave activity.
The slow waves usually do not by themselves cause
muscle contraction in most parts of the GIT, except
……………………..
perhaps in the stomach.
Spike potentials
1-true action potentials.
2-automatically when RMP of the GI
smooth muscle becomes more positive than about
-40 mv
3-each time the peaks of the slow waves temporarily become more positive than - 40 mv, spike potentials appear on these peaks.
4-frequency usually ranges between 1-10
spikes/second.
5-Each GI spike lasts as long as 10-20 msec.
6- The spike potentials last 10 - 40 times as long in GI
muscle as the action potentials in large nerve fibers.
7-especially large numbers of calcium ions
to enter along with smaller numbers of sodium ions
and therefore are called “ calcium-sodium channels”.
RMP averages about -….
millivolts.
When the potential becomes less negative i.e.
…………………. of the membrane, the muscle fibers
become more excitable.
When the potential becomes more negative, which
is called ………………, the fibers become less
excitable.
56
depolarization
hyperpolarization
Factors that depolarize the membrane (make it more excitable) are:
- Stretching of the muscle. 2. Stimulation by acetylcholine. 3. Stimulation by parasympathetic nerves that
secrete acetylcholine at their endings. 4. Stimulation by several specific gastrointestinal
hormones.
Important factors that make the membrane potential more -ve (hyperpolarized) & make the muscle fibers less excitable are:
- Norepinephrine or epinephrine. 2. Stimulation of the sympathetic nerves hat secrete
norepinephrine at their postganglionic endings.
Smooth muscle contraction occurs in response to entry of
calcium ions into the muscle fiber.
