Gastro IV Flashcards
Describe the three steps of receptive relaxation and when they occur relative to the meal arriving.
Before the meal arrives: ENS inhibitory neurons are stimulated by the parasympathetic nervous system (from deglutition center).
When the meal arrives: ENS inhibitory neurons sense distension and release NANCs (local). Then, they send sensory afferents to the deglutition center, which sends vagal efferents to activate ENS inhibitory neurons.
What part of the stomach takes part in motility?
The distal part.
What part(s) of the stomach does peristalsis take place in?
It is the main form of contractile activity in the distal stomach. There is no peristalsis in the proximal stomach.
Where does peristalsis end in the stomach?
It ends at the pyloric sphincter, which contracts.
What is the trigger for gastrointestinal peristalsis?
It results from local enteric reflexes in response to local distension.
The amplitude of gastrointestinal peristalsis is determined by […]
magnitude of stimulus plus interaction of neural and hormonal factors
The frequency, direction, and velocity of gastrointestinal peristalsis is determined by […]
electrical characteristics of smooth muscle
Describe what you would see if you were to place an electrode on the upper stomach.
You would always see a constant, resting voltage of -55 mV.
Describe what you would see if you were to place on electrode on the lower stomach.
You would see rhythmic waves of partial depolarization from -55 mV to -45 mV.
What is BER?
It is the oscillating waves of partial depolarization in the distal stomach that do not cause muscle contraction.
How often do BER waves pass? How long do they last?
They last 1-4 seconds. They occur every 20 seconds, or 3 times/minute.
How does the timing of the BER vary throughout the distal stomach?
It occurs with delay as you move distally down the stomach, along the longitudinal axis. It is synchronous circumferentially.
Stomach contraction can occur when […] occur.
Second electrical signal/ERA/spikes
Describe how “the spikes” work to cause contraction.
They always appear at the peak of BER depolarization. They allow the cells to pass their action potential threshold, as they occur when the cells are their most depolarized.
What determines the number of spikes that occur during the second electrical signal?
The magnitude of the stimulus
What determines the amplitude of a stomach contraction?
The number of spikes present on a BER.
Describe the relationship between ERA pattern and stomach contraction pattern. What is the maximum number of contractions that can occur?
1 set of spikes = 1 contraction. Since the BER rhythm is 3x per minute, the maximum number of contractions you can get is 3x/minute if they all have spikes.
Does BER occur in longitudinal muscle, circular muscle, or both?
Can occur in both
What is the origin of BER?
The interstital cells of cajal (ICC).
It is non-neuronal and not from the ENS.
Where are interstitial cells of cajal located?
They are located between the smooth muscle layers and the enteric plexi, extending in circumferential and longitudinal directions.
What are the interstitial cells of cajal and what is their function?
They are non-neuronal, non-muscular cells. They function as pacemakers for the spontaneous BER seen in the gastrointestinal tract.
What are the three functions of the interstitial cells of cajal?
Can play a role in:
a) Origin and propagation of BER
b) Communication between nerves and muscle
c) Coordinating groups of muscle cells
What is the stimulus for ERA (spikes)?
Stimuli: increased stretch of muscle and release of Ach. These will lead to depolarization of musculature, which will create these spikes.
Can ERA/spikes occur on longitudinal, circular, or both types of muscular fibers?
Both
