Digestion 4 Flashcards
Name the sequential order of all deglutition steps.
- Pressure is generated to transport the bolus to the pharynx
- Reflexes protect the airways
- UES relaxes
- Pharyngeal constrictors contract
- Primary peristalsis wave (ENS and Vago-vagal)
- LES relaxes
- Receptive relaxation of the stomach
……7.1 Vagal impulses
……7.2 Local control
……7.3 ANS influence
Where does peristalsis occur in the stomach?
In the distal stomach, it travels from the midddle towards the sphincter
Gastrointestinal peristalsis is a propagated wave of contraction that results from a series of _______ in response to __________
Local enteric reflexes
Local distension
Amplitude of contraction in the stomach depends on:
The magnitude of the stimulus
(amount of stretch and ACh interaction of neural and hormonal factors)
The frequency, direction and velocity of gastric contraction depend on:
The electrical characteristics of smooth muscle
If an electrode was placed in the proximal and in the distal stomach, what would be detected in each areas?
Proximal: No signal bc no peristalsis
Distal: Rhythmic waves of PARTIAL depolarization that do not cause a contraction
Describe the main characteristics of a BER in the distal stomach
- Synchronous contraction of tissue at “the same level”
- Delay to form a wave
- does not cause muscle contraction
What causes contraction in the stomach?
The SPIKES: the Second Electrical Signal (SES) at the peak of BER depolarisation.
T or F
The spikes can only occur at the peak of BER depolarisation
True
What determines the number of spikes? and what does the number of spikes determine?
the magnitude of the stimulus
The amplitude of muscle contraction
(more spikes, more ACh, More contraction)
T or F
If the stomach does not need to contract, there will be no BER?
F
The BER is always present and doesn’t initiate contraction
What is the maximum frequency of muscle contraction in the stomach? why?
3/min
Spikes (SES) only happen on BER and BER has a frequency of 3/min
What generates the BER in the gastrointestinal tract?
the Intersitial cells of Cajal (ICC)
What are ICC? Where are they?
pacemaker cells, non-neuronal, non-muscular between the smooth muscles and the enteric plexus, extending circumferentially and longitudinally
T of F
Contraction in the distal stomach is the same until it reaches the pyloric sphincter.
F
The contractions get stronger because the muscle wall gets thicker
What is the resting state of the pyloric sphincter? How does the sphincter close?
It is open at rest
It causes because of the terminal section of the stomach contrating
What does the small opening of the pyloric spincter ensure?
that food is broken down before reaching the duodenum
not too much acid is in the duodenum at once
What type of flow is observed in the terminal stomach, why?
There is a retropulsive turbulent flow as the chyme that does not enter the duodenum bounces back into the stomach, which allows more mixing
How does gastric emptying of liquids work?
There has to be a pressure gradient made to have emptying. However, we want a slow and controlled emptying and so a low pressure gradient. This is why receptive relaxation is important
What happens to liquid gastric emptying if the vagus nerve to the proximal stomach is cut?
There will be a big pressure gradient because of a lack of receptive relaxation. This can cause excessive stretch and acids in the duodenum
What happens to liquid gastric emptying if the vagus nerve to the distal stomach is cut?
Nothing, just no persitalsis
What factors control the antral peristalsis?
Muscle stretch to active local ENS reflexes and Vago-vagal reflexes
(no vagus is only local peristalsis (limited)
Gastric factors (_____ and _______) will ______
Duodenal factors (_______, _______, _________ and ______) will _________
stretch and ACH
increase motility
Distention, pH < 3.5, osmolarity and chemical composition
decrease motility
