Digestive 3 Flashcards
What is the UES neural control?
Vagus nerve
Describe the UES at rest.
There is constant ACh release at rest. At rest it is closed
What happens at the UES during deglutition?
There is a cessation of impulses from the vagus nerve causing a relaxation of the sphincter
Why are there a UES and a LES?
to control pressure from the pharynx to the stomach and avoid air in the digestive tract
What are the important esophageal forces (and their importance)?
Gravity: small effects on fluids
Peristalsis: most important
Each time we swallow a ________ is generated. It’s a _______.
Primary peristalsis wave
deglutition reflex
What is the primary peristalsis wave (deglutition reflex) controlled by? (what and organisation)
Vagus somatic fibres reach the striated portion in a sequential wave (fired one after the other down the esophagus)
Vagus autonomic fibres reach the ENS in smooth muscle with a synchronous activation but an increased latency for the distal esophagus (more time stimulation/response)
What happens if the vagus nerve is cut high in the neck vs transthoracically?
Neck: There will be no primary peristalsis wave
Transthoracically: The proximal branch of the vagus nerve will be able to activate the ENS (intact) the wave will continue through the ENS without other stimulation from the vagus
What are the essential roles of each the vagus nerve and ENS in deglutition?
Vagus: essentiel for initiation in the proximal esophagus
ENS: essential for continuing and propagation through the distal esophagus
What happens if the bolus gets stuck in the esophagus (not choking, just stuck)
- Local distention
- Stretch receptors can activate enteric and long reflexes
Make a secondary peristalsis wave
Enteric: short, local reflexes
Long reflex: vagal-vagal reflex
What is the vagal-vagal reflex in the case of a second peristalsis wave?
Afferent vagus fibres reach the deglutition center and cause the autonomous fibres to make the new wave
Anatomy of the LES?
half above and half below the diaphragm
What causes the closure of the LES?
it’s a myogenic closure, it’s a property of the muscle
What causes relaxation of the LES?
local ENS releases NANC (-) OR there is a vagal stimulation to the ENS inhibitory fibers
It’s part of the deglutition reflex!!!
Why is it important to have an intrathoracic and an intraabdominal portion of the LES? When does is not happen?
To maintain pressure in the tract when abdominal pressure increases
Hernias don’t allow equalising of the pressures. (sphincter won’t close)
T or F
Gastrin helps contract the LES
Both
It will do so at very very high concentrations of gastrin. It will not have those effects in the body
Why can there be more heartburn during pregnancy?
more elevated levels of progesterone can lower the resistance of the LES. There can be more reflux and thus cause heartburn
What are the motor functions of the stomach? (3)
- temporary storage (1-2L)
- Disruption and mixing of contents
- Propulsion into duodenum
What are the important structural differences in the stomach?
Proximal half: for storage and thin-walled
Distal half: for mixing + propulsion with thick walls
What is particular about the gastric mucosa?
Consists of folds called rugae
Contains different cell types (pits and gland, originate from epithelial)
What is particular about the gastric muscularis externa?
It has an extra layer: oblique smooth muscle
How does the stomach accomodate for a meal?
It has receptive relaxation: the volume will increase and keep a similar gastric pressure
How is receptive relaxation a part of the deglutition reflex?
Vagal efferents will reach the stomach before the meal arrives to relax the proximal stomach
What happens at the moment food has reached the stomach (neural control)?
LOCAL stretch receptors will cause ENS inhibitory to be activated and relax the stomach wall to relax
What happens after the local control of receptive relaxation?
There as another vagal-vagal reflex
What happens during receptive relaxation if the vagus nerve is cut (close to the proximal stomach)?
Only the local neural control will be effective, resulting in a limited relaxation and a great increase in intragastric pressure. Food will not stay long in the stomach.
For the stomach walls to relax, what NT are released and from what?
NANC NT from the ENS inhibitory neuronsThe
The local distention of the stomach created by ______ activates the ______ and _______ reflexes which ________.
entering meal
local/ enteric
long/ vago-vagal
receptive relaxation
Where does receptive relaxation happen?
in the proximal stomach
