Physiology: Gastric Motility & Secretion Flashcards
Approx. how much gastric juice secreted from gastric glands a day?
2 L
What is the difference between the mechanical activity of the orad and caudad stomach?
-orad: tonic -caudad: phasic
What makes up the orad stomach and what makes up the caudad stomach?
-orad: fundus + proximal body -caudad: distal body + antrum
What causes the orad region to relax and what opens simultaneously?
-driven by vagus nerve during a swallow -opens simultaneously with the lower oesophageal sphincter
What causes the tonic contractions of the orad stomach to be weak and why are they weak?
- Due to relatively thin musculature
- to allow time for salivary amylase to digest starch
What hormone decreases these contractions and thus rate of stomach emtpying?
gastrin
Of the orad and caudad region of the stomach, which occurs by slow wave activity?
Caudad
How does the caudad region contract?
-When slow waves reach threshold peristaltic contraction begins in midstomach towards gastroduodenal junction
What is the antral wave/pump?
The slow wave of contraction from the mid-stomach to the gastroduodenal junction
What is retropulsion and how does it occur?
-Retropulsion is the is the rebounding of the chyme against the constricted distal antrum back into the body of the stomach -occurs by an increase in velocity of the peristaltic contraction towards the gastroduodenal junction thus overtaking the chyme
What is the function of retropulsion?
To further mix and reduce the chyme to smaller particles
What 2 gastric factors control the strength of the antral wave and thus the control of stomach emptying?
-rate of emptying proportional to volume of chyme (distension increase motility) -consistency of chyme (thinner chyme empties faster)
Through what mechanism does distension of the stomach increase motility?
stretch of smooth muscle stimulates the intrinsic nerve plexuses thus increasing vagus nerve activity and gastrin release
What 2 duodenal factors control the strength of the antral wave and thus the control of stomach emptying and why?
-neuronal response -hormonal response -duodenum must be ready to receive chyme
What is the enterogastric reflex?
It is the feedback mechanism where stretching of the duodenum leads to decrease in gastric motility in order to control the rate of chyme entering the duodenum
What is the enterogastric reflex?
It is the neuronal feedback mechanism where stretching of the duodenum leads to decrease in gastric motility in order to control the rate of chyme entering the duodenum
What are 4 stimuli drive the neuronal and hormonal responses and how do they work?
-fat (need time to digest) -acid (need time to neutralise) -hypertonicity (too much sugars can lead to osmosis and too much water coming from blood into small intestines) -distension
What is the stomach divided into in terms of secretory activity?
-oxyntic gland area -pyloric gland area
Fill in the blanks.
Label this diagram.
What cell signalling pathways do acetylcholine, gastrin, histamine, somatostatin and prostaglandins work on respectively?
- acetylcholine: PLC-IP3 pathway
- gastrin: PLC-IP3 pathway
- histamine: cAMP-PKA pathway
- somatostatin: cAMP-PKA pathway
- prostaglandins: cAMP-PKA pathway
What effect do secretagogues (gastrin, histamine + ACh) have on the K+/H+ ATPase (proton pump) in the parietal cell?
They cause the proton pumps to move from the cytoplasmic tubulovesicles to the apical membranes which extend into microvilli
What drives the cephalic phase and describe these events?
- Driven by the CNS + then vagus nerve
- activated senses of food and chewing trigger vagus nerve which acts through enteric neurones on ECL cells, G cells and release of ACh to act on parietal cells (increase HCl) and inhibits D cells to inihibit somatostatin release
