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 “dumping syndrome”?
Rapid gastric emptying leading to incomplete digestion, nausea and abdo pain after eating
What is the stomach divided into in terms of secretory activity?
-oxyntic gland area -pyloric gland area
What 5 substances are secreted by the oxyntic mucosa?
-HCl -Pepsinogen -intrinsic factor and gastroferrin -histamine -mucous
What 3 substances are secreted by the pyloric gland area?
-gastrin -somatostatin -mucous
What cells secrete somatostatin and where is it secreted into?
-D-cells -secrete into blood
What cells secrete gastrin and where is it secreted into?
-G-cells -secrete into blood
What cells secrete HCl, intrinsic factor and gastronferrin?
Parietal cells
What cells secrete histamine into the parietal cell?
enterochromaffin-like cells
What is the function of secretion of intrinsic factor and gastronferrin by the parietal cell in the stomach?
bind vitamin B12 and iron to facilitate absorption
What is the function of histamine secretion into the parietal cell?
Stimulates HCl secretion
What is the function of somatostatin secretion?
inhibits HCl secretion
What is the function of gastrin secretion?
-stimulates HCl secretion -stimulates gastric mucosa growth
What 5 channels are involved in the secretion of HCl by the gastric parietal cell?
-K+ channel -Cl- channel -Cl-/HCO3- antiporter -Na+/K+ ATPase -H+/K+ ATPase (proton pump)
Fill in the blanks.
Label this diagram.
Which secretagogues act in the direct way when stimulating HCl release?
- Histamine
- gastrin
- acetylcholine
What is the name of the gastrin receptor on the basal side of the parietal cell and ECL cell?
CCK2 receptor
What secreatgogues stimulate HCl release from parietal cells in the indirect pathway and how does this occur?
-Acetylcholine and gastrin stimulate the Enterochromaffin-like cell to release histamine which then acts on the parietal cell
What are the two substances that inhibit the parietal cell from secreting HCl?
- somatostatin
- prostaglandins
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 are the 3 phases of gastric acid secretion, when does each occur and what is released in each phase?
- Cephalic phase: before food reaches the stomach, increase in HCl secretion
- Gastric phase: when food is in stomach, increase in HCl secretion
- Intestinal phase: after food has left stomach, secretion of
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
What drives the gastric phase of gastric acid secretion?
- distension
- amino acids and other food stimuli in the stomach
What leads to the Cephalic Phase of inhibition of gastric secretion?
- decreased vagal activity following cessation of eating and stomach emptying
- also pain,nausea and negative emotions reduce parasympathetic activity
What leads to the gastric phase of inhibition of secretion of gastric secretions?
- drop in antral pH caused by food leaving stomach leads to somatostatin release
- continuing prostaglandin (PGE2) release reduces gastrin and histamine mediated HCl secretion
