Topic 6.1 Flashcards
What are the 2 big plexuses of GI system and their fct?
- Myenteric (Auerbach) : for motility
- Submucosal (Meissner) : for digestion
On top of Ach and NE, what are some molecules that can regulate GI? (3 examples per term)
- Non peptides : 5HT3, ATP, NO
- Peptides : VIP, substance P, opioids
What are the 2 main effects of the sympathetic system on GI?
1 - circulatory : causes contraction of vessels
2 - NE can close / contract the sphincters and limit bowel movement
What is the gastroenteric reflex?
enhanced peristalsis
What mediates the gastroenteric reflex?
Myenteric plexus and gastrin
What is the gastroileal reflex?
stimulation of peristalsis in the ileum + opening of ileocecal sphincter after a meal
What facilitates the gastroileal reflex?
Gastrin
What are the gastrocolic and duodenocolic reflexes?
Distention of the stomach / duodenum stimulates evacuation of the colon. Blunted in adults
What transmits the gastrocolic / duodenocolic reflex?
The ANS
What is the enterogastric reflex?
distention and irritation of the small intestine results in suppression of secretion and motor activity in the stomach
What mediates the enterogastric reflex?
the ENS and ANS
What is the colonocolic reflex?
Propels stool caudally by proximal muscle constriction + distal muscle distention
What mediates the colonocolic reflex?
the myenteric plexus
What are the rectocolic (defecation) reflexes?
- Intrinsic reflex mediated my myenteric plexus
- Parasympathetic defecation reflex mediated by the pelvic nerve
3 types of neurons of ENS?
- Afferent neuron
- Interneuron
- Efferent neuron
What type of stimuli can activate the ENS?
- mechanical / chemical
- local / external (smell)
What is paraneoplastic syndrome?
misproduction of regulatory molecules due to cancer / tumour (called neoplasm)
7 molecules involved in endocrine regulation
- CCK (cholescystokinin)
- Gastrin
- Secretin
- GIP (gastric inhibitory peptide)
(- Ghrelin)
(- Aldosterone)
(- Calcitriol)
What produces CCK?
The i-cells in the duodenum
What is CCK useful for? (3)
- increases pancreatic juice secretion (enzymes + bicarbonate)
- decrease gastric emptying
- contraction of gallbladder
What produces Gastrin?
G cells of stomach and small intestine
What is gastrin useful for? (2)
- Gastric acid secretion
- Growth of gastric mucosa
What is secretin useful for?
- pancreatic juice secretion based on acid content of the duodenum
What produces secretin?
S-cells
What produces GIP?
K-cells of the intestines
What are the roles of GIP?
- increase of insulin secretion
- inhibition of gastric emptying (gastric content released in intestines)
What molecules is GIP a part of?
Incretins
What produces ghrelin?
P/D1 cells of the stomach, when it’s empty to signal hunger
What is the role of aldosterone in GI?
regulation of epithelial Na, K absorption in colon
What is the role of calcitriol in GI?
enhances intake of Ca2+ from the lumen
What are the 3 paracrine molecules involved in paracrine regulation of GI?
- Serotonin
- Histamine
- Somatostatin
What releases serotonin?
enterochromaffin cells
When is serotonin released by EC cells?
when there is mechanical stretch of the GI wall
What is the role of histamine in GI?
increases gastric acid secretion
What releases histamine in GI? (2)
- ECL cells (enterochromaffin like cells)
- mast cells
What is the effect of somatostatin on GI?
- General inhibitory effect : decrease gastric acid secretion, decrease nutrient absorption
What releases somatostatin?
the D cells
