Introduction To GI Physiology Flashcards
Synapses between pre and post ganglionic parasympathetic cells are what?
Nicotinic
What do sympathetic post ganglionic nerves innervated in the GI track?
Along with the myenteric and submucosal plexi, also directly innervated the smooth muscle and glands
Sympathetic innervation does what to sphincters?
Relaxation
Describe the path or track of the Vago-vagal reflex
Vagal Afferents –> Nodose ganglion –> Nucleus of the tractus solitarius (NTS) –> Vagal Efferent
What is the main peptide used in paracrine regulation of the GI track? Also name 1 more messenger molecule
- Somatostatin
- Histamine
Molecules released through paracrine regulation are released by what cells?
Estero endocrine cells (EECs)
Somatostatin is secreted by _____ cells of the GI ________.
D; mucosa
What is the stimuli for release of somatostatin?
Decrease in luminal pH
What are the actions of somatostatin?
- inhibit gastric H+ secretion - by Parietal cells or by inhibiting histamine or gastric which regulate parietal cells
- inhibit secretion of other GI hormones
- MAIN inhibitor
Where is somatostatin secreted outside of the GI tract?
- hypothalamus
- delta cells of exocrine pancreas
Is Histamine a peptide signaler?
NO; it’s an amine
In the stomach, Histamine is stored and secreted by __________ cells in ___________ glands.
- enterochromaffin - like (ECL)
- gastric
Histamine targets what cells?
Parietal
What is the action of histamine?
Stimulate acid production
Describe the path of an endocrine hormone secreted by the GI tract
Secretion –> portal circulation –> Liver – > systemic circulation –> Target cell
Name the stimuli for secretion of Gastrin
- small peptides and a.a.
- Distention of the stomach
- Vagal stimulation (via GRP)
Name the stimuli for secretion of cholecystokinin (CCK)
- small peptides and a.a.
- fatty acids
Name the stimuli for secretion of secretin
- H+ in the duodenum
- fatty acids in the duodenum
Name the stimuli for secretion of Glucose-dependent insulinotropic peptide (GIP)
- Fatty acids
- a.a.
- Oral Glucose
What are the actions of Gastrin
- increase gastric H+ secretion
- stimulates growth of gastric mucosa (RNA and DNA and such)
- increase # of parietal cells
Describe Zollinger-Ellison syndrome
- increase circulating levels of Gastrin
- increase acid secretion by parietal cells
- hypertrophy of gastric mucosa
- duodenal ulcers
- steatorrhea (fat in feces because reduced absorptive abilities)
Actions of CCK
- Increase pancreatic enzyme secretion
- increase pancreatic HCO3- secretion indirectly by affecting secretin
- contraction of the gallbladder and relaxation of sphincter of Oddi
- growth of exocrine pancreas and gallbladder (TROPHIC)
- inhibits gastric emptying (protein and fat need more digestion time in the stomach)
- can also act as a paracrine signal
What are the two receptors for CCK?
CCK1 or CCKa: specific for CCK
CCKb: sensitivity for both Gastrin and CCK
Actions of secretin
- increase pancreatic HCO3-
- increase biliary HCO3- secretion
- decrease Gastrin H+ secretion
- inhibits trophic effect of Gastrin on gastric mucosa
- can also act as a paracrine signal
Actions of GIP
- increase insulin secretion from pancreatic Beta cells
- decrease Gastric H+ secretion
What nucleus has the feeding center?
Lateral nucleus
What nucleus has the satiety center?
Ventromedial nucleus
What nucleus feeds information into the feeding and satiety center?
Arcuate nucleus
Where does most of the integration signaling regulating food intake and energy expenditure happen?
Arcuate nucleus
Explain the alpha-melanocortin (alpha-MSH) pathway
1) alpha-MSH released by pro-opiomelanocortin (POMC) neurons
2) binds to MCR-4 present in second order neurons
3) INHIBITS FOOD INTAKE AND INCREASES METABOLISM (ANOREXIGENIC)
Explain the neuropeptide Y (NPY) pathway
1) hunger signals stimulate the release of NPY
2) NPY binds to Y1R
3) Neurons that release NPY also release agouti-related peptide (AGRP)
4) AGRP is an antagonist of MCR-4
5) INCREASE FEEDING BEHAVIOR & STORAGE OF CALORIES (OREXIGENIC)
Mutations in the POMC and MCR-4 genes can be linked to what disorder?
Obesity
Where is Ghrelin secreted?
By endocrine cells in the stomach
What does Ghrelin do in the hypothalamus?
Stimulates neurons that release NPY
List the things that Ghrelin increases
1) appetite
2) gastric motility
3) gastric acid secretion
4) adipogenesis
Where does insulin bind in the hypothalamus
Satiety and hunger centers
What does insulin do to NPY and POMC pathways, respectively
- inhibits
- stimulates
Actions of insulin
- decrease appetite
- increase metabolism
In diabetes mellitus type 1, decrease in insulin causes what?
Increase in food intake
What is CCK released by?
I cells in the duodenum
How does CCK elicit satiety?
- Acts on Vagal->NTS->hypothalamus circuit to decrease Ghrelin
- Decrease gastric emptying which increases gastric distention
Where is PYY secreted from
EECs (L cells) of the ileum and colon following a meal
What does PYY bind to
Y2 receptors of the hypothalamus
What does PYY do in the hypothalamus
- Inhibits NPY neurons
- Releases inhibition of POMC neurons
What is a possible clinical relevance of PYY?
Potential appetite suppressor
Where is Leptin secreted?
Cells in adipose tissue and by endocrine cells in the stomach
What does Leptin do the the NPY and POMC pathways respectively
- inhibits
- stimulates
Describe the appetite suppressing actions of Leptin
- decreases appetite
- increases metabolism
- decreases Ghrelin release
Post ganglionic parasympathetics innervated what in the wall of the GI track?
Either the my enteric or sub mucosal plexus
