Intro To GI Physiology-1/13/16 Flashcards
List the functional layer of the GI tract:
Mucosa (epithelium, lamina propria, muscularis mucosae)
Submucosa (meissner’s plexus)
Muscularis layer (CIrcular muscle-Auerbach’s plexus-Long.Muscle)
Serosa or adventitia
The GI tract is innervated by the:
ANS and Enteric NS
Where does the extrinsic NS have cell bodies?
Located OUTSIDE the gut wall
Where does the intrinsic NS have cell bodies?
located WITHIN the wall of the gut
Describe the PARASYMPATHETIC NS for the gut
Via Vagus and Pelvic splanchnic nerves
Preganglionic nerve cell bodies are located in the brainstem or the Sacral SC
Postganglionic neurons lies in the wall of the organ (enteric neuron in the gut wall)
Synapse between pre- and post-ganglionic cells in nAChR’s
Describe the SYMPATHETIC NS for the gut
Via nerves that run between the SC and prevertebral ganglia & between these ganglia and the organs of the gut
Preganglionic EFFERENT fibers arises within the SC and end in the prevertebral ganglia
Postganglionic fibers from the prevertebral ganglia innervates the MYENTERIC and SUBMUCOSAL plexuses and other elements of ENS
Mostly, preganglionic EFFERENT fibers release Ach, while postganglionic EFFERENT nerves release NE
What type of PARASYMPATHETIC receptor is found in the Prevertebral ganglion?
What type of SYMPATHETIC receptor is found in the Prevertebral ganglion?
nAChr
nAChr
Where do you find a prevertebral ganglion in PARASYMPATHETICS?
Where do you find a prevertebral ganglion in SYMPATHETICS?
Wall of the organ within plexuses
Outside the GI tract
What type of postganglionic receptor is in PARASYMPATHETICS?
What type of postganglionic receptor is found in SYMPATHETICS?
mAChr
Alpha-adrenergic and/or beta-adrenergic
Describe the basic pathway of the ENS integrating center
Stimuli in the wall of the gut –> sensory neuron (ENS) –> Interneuron (ENS) –> Motor neuron (ENS) –> Output response
CNS can exert influence in the pathway
This type of cellular communication is local and the signals reach their target cells by diffusion over short distances
Paracrine regulation
Paracrine mediators are released by ___ cells or other sensing cells and use peptides (i.e., somatostatin) or other messenger molecules (histamine)
Enteroendocrine
This peptide is secreted by D cells (delta) of the GI mucosa and act to DECREASE luminal pH.
Somatostatin
Somatostatin acts to inhibit ___ secretion and is secreted ___ the GI tract
Gastric H+ and secretion of other GI hormones
Outside (hypothalamus or delta cells of exocrine pancreas)
In the stomach, ____ is stored and secreted by enterochromaffin-like (ECL) cells in gastric glands.
Histamine
What is the TARGET of histamine and its ACTION?
Target=Parietal cells
Action=stimulate acid production
This type of cell communication involves hormones being secreted in the portal circulation, passing through the liver, reaching systemic circulation, and finally binding to specific receptors on target cells
Endocrine regulation
Where is the site of secretion and stimuli of secretion for GASTRIN?
Site of secretion–> G cells of stomach
Stimuli of secretion –> Small peptides and AA’s, distention of stomach, and Vagal stimulation (via GRP)
Where is the site of secretion and stimuli of secretion for CCK?
Site of secretion –> I cells of duodenum and jejunum
Stimuli of secretion –> Small peptides and AA’s, fatty acids
Where is the site of secretion and stimuli of secretion for SECRETIN?
Site of secretion –> S cells of duodenum
Stimuli of secretion –> H+ in the duodenum, fatty acids in the duodenum
Where is the site of secretion and stimuli of secretion for GIP?
Site of secretion –> Duodenum and jejunum
Stimuli of secretion –> fatty acids, AA’s, oral glucose
What are the actions of GASTRIN?
Increase gastric H+ secretion
Stimulate growth of gastric mucosa
Zollinger-Ellison syndrome is a ____ tumor
Gastrin-secreting
Results in: increased circulating levels of gastrin, increased acid secretion by parietal cells, hypertrophy of gastric mucosa, duodenal ulcers, and steatorrhea
What are the actions of CCK?
Increase pancreatic enzyme secretion
Increase pancreatic HCO3- secretion (not a direct effect, potentiates the effects of secretin)
Stimulate contraction of gallbladder and relaxation of sphincter of oddi
Stimulate growth of exocrine pancrease and gallbladder (trophic effect)
Inhibit gastric emptying
Can also act as a paracrine signal
What are the actions of secretin?
Increase pancreatic HCO3- secretion Increase biliary HCO3- secretion Decrease gastric H+ secretion Inhibits trophic effect of gastrin on gastric mucosa Can also act as a paracrine signal
What are the actions of GIP?
Increase insulin secretion from pancreatic beta cells
Decrease gastric H+ secretion
What would be more effective in increasing insulin secretion?
A-Oral glucose administration
Or
B) IV glucose administration
Oral glucose stimulates GIP, which stimulates insulin secretion, and also has direct stimulatory effects on Beta cells
List the actions of Ach
Contraction of smooth muscle
Relaxation of sphincters
Increase: Salivary secretion, Gastric secretion, Pancreatic secretion
List actions of NE
Relaxation of smooth muscle
Contraction of sphincters
Increase salivary secretion
List actions of Vasoactive Intestinal Peptide (VIP)
Relaxation of smooth muscle
Increase: intestinal secretion, pancreatic secretion
List actions of Gastrin-releasing peptide (GRP)
Increase gastrin secretion
List actions of Enkephalins
Contraction of smooth muscle
Decrease intestinal secretion
What are actions of Neuropeptide Y?
Relax smooth muscle
Decrease intestinal secretion
What are actions of Substance P?
Contract smooth muscle
Increase salivary secretion
List the neuronal centers of the hypothalamus that participate in the regulation of food intake:
Lateral nucleus Ventromedial nucleus Paraventricular nucleus Dorsomedial nucleus Arcuate nucleus
This neuronal center is the “feeding center”
This neuronal center is the “satiety center”
Lateral nucleus
Ventromedial nucleus
Most of the integration signaling regulating food intake and energy expenditure happens in the ____
Arcuate nucleus
Diagram the alpha-melanocortin pathway
Alpha-MSH released by POMC neurons –> alpha-MSH binds to MCR-4 present in 2nd-order neurons –> INHIBITS FOOD INTAKE AND INCREASES METABOLISM (ANOREXIGENIC)
Insulin, leptin, and CCK act as stimulators of POMC neurons by binding to LepR on POMC neurons
Diagram the Neuropeptide Y pathway
Hunger stimulates the release of NPY –> NPY binds to Y1r of PVN neuron –> Neurons that release NPY also release Agouti-related peptide (AGRP) –> AGRP is antagonist of MCR-4 –> INCREASE FEEDING BEHAVIOR AND STORAGE OF CALORIES (OREXIGENIC)
- Ghrelin is a stimulant of AGRP/NPY neurons
- Insulin, leptin, CCK inhibit AGRP/NPY neurons
Peptides that stimulate the alpha-MSH pathway ____ the NPY system
AGRP released from the NPY pathway is an antagonist of ___
Inhibit
MCR-4
A patient who has an inhibitory mutation of POMC and MCR-4 genes will likely be predisposed to___
Obesity
___ is secreted mainly by endocrine cells in the stomach, binds to GH secretagogue receptors, and stimulates neurons that release NPY in the hypothalamus
Ghrelin
What are the actions of ghrelin?
Increase: Appetite, gastric motility, gastric acid secretion, adipogenesis, insulin secretion
Appears to initiate the feeding response
___ binds to receptors in satiety and hunger centers within the hypothalamus (POMC and NPY systems), inhibits NPY pathway and stimulates POMC pathway
Insulin
What are actions of insulin?
Decrease appetite
Increase metabolism
What does insulin do to the NPY and POMC pathways?
Inhibits NPY, Stimulates POMC
In patients with Type 1 DM, there is an ___ in food intake associated with ___ insulin
Increase
Decreased
___ is released by I cells in the duodenum and elicits satiety
CCk
How does CCK elicity satiety (pathway)?
Acts on vagal –> NTS –> hypothalamus circuit –> DECREASES ghrelin
Decreases gastric emptying –> INCREASES gastric distention
___ is released by EECs (L cells) of the ileum and colon following a meal and has the potential as an appetite suppressor
PPY
Describe the PPY pathway
PPY released by EECS of ileum and colon after a meal –> Binds to Y2 receptors of the hypothalamus (inhibits NPY neurons, releases inhibition of POMC neurons)
___ is secreted by cells in adipose tissue and by endocrine cells in the stomach and is an appetite suppressing hormone
Leptin
Describe the leptin pathway
Leptin secreted by cells in adipose tissue and by endocrine cells in stomach –> binds to receptors in satiety & hunger centers in the hypothalamus (POMC & NPY systems –> Inhibits NPY pathway, stimulates POMC pathway
Appears to be part of - feedback system for regulation of food intake
Describe the effect of Leptin on the following:
A) appetite
B) metabolism
C) ghrelin release
A) decrease
B) increase
C) decrease
What are the main functions of the GI tract?
Digestion and absorption of nutrients
Motility
Secretions
