Intro to Physiology Flashcards
Name the extrinsic nervous system of the GI tract. Where are the cell bodies?
ANS
- Parasympathetic and sympathetic
Cell bodies are located outside the gut wall
Name the Intrinsic nervous system of the GI tract. Where are the cell bodies?
ENS
- Myenteric and submucosal plexuses
Cell bodies are located inside the gut wall
Describe parasympathetic innervation of the GI tract. Include the nerves, cell body location, neurotransmitters, and what it synapses with once in the gut wall
Via the vagus and pelvic nerves
Preganglionic nerve cell bodies in brainstem or sacral spinal cord
Postganglionic neurons lie in the wall of the organ
Nicotinic - ACh
Synapses with the myenteric plexus between the muscularis externa and submucosal plexus
Describe sympathetic innervation of the GI tract. Include the nerves, cell body location, neurotransmitters, and what it synapses with once in the gut wall
Via thoracolumbar region
Preganlionic efferent fibers arise within the spinal cord and end in prevertebral ganglia
Postganglionic fibers from prevertebral ganglia
Innervates myenteric and submucosal plexuses and direct innervation of the muscles
Pre-ACh Post - NE
With the vago-vagal reflux, how much of it is afferent vs efferent?
75% afferent
25% efferent
What is the sensory ganglion of the vagal nerve called?
nodose ganglion
Where are the centers that control food intake located?
within the hypothalamus
Describe paracrine signaling in the GI tract
Paracrines act locally
Signals reach target cells by diffusion over short distances
Released by enteroendocrine cells or other sensing cells
Ex. somatostatin and histamine
What is the main actions, site of release and stimuli for release of somatostatin?
Main actions: inhibits gastric H secretion directly through parietal cells or inhibit histamine or gastrin
Secreted by D cells inside the GI tract or hypothalamus and delta cells of exocrine pancreas
LOW luminal pH is the stimulus
What is the main actions, site of release and stimuli for release of histamine?
an amine that stimulates acid production through parietal cells (opposite of somatostatin)
Secreted by enterochromaffin-like cells in gastric glands
Stimuli - Gastrin (wikipedia)
Describe endocrine regulation in the GI tract
ECCs contain secretary granules filled with hormone peptides
Hormones are secreted into portal circulation and reach systemic circulation
Bind to specific receptors on target cells
Stimuli must not come from a nerve or AP, instead from a stimuli like mechanical stretch
What stimulates gastrin secretion? What is the site of secretion?
Small peptides and a.a, distention of the stomach, vagal stimulation via GRP
Site: G cells of the stomach
What are the main actions of gastrin?
Increase gastric acid secretion and stimulates growth of gastric mucosa
What is zollinger-ellison syndrome?
gastrin-secreting tumors causing an increase of circulating levels of gastrin, increase of acid secretion by parietal cells and the # of parietal cells.
Hypertrophy of gastric mucosa
duodenal ulcers
steatorrhea
what is steatorrhea?
pancreatic enzymes are impaired thus, there is an excretion of abnormal quantities of fat with the feces
What stimulates CCK secretion? What is the site of secretion?
Small peptides and a.a. and fatty acids (not including triglycerides)
Site: I cells of the duodenum and jejunum
What are the main actions of CCK?
increase pancreatic enzyme secretion, and bicarb secretion (indirectly through secretin)
Stimulates contraction of gallbladder and relaxation of sphincter of oddi
Stimulates growth of exocrine pancreas and gallbladder (trophic effect)
Inhibits gastric emptying to process fats longer
can act as paracrine signal
Increase gastric distention
Elicits satiety (acts on vagal->NTS->hypothalamus circuit to decrease release of ghrelin)
What are the receptors for CCK?
CCK1(A) - specific for CCK
CCKB - sensitivity for both gastrin and CCK
What stimulates secretin and what is the site of secretion?
H+ in the duodenum and fatty acids in the duodenum
S cells of the duodenum secrete secretin
What are the main actions of Secretin?
increase pancreatic bicarb secretion increase biliary bicarb secretion Decrease gastric H+ secretion Inhibits trophic effect of gastrin on gastric mucosa Can act as paracrine signal
What stimulates the secretion of GIP and what is the site of secretion?
Fatty acids, a.a., and oral glucose
What are the main actions of GIP?
increases insulin secretion from pancreatic beta cells
decrease gastric H+ secretion
What would be more effective in increasing insulin secretion, oral glucose administration or intravenous glucose administration?
oral glucose stimulates GIP, which stimulates insulin secretion, and also has direct stimulatory effects on beta cells
What is motilin?
Hormone that is secreted by upper duodenum
Increases motility and is released every 90 min
What is pancreatic polypeptide?
In response to carbs, proteins or lipids, it is released from pancreas and inhibits bicarb secretions
What is enteroglucagon?
in response to low blood glucose, it is released from intestines to increase glycogenolysis and gluconeogenesis
What is GLP 1?
glucagon-like peptide that is from L cells of small intestine
Increases insulin secretion from beta cells
inhibits glucagon, appetite, and gastric emptying
Describe neural regulation in the GI tract
Neurotransmitters
AP are needed for neurotransmitter release from nerve terminals in GI tract
Diffuse across synapse
What are the actions of ACh in GI tract?
contraction of Sm m.
relaxation of sphincters
Increase of salivary, gastric, and pancreatic secretion
(cholinergic)
What are the actions of NE?
Relaxation of Sm m.
Contraction of sphincters
Increase of salivary secretion
(adrenergic)
What are the actions of VIP?
Relaxation of the Sm m.
Increase intestinal secretion
Increase pancreatic secretion
(source - neurons of the mucosa and sm m)
What are the actions of GRP?
gastrin-releasing peptide causes increase of gastrin secretion
(source-neurons from gastric mucosa)
What are the actions of enkephalins?
contraction of sm m.
Decrease of intestinal secretion
(source - neurons of the mucosa and sm m. )
What are the actions of neuropeptide Y
Relaxation of sm m.
decrease intestinal secretion
(source - neurons of the mucosa and sm m)
What are the actions of substance P
Contraction of sm m.
increase salivary secretion
(source - co release with ACh)
Name the neuronal centers of the hypothalamus that participate in the regulation of food intake
lateral nuclei (LH) - feeding center Ventromedial nuclei (VM) - satiety center Paraventricular nuclei (PV) Dorsomedial nuclei (DM) Arcuate nuclei (Arc) - axons project onto satiety feeding centers
What are the types of signals that the hypothalamus receives?
Neural - GI tract
Chemical - nutrients in blood, GI hormones, leptin from adipose tissue
Physical - sight, smell, taste (cerebral cortex)
Where does most of the integration signaling regulating food intake and energy expenditure happen?
in the arcuate nucleus
Describe the pathway that insulin, leptin and CCK promotes in the arcuate nucleus
Promotes the alpha-melanocortin (a-MSH) pathway
a-MSH released by pro-opiomelanocortin (POMC) neurons
a-MSH binds to MCR-4 present in 2nd order neurons
Inhibits food intake and increases metabolism (Anorexigenic)
Describe the pathway that ghrelin promotes and that insulin, leptin, and CCK inhibits
The Neuropeptide Y (MPY) pathway
Hunger signals stimulate the release of NPY
NPY binds to Y1R
Neurons that release NPY also release agouti-related peptide (AGRP)
Increase feeding behavior and storage of calories (orexigenic)
What is an antagonist of MCR-4?
AGRP
What peptides that stimulate the a-MSH pathway also inhibit the NPY system?
Insulin, leptin, CCK
Some cases of obesity have been related to mutations in the ____ and _____ genes
POMC and MCR-4
What is Ghrelin mainly secreted by?
endocrine cells in the stomach
Ghrelin binds to growth hormone _________ receptors
Secretagogue
What does ghrelin stimulate in the hpothalamus?
neurons that release NPY
Appears to initiate the feeding response
What are the main actions of ghrelin?
increase appetite, gastric motility, gastric acid secretion, adipogenesis, insulin secretion(?)
What hormone is transported across blood brain barrier and binds to receptors in satiety and hunger centers within the hypothalamus?
insulin
What are the main actions of insulin?
decrease appetite and increase metabolism
In patients with type I diabetes mellitus there is an ____ in food intake associated with _____ insulin
increase
decrease
What are the actions of peptide YY (PYY)?
Binds to Y2 receptors of the hypothalamus after release from EECs (L cells) of the ileum and colon
Inhibits NPY neurons
Releases inhibition of POMC neurons
What is leptin secreted by?
cells in adipose tissue and endocrine cells in the stomach
What does leptin bind to?
receptors in satiety and hunger centers w/i the hypothalamus (POMC and NPY systems)
Inhibits NPY, stimulates POMC
What are the main actions of leptin?
appetite-suppressing hormone
decreases appetite, increases metabolism and decreases ghrelin release
Which muscle layer of the muscularis externa is more densely innervated and thicker?
Circular muscle layer
