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
