1 Intro To GI Phys Flashcards
Functions of the GI tract
Digestion, absorption of nutrients, motility, secretions
GI sphincters name (7) and function
UES, LES, pyloric, sphincter of Oddi, Ileocecal valve, internal and external anal sphincter
Fx: restrict passage of intestinal content and optimizes digestion and absorption
Functional layers of the GI tract
Mucosal, submucosa, muscle (circular and longitudinal), Serosa
What part of the Enteric Nervous System is in the layers of the GI tract?
What layers?
Innervated by what?
Does it need the CNS?
Submucosal plexus: submucosa
Myenteric plexus: muscle
Extrinsic autonomic nervous system
NO
Where does the ENS receive its information?
Parasympathetic and sympathetic NS and CNS
Sensory info from mechanoreceptors and chemoreceptors in the mucosa
Function of the ENS
Controls contraction, secretion, and endocrine function of the GI tract
CNS role in the regulation of the GI tract (3)
Vago-vagal reflex
Modulate ENS response
Centers that control food intake in brain
Sensory ganglion of the Vagal N
Nodose ganglion
Example of a vago-vagal reflex
Gastric receptive relaxation reflex
NTS
Nucleus of the tractus solitarius
Nerves of the parasympathetic innervation
Vagus and pelvic nerves
Location of the parasympathetic preganglionic nerve cell bodies
Brainstem or sacral spinal cord
Location of the parasympathetic postganglionic neurons
Wall of the organ (enteric neuron in the gut wall)
What type of synapse is between the parasympathetic pre and post ganglionic cells?
Nicotinic (nAChRs)
Where do the sympathetic preganglionic efferent fibers begin and end?
Begin in spinal cord (thoracic and lumbar)
End in prevertebral ganglia
Sympathetic postganglionic fibers from the prevertebral ganglia innervate _________
Myenteric and submucosal plexuses
Sympathetic preganglionic efferent fibers release______.
Sympathetic postganglionic efferent nerves release ______.
Ach
NE
Long preganglioic fibers, short postganglionic fibers
Parasympathetic NS
Short preganglionic fibers, long postganglionic fibers
Sympathetic NS
How do paracrine signals reach their target cells?
Where do they act?
Diffusion over short distances
Locally
Function of paracrine regulation
Action of peptides or other messenger molecules
Examples of paracrine signals
Somatostatin and histamine
Secreted by D cells in the GI mucosa
Somatostatin
Inhibits secretion of gastric H+ and other GI hormones
Somatostatin
Somatostatin is secreted by_______.
D cells of the GI mucosa
Hypothalamus
Delta cells of the exocrine pancreas
Stimulated by a decrease a in luminal pH
Why?
Somatostatin
Low pH signals somatostatin to inhibits gastric H+ secretion
Stored and secreted by enterochromaffin-like (ECL) cells
Histamine
Histamine is secreted in the _____.
Gastric glands of the stomach
Histamine targets and action
Parietal cells in the stomach gastric glands
Stimulates acid production
Action of histamine
Stimulates acid production
Endocrine regulation
Action of hormones
Hormones secreted into circulation
EECs
Enteroendocrine cells
Contain secretory granules filled with hormones that are released upon stimulation
Examples of endocrine regulation (4)
Gastrin, cholecystokinin, secretin, glucose-dependent insulinotropic peptide (GIP)
Gastrin site of secretion
G cells of stomach
Stimuli of gastrin (3)
Small peptides and amino acids
Distention of stomach
Vagal stimulation via GRP
Actions of gastrin (2)
Increase gastric H+ secretion
Stimulate growth of gastric mucosa
Cholecystokinin (CCK) is secreted from _____.
I cells of duodenum and jejunum
Stimuli of CCK (3)
Small peptides and amino acids
Fatty acids
Actions of CCK (7)
Increase pancreatic enzyme secretion
Increase pancreatic HCO3- secretion
Stimulate contraction of the gallbladder
Relax sphincter of Oddi
Stimulate growth of the exocrine pancreas and gallbladder
Inhibit gastric emptying
Act as a paracrine signal
T or F: the increase of pancreatic HCO3- by CCK is a direct effect
FALSE
This is a indirect effect
It potentiates the effects of secretin
T or F: when CCK stimulates the growth of the exocrine pancreas and gallbladder, it is a trophic effect.
TRUE
Secretin is secreted by ______.
S cells in the duodenum
Stimuli of secretin
H+ in the duodenum
Fatty acids in the duodenum
Actions of secretin (5)
Increase pancreatic secretion of HCO3-
Increase biliary secretion of HCO3-
Decrease gastric H+ secretion
Inhibits trophic effect of gastrin on gastric mucosa
Acts as a paracrine signal
GIP
Glucose-dependent insulinotropic peptide
GIP secreted from _______.
Duodenum and jejunum
Stimuli of GIP (3)
Fatty acids
Amino acids
Oral glucose
Actions of GIP (2)
Increase insulin secretion from pancreatic beta cells
Decrease gastric H+ secretion
What is more effective in increasing insulin secretion? And why?
A. Oral glucose
B. Intravenous glucose
A. Oral glucose stimulates GIP-> stimulates insulin secretion and has a direct stimulatory effect of beta cells of the pancreas
Neural regulation
Action of neurotransmitters
What is needed for a neurotransmitter release?
Action potential
Neurotransmitters diffuse across the ______ and bind to their _______ in the ________.
synapse
specific receptor
postsynaptic cell
Cellular communication is the key to _______.
Regulation of the GI tract
Source of ACh
Cholinergic neurons
Actions of ACh (5)
Contraction of smooth m.
Relaxation of sphincters
Increase salivary secretion
Gastric secretion
Pancreatic secretion
Source of norepinephrine
Adrenergic neurons
Actions of NE (3)
Relaxation of smooth m in wall
Contraction of sphincters
Increase salivary secretion
Source of vasoactive intestinal peptide
Neurons of the ENS
Actions of VIP (3)
Relaxation of smooth m
Increase intestinal secretion
Increase pancreatic secretion
Source of nitric oxide (NO)
Neurons of the ENS
Action of NO
Relaxation of smooth m
Source of gastrin-releasing peptide (GRP)
Vagal neurons of gastric mucosa
Action of GRP
Increase gastrin secretion
Source of enkephalins
Neurons of the ENS
Actions of enkephalins
Contraction of smooth m
Decrease intestinal secretion
Source of neuropeptide Y
Neurons of the ENS
Actions of neuropeptide Y
Relaxation of smooth m
Decrease intestinal secretion
Source of substance P
Co-release with ACh by neurons of the ENS
Actions of substance P
Contraction of smooth m
Increase salivary secretion
Incretin Effect
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