Regulation of GI Tract Function (Hormonal and Neuronal) Flashcards Preview

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Flashcards in Regulation of GI Tract Function (Hormonal and Neuronal) Deck (45):

Enteroendocrine cell

unicellular glands that secrete regulatory substance--can act as endocrine, paracrine, or autocrine hormone


Enterochromaffin cell

Another name for enteroendocrin ecell


Enterochromaffin-like cells (ECL): What are they, where are they located, what do they secrete?

-Special class of enterocromaffin cells
-located in body of stomach
-secrete histamine


Histamine is a ___ type of hormone that stimulates _____

paracrine and autocrine, gastric acid secretion


Stimulation of further histamine secretion by interstitial histamine in ECL cell is what type of regulation of GI tract function? Explain

Autoregulation--shows organ's ability to regulate something without needing external input. Achieved by negative or positive feedback circuit.


ECL cells express an H3 type histamine receptor on their surface--binding of histamine to these receptors amplifies gastrin-induced histamine secretion by these cells

What type of regulation is this an example of?

Hormonal regulation --autocrine


Enteroendocrine cells secrete serotonin. Serotonin increases fluid and electrolyte secretion by neighboring intestinal epithelial cells.

What type of regulation is this an example of?

Hormonal regulation --paracrine

involves a very local microenvironment

note: it is paracrine regulation but it is secreted by ENDOCRINE glands in the GI tract


True or False: Neurotransmission is a special case of paracrine regulation



Glucagon-Like Peptide 1 (GLP1) is secreted into the vasculature by L cells in the small intestine. Receptors for GLP-1 are located in the stomach.

What type of regulation is this an example of?

Hormonal regulation --endocrine

unicellular glands in mucosa can secrete hormones that reach mucosal cells in distant portions of the GI tract after having reached the general circulation


What is the bioelectric rhythm (BER)?

It is a slow wave rhythm generated by intestinal smooth muscle cells -- a rhythmic depolarization-repolarization pattern


Intestinal smooth muscle cells only respond to synaptic input from _____ when the ISm membrane potential is in the ____ phase of the slow wave pattern

myenteric motor neurons, plateau phase


True/False: ISM cells can generate a certain level of contractile state called tone, and don't need to be told to contract or relax by neuronal (hormonal) input signals.



The GI tract contains its own nervous system called ____ and consists of these two division

Enteric Nervous System (ENS)
1. Myenteric plexus
2. Submucosal plexus


Role of myenteric plexus

Regulates activity of the muscularis externa (circular and longitudinal muscle)


Role of submucosal plexus

Regulates activity of mucosal cells (secretion, absorption of nutrients, electrolytes, and water) and of blood flow to mucosa (via smooth muscle tone of vessels)


The myenteric plexus is responsible for directing the ISM to produce ___

motility patterns


What are motility patterns?

Coordinated contraction-relaxation patterns by ISM fibers



Paralysis = all smooth muscle fibers are relaxes (with exception of sphincters)


Symmetrical segmentation

Mixes luminal contents without creating net longitudinal movement


Asymmetrical segmentation

Mixes luminal contents AND slow movement



Propagated wave of contraction with concomitant relaxation of segment in front of the contracted muscle. Used to move contents longitudinally at fast pace = net movement FORWARD


What does the myenteric plexus consist of?

-sensory neurons
-interneurons (secrete various neurotransmitters)
-motor neurons


Motor neurons in the myenteric plexus are ____

cholinergic or substance P-ergic


GLP1 has multiple targets when released from small intestine. Name 3

general: inhibits activity of organs that are behind them:
1. inhibits gastric emptying and HCL secretion in stomach)
2. inhibits food intake
3. primes pancreas for good insulin secretion


The glands that release GLP1 are usually (unicellular/multicellular)



Byetta/Exenatide is a GLP1 agonist that works to treat diabetes II. How might this work?

Exenatide enhances glucose-dependent insulin secretion by the pancreatic beta cell and suppresses inappropriately elevated glucagon secretion.

aka "cranks up the pancreas to make more insulin"


These cells secrete somatostatin



Somatostatin generally (activates/inhibits). Name three important examples

1. inhibits gastrin secretion from G-cells (gastrin stimulates secretion of gastric acid/HCl) by stomach's parietal cells)
2. Inhibits secretory cell or enteric neuron
3. inhibits insulin secretion
4. inhibits growth hormone


Role of histamine in GI tract

inhibits gastrin-stimulated histamine secretion in ECL cells
and stimulates proton secretion


Endocrine regulation of GI tract function by hormones secreted by glands outside the GI tract. What must the cells have in order for the endocrine hormone to act? What is an important example of an endocrine hormone?

You need receptors!
Aldosterone --distal colon has more Aldo receptors than the renal collecting ducts! Works same way as in kidney: stimulates Na+ absorption and K+ secretion


Some secretions can be neurotransmitters, paracrine regulators, or hormones. What's an important example that Grimm loves?!

Serotonin! Sero, Sara, Sara does it all!


Give an example of how serotonin does the following:
1. hormone
2. paracrine
3. neurotransmitter

1. acts on enterocytes in GI tract to stimulate fluid and electrolyte secretion; lowers pain threshold
2. promotes bone resorption
3. stimulates motility


Peristalsis reflects the action of ___ and ____

Ach and substance P


Are slow wave cycles action potentials?

No they are NOT APS! They're just slow waves of repolarization and depolarization cycles


Where is slow wave frequency highest?

Small intestine > colon > stomach


Regarding motility, these three structures are required for optimal function of intestinal motility patterns

1. intestinal smooth muscle
2. myeneteric plexus
3. ANS

1-BER and some tone
2- motility patterns, peristaltic reflex
3-modulation of activity and initiation of long distance enteric reflexes


Another name for peristaltic reflex

Intrinsic ENS reflex


In the basic design of the ENS smooth muscle unit creating the segmentation pattern, specific activity of _____ results in activation of some ____ motor neurons and inhibition of others.

Interneurons, motor.


Two examples of excitatory motor neurons

Ach and Substance P


3 inhibitory motor neurons

VIP, ATP, and NO


Explain how ENS is regulated by extrinsic system

-both SNS and parasympathetic innervate myenteric and submucosal plexus
-most likely affecting interneurons
-regulation can simply modify patterns that are being created


Does the submucosal plexus get direct innervation by parasympathetics?

No. The preganglionic neuron directly synapses on myenteric plexus, and then interplexus neurons relate the message to submucosal plexus.


Why is sympathetic innervation of the submucosal plexus more complicated?

The preganglionic neurons synapse first on a specific prevertebral ganglia. Then the project to myneteric or submucosa. Sympathetics post ganglionic neurons can also synapse directly on blood vessels and GI tract


General visceral sensory info from GI tract reaches the CNS via the ____ and ___ nerves. Pain signals reach the spinal cord via ____

vagus and pelvic splanchnic nerves

sympathetic nerves-but they are NOT sympathetic nerves! Just pain fibers hitching a ride on same highway

NB: pain fibers are NOT GVA; they are GSA!


_____ regulation predominates in all parts of the GI tract with the exception of what?

Neuronal; GI motility is primarily regulated by the enteric nervous system