Exam 2 (Neuroendocrine + Oral Digestion) Flashcards by Melanie Walukonis

Two types of clinically relevant enteric interneurons

serotonergic
enkephalinergic

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What do serotonergic interneurons facilitate?

effector neuron action

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Serotonergic NT

serotonin

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What 2 responses occur with serotonergic interneurons?

increase peristalsis
increase net fluid secretion

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What diseases can occur involving serotonergic interneurons?

carcinoid syndrome
inflammatory diarrhea (salmonella)

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Carcinoid syndrome is a ______ tumor that secretes _____.

neuroendocrine
serotonin

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Salmonella is an inflammatory diarrheal disease that increases _____ secretion.

serotonin

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Enkephalinergic interneurons overall function

establish “segmentation” pattern

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What is the lay term equivalent to enkephalinergic neurons?

“gut endorphins”

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What 2 responses occur from Enkephalingeric neurons?

-inhibit effector neurons of alternating segments (= promote mixing contents)
-decrease secretion & increase absorption

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What are the overall 3 functions of enkephalingeric interneurons?

slow aboral transit
enable mixing
increase net fluid absorption

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What is Loperamide? What’s another name for it?

synthetic opiate (type of enkephalinergic interneuron)
imodium

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Functions of Loperamide

mimics enkephalin
anti-diarrheal

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____ NS is local while ____ is outside gut wall.

enteric
extrinsic

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Which type of innervation has the dominant tone of the alimentary tract?

PSNS

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Main function of PSNS innervation of extrinsic NS

promote digestion
coordinate enteric NS

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3 responses to PSNS activity in extrinsic NS

motility patterns (peristalsis)
net fluid secretion
vasodilation splanchnic vasculature (up blood flow to GI)

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PSNS innervation = same as ______ of Enteric NS because ENS plexis = ______ neurons of PSNS

effector neurons
postganglionic

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When does the SNS of the Extrinsic NS have dominant tone on alimentary tract?

fight or flight
or
in long reflex

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Main function of SNS innervation of Extrinsic NS

inhibit digestion
recover fluid volume

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What 3 responses occur due to the SNS of the Extrinsic NS?

decreased motility (conserve E)
increase net fluid absorption
vasoconstriction of splanchnic vasc.

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(SNS/PSNS) increases blood flow to GI tract while (SNS/PSNS) increases circulating blood volume.

PSNS
SNS

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Cholinergic innervation of striated muscle occurs what two locations?

esophagus
external anal sphincter

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PSNS is made up of what 2 neuron types?

PSNS preganglionic neurons
PSNS postganglionic neurons (interneurons + effector of enteric NS)

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SNS makes up what neuron types/pathway?

CNS --> preganglionic neurons --> external ganglia --> postganglionic neurons --> gut

If the gut wall was cut off from the CNS, what NS would be intact? Which would be lost?

enteric NS intact SNS lost

What responses would be seen if CNS cut off from gut wall?

up peristalsis up secretion up vasodilation *dominant PSNS control, no SNS*

Long reflexes are part of the ____ nervous system.

extrinsic

What is the function of long reflexes?

regulate digesta over long intestine distances

What are the two main types of long reflexes?

stimulatory inhibitory

What is one type of stimulatory long reflex? What organ is acted on?

gastrocolic (stomach --> colon)

What are the 4 types of inhibitory long reflexes? What organs are acted on?

- enterogastric (SI --> stomach) - enteroenteric (SI --> SI) - coloileal (colon --> terminal part SI) - ileogastric (ileum --> stomach)

Stimulus of Gastrocolic Reflex

full stomach (stretch)

Response of Gastrocolic Reflex

increase colon motility = move content to rectum

What neuron type is present in all long reflexes?

GVA (general visceral afferent) --> send info to CNS

Outcome of Gastrocolic Reflex (PSNS/SNS)

up PSNS down SNS to colon

Stimulatory Long Reflexes overall function

speed transmit of GI contents

Inhibitory Long Reflexes overall function

slow transit of Gi contents to avoid overfilling of a segment

Enterogastric reflex stimulus

digesta in upper SI

Enterogastric reflex response

inhibit gastric emptying (decrease GI motility)

Output of Enterogastric Reflex (PSNS/SNS)

down PSNS | up SNS

Stimulus of Enteroenteric Reflex

digesta in SI (distal)

Enteroenteric Reflex response

inhibit peristalsis of intestine (distal SI inhibits site oral to it to prevent overfilling)

Enteroenteric Reflex response (PSNS/SNS)

down PSNS up SNS @ oral site

Coloileal reflex stimulus

full colon (stretch)

Coloileal reflex response

inhibit ileal emptying (decrease motility)

Coloileal reflex Output (PSNS/SNS)

down PSNS up SNS @ ileum

Ileogastric Reflex Stimulus

full ileum (stretch)

Ileogastric reflex response

inhibit gastric emptying

Ileogastric reflex (PSNS/SNS)

down PSNS up SNS @ stomach

What are the 4 different modes of action of GI hormones?

1. endocrine 2. paracrine 3. neurocrine 4. exocrine

Which mode of action for GI hormones are hormones secreted by nerve cell --> target cell (similar to NTs)?

neurocrine

Which mode of action for GI hormones use local diffusion --> target?

paracrine

Which mode of action for GI hormones enters the bloodstream directly --> target?

endocrine

Which mode of action for GI hormones enter the lumen --> target?

exocrine

What are the 3 main hormone families (GI peptide hormones for GI function)? By what similarities are they grouped?

1. Gastrin/Cholecystokinin (CCK) 2. Secretin 3. Other Grouped by amino acid composition

What are the 2 neural stimuli for gastrin?

1. acetylcholine (vagus N) 2. GRP (gastrin-releasing peptide)

What are the 2 luminal stimuli for gastrin?

amino acids (in gastric lumen) gastric pH > 4

Location of Gastrin

antrum

Cell type that releases Gastrin

G cells

Mode of Action (Gastrin)

endocrine

Target organ for Gastrin

glandular stomach

Response to Gastrin

parietal cells: HCl secretion chief cells: pepsinogen release up GI motility

Another name for CCK

pancreozymin

Luminal stimuli for CCK

amino acids (upper SI) fats (upper SI)

CCK Location

upper SI

Cell type than releases CCK

I cells

Mode of action for CCK

endocrine

Target organs & their responses to CCK (3)

1. pancreatic acini --> secrete pancreatic proenzymes 2. gallbladder --> contracts GB 3. sphincter of oddi --> relaxation (bile release)

Secretin stimulus for release

H+ ions (upper SI)

Secretin Location

upper SI

What cell type releases Secretin?

S cells

Mode of Action for Secretin

endocrine

Target for Secretin

pancreatic duct

Response to Secretin

stimulate HCO3-rich + watery secretion (hydrolatic)

What is the name for the secretion subgroup that contains 3 different GI peptide hormones?

incretin

What 3 peptide hormones are within the incretin subgroup?

1. GLP-1 / GLP-2 (glucagon-like peptides) 2. GIP (glucose-dependent insulinotropic peptide) 3. VIP (vasoactive intestinal peptide)

GLP-1 / GLP-2 Stimuli

carbohydrates (in SI) hyperosmolar solution (SI)

Location of GLP-1/2

small intestine

Cell type that releases GLP

L cells

Mode of Action of GLP-1/2

endocrine

Targets/Responses (3) of GLP-1/2

pancreatic B cells --> up insulin secretion stomach --> inhibit GI motility intestine --> mucosal growth

Which response of GLP-1/2 is via the CNS and therefore neuroendocrine?

inhibition of GI motility in the stomach

GIP stimulus

carbohydrates (in SI)

Location of GIP

small intestine

What cell type release GIP?

K cells

Mode of Action for GIP

endocrine

Target/Response of GIP

pancreatic B cells --> up insulin secretion

What GI peptide is part of the secretin family and is a neurotransmitter similar to secretin (neurocrine)?

VIP (vasoactive intestinal peptide)

Secretin release is coupled with ____ release which stimulates what?

CCK release of pancreatic proenzymes = complimentary actions of hormones

What 4 GI peptides are in the "other" family?

1. somatostatin 2. histamine 3. motilin 4. guanylin

What is the stimulus for Somatostatin release?

H+ ions (stomach pH < 4)

Location of Somatostatin

stomach

Cell type that produces somatostatin

D cells

Mode of action for Somatostatin

paracrine

Target for Somatostatin

stomach

What two cells produce responses from Somatostatin? What is their response?

parietal cells + chief cells inhibit gastric acid & pepsin secretion

What other two responses (other than from parietal & chief cells) occur from Somatostatin?

release gastrin (at G cells) release histamine (ECL)

Overall, what is the response to Somatostatin?

stop gastric secretions

Histamine neural stimulus

acetylcholine

Histamine hormonal stimulus

gastrin

What two things release histamine?

ECL cells Histaminergic nerves

Where are enteroendrocrine cells that release histamine located?

stomach

Mode of action of Histamine

paracrine (local)

Target organ for histamine

stomach

Response to histamine

HCl secretion (up gastric acid)

Motilin neural stimulus

acetylcholine

What cell type releases motilin?

M cells

Where are enterendocrine cells that release motilin located?

upper SI

Mode of action of motilin

neurocrine (neural cells)

What 2 targets does motilin act on?

stomach + SI

Motilin response

hormonal component to phase 3 migrating motor complexes (peristaltic contractions)

Guanylin stimulus

salt ingestion

What cell type releases guanylin?

goblet cells

Where are enteroendocrine cells that release guanylin located?

large intestine

Mode of action of guanylin

exocrine (into GI lumen)

Target organ of guanylin

large intestine

Response to Guanylin

stim. intestinal secretion

Which two "other" family peptides work together to stimulate clearing of digesta?

guanylin + motilin

What disease causes secretory diarrhea by E. coli toxin binding to guanylin receptor?

colibacillosis (traveler's diarrhea)

Colibacillosis is caused by E. coli toxin binding to _____ receptor = diarrhea

guanylin

Agonist-receptor interactions are similar to what?

many drugs

Agonist properties are based on ____ and ____.

affinity efficacy

Affinity

ability of hormone to bind to receptor

Efficiacy

ability of hormone to activate receptor

Match affinity + efficacy of categories of hormone agonists: (high/low/partial/none) Full agonist Partial agonist Full antagonist

Full agonist: high affinity | high efficacy Partial agonist: high affinity | partial efficacy Full antagonist: high affinity | no efficacy

Example of two hormones that increase in concentration at different times of digestion and can act on each other's receptors.

Gastrin + CCK

Increased ____ concentration occurs when the stomach fills, and as food enters SI, the _____ concentration increases, decreasing the efficacy of _____ at its receptor ____.

gastrin CCK gastrin CCKB

What is the overall result of the varying concentrations of gastrin + CCK able to act on each other's receptors?

entry of digesta in duodenum slows outflow from stomach

Example of stimulus-response coupling

crypt fluid secretion

The response to an agonist is usually dependent on ________.

2nd messengers

2 main categories of intracellular messengers

1. cyclic nucleotides (cAMP/cGMP) 2. intracellular Ca2+ mobilization

Process of cyclic nucleotide messengers when an agonist binds

1. receptor stim. ATP/GTP 2. converted to cAMP/cGMP 3. protein kinase A/G activated = secretion of Cl- + HCO3-

How long do the effects of cyclic nucleotide messengers last?

minutes to hours

Example of cyclic nucleotide messenger

VIP neurotransmitter (stim. intestinal secretion)

Clinical relevance: ______ are the main intracellular messengers in intestinal epithelia stimulated by _______ from pathogenic bacteria.

cyclic nucleotides enterotoxins

Pathological: in excess, cyclic nucleotides cause what?

secretory diarrhea

Intracellular Ca2+ mobilization (2nd messenger) is (shorter/longer) acting than cyclic nucleotides.

shorter

Intracellular Ca2+ mobilization process when an agonist binds

Receptor increases intracell. Ca2+ (direct via protein kinase C or calmodulin = epithelial fluid secretion

How long do the effects of intracellular Ca2+ mobilizations last?

seconds to minutes

Example of intracellular Ca2+ mobilization

cholinergic neural stim. of intestinal secretions

(Cyclic nucleotide / intracellular Ca2+ mobilization) second messenger method is not used by many pathogens.

intracellular Ca2+ mobilization

Systemic hormones don't originate from ____.

GI tract

_____ hormones are systemic hormones.

adrenal

Two types of adrenal hormones (systemic)

epinephrine adrenocorticosteroids

Two sub-types of adrenocorticosteroids

aldosterone glucocorticoids

Epinephrine uses (PSNS/SNS) action via adrenergic receptors.

SNS

3 responses to epinephrine

1. down motility 2. up absorption 3. down GI blood flow

Aldosterone increases ____ absorption in the colon / salivary duct.

Na+

What 2 things increase due to aldosterone production?

1. Na+ channels (ENAC) 2. Na+ pump

Aldosterone has the same effect in _____ as in the colon/salivary duct.

distal tubule of kidney

What 3 responses occur from glucocorticoid secretion?

1. up Na/K ATPase 2. down prostaglandin tone 3. suppress immune system

Submucosal control is (systemic/local).

local (paracrine)

In a non-pathological state, prostaglandins promote what 3 things?

1. motility 2. secretion 2. vasodilation (up flow)

In a pathological state, submucosal control causes increase in _____ & ____, leading to what 2 responses?

WBCs & prostaglandins diarrhea & intestinal muscle spasms

What are the 4 cell types under submucosal control?

1. fibroblasts 2. macrophages 3. PMNs + eosinophils 4. mast cells

What cell type is the major source of prostaglandins in the physiological state under submucosal control?

fibroblasts

Fibroblasts produce prostaglandins when there is ____ damage for what purpose?

mucosal protective: up flow + secretion = flush & repair

What cell type produces just prostaglandins under submucosal control?

macrophages

What two substances do PMN's & eosinophils produce under submucosal control?

prostaglandins serotonin

What cell type is aligned with effector neurons in intestine and release histamine?

mast cells

Which cell type under submucosal control has a role in allergic states?

mast cells

Histamine release from mast cells causes what?

increased fluid secretion = "wash away" antigens

Why do food allergies occur?

up food sensitivity to food antigen = diarrhea

Term for "seizing & conveying of food into the mouth"

Prehension

Cattle prehension organ

tongue (grasp grass + scoop grain)

Sheep prehension organs

tongue + cleft upper lip *graze closer to ground*

Horse prehension organ

mobile upper lip (fine motor movements)

Pig prehension organ

pointed lower jaw (root/shovel)

How do herbivores & omnivores drink?

via suction

How to carnivore undergo prehension?

tearing movements (teeth, jaws, head)

How to carnivores drink?

lapping

4 functions of mastication

1. reduces food size 2. up surface area 3. break cellulose (more starch available) 4. mixes food w/ saliva

What 3 things does mixing food with saliva add to it for mastication?

buffers enzymes mucous

What is the first step of mastication?

biting smaller bits (reduce size) to increase surface area

Herbivores masticate by ________ to increase surface area.

grinding of plant matter

Ruminants grind plant matter during initial intake and ______.

rumination

Cheek teeth of herbivores are (hypsodont/brachydont) meaning _____.

hypsodont continuously growing

What kind of teeth have rough table surface & lateral + vertical movements of the jaw?

cheek teeth

Carnivores masticate only to ______.

reduce food to swallowing size

Omnivores masticate on _____ diet while gulping on _____ diet.

plant carnivorous

What condition do lateral + circular movements cause on horses?

"points" on outer upper arcade & inner lower arcade

What is the main sign of "points" on teeth? How is it treated?

dropping food float teeth

What tools are used to float horse teeth?

long handled rasps to grind down teeth

2 signs of malocclusion

weight loss drop food

Malocclusion occurs when maxillary arcade (overgrows/stops growing) and mandibular arcade (overgrows/stops growing).

overgrow stops growing

How do you treat malocclusion horses?

soak pelleted horse feed in water = "gruel" so they can eat