General principles of GI Function remake

What does the tonic contraction of skeletal muscle

ACh via N-AChR

What relaxes the skeletal muscle?

Removal of ACh

Examples of skeletal muscle in the GI tract

UES and the external anal sphincter

What neurotransmitter is related to the smooth muscle sphincter

NE via a1

What relaxes the smooth muscle sphincter?

using NO and VIP

Examples of smooth muscle in GI tract

LES, Pylorus, Oddi, Ileocecal, internal anal sphincter

What does contraction of non-sphincter muscles?

ACh

What relaxes smooth muscle non-sphincter

NO, VIP

What does direct smooth muscle relaxation of smooth muscle non-sphincter

NE via B2

What does presynaptic inhibition of ACh

NE via a2

What do non-sphincter muscles do?

Smooth muscle non-sphincter

What is tonic contraction

relaxation from a tight state

What is phasic contraction

Tension from a relaxed state

What are the three layers of GI control

myogenic, neural, chemical

What are ICC cells

interstitial cells of cajal

What does smooth muscle + ICC cells make

baseline electrical activity

What kind of reflex does the ENS make

local

What is neural control

Local reflexes via ENS, autonomic input alters pattern

What is chemical control

Hormones and paracrines adjust baseline pattern

What is submucosal plexus also known as

meissners

What does submucosal plexus do

secretion, absorption, and local blood flow

What is the myenteric plexus also knwon as

auerbacks plexus

What does the myenteric plexus do

Motility and sphincter function

What layers does myenteric plecus do

inner circular and outer longitudinal

What excites the enteric nervous system>

ACh, substance P

What are inhibitory ENS transmitters

ATP, NO, VIP

What does VIP increase

Secretion, which relaxes smooth muscle

What does Serotonin do?

Local reflex for signaling for motility/secretion

What does GRP do

stimulates gastrin release

What is hirschsprung’s disease

aganglionosis of the distal bowel

What does hirschsprung’s disease cause?

Failure of phasic movement

What happens to circular layer peristalsis

Contraction behind, relaxation in front

What happens to longitudinal layer, peristalsis

Relaxed behind, constricted in front.

What is segementation

mixture of food via circular movement

What happens after vagal/pelvic splanchic stimulation

Preganglionic ACh N-AChR in enteric ganglia

What gets bound for ENS output of parasymp

M3R

What occurs after M3R after parasymp

Increased motility, secretion, decreased sphincter tone

What hormones are associated with M3R parasymp

NO/VIP

What happens postganglionic after sympathetic efferents are stimulated

NE is released into ENS and GI wall

What happens after A2 is stimulated symp

Decreased ACh release

What occurs when A1 binds after symp stim

Increased sphincter tone, vasoconstriction

What happens at B2 after sympathetic sim

direct smooth muscle relaxation

Effect of Sympathetic stim

Decreased motility, secretion, increased sphincter tone, decreased splanchnic blood flow

What is a short reflex?

Any reflex that stays entirely in the gut wall

Example of enteric reflex

Peristaltic reflex

Is enteric reflex short or long

short

What is a long reflex (prevertebral)

Gut → prevertebral ganglia → gut

Is prevertebral reflex long or short

long

Function of prevertebral ganglia

Coordination of activity between different gut regions

What is an example of prevertebral reflexes

enterogastric reflex

What is the enterogastric reflex

increased acid/distention/fat in duodonum causing decreased gastric motility, gastric secretion, and gastric emptying

What is Long reflex (central)

Gut → brain stem → gut

Are central reflexes short or long

long

Function of central reflexes

coordinate GI activity with vagl control, pain, and defecation

Example of central reflexes

vasovagal reflex

How does vasovagal reflex work

increased distention stimulates vgal afferents, causing the brain stem to stimulate vagal efferents to increase gastric motility and secretion

What creates slow waves/basal electrical rhythms

ICCs

What are slow waves not the same as

contractions

What does excitation of BERs cause

spikes

What does inhibition cause

reduced spikes

What determines contraction below threshold

ICC Ca2+ cycling generates the BER: no spikes in ICC/SMC

What does excitatory contraction

ACh

What does excitatory contraction cause

depol of the ICC brings BER to threshold → spike potentials are superimposed on the BER → VGCa2+ channel open in SMC, increasing Ca entry, causing more contraction

What causes contraction inhibitory input

NE, NO, VIP

What does inhbitory unput cause contraction

hyperpolarization/increased k+ conductance keeps BER below threshold, spikes are not superimposed on the slow wave, less SMC Ca2+ entry, less contraction

Source of gastrin

G cells

What secretes G cells

antrum, duodenum, jejenum

Stimuli of gastrin

Peptides, AAs, distention, vagal GRP

Inhbitors of gastrin

low pH, somatostatin, secretin, GIP

Actions of gastrin

increases HCL, pepsinogen, mucosal growth, motility

Receptor for gastrin

CCK-B/CCK2

What is zollinger-ellison syndeome

increases a lot of gastrin

Chronic PPI use

increases gastrin not too much but abit

Atrophic gastritis

Increases gastrin to an extent

Pentagastrin

Synthetic form of gastrin

Source of CCK

I cells

Where are I cells found

duodenum, jejunum, ileum

Stimuli of CCK

Fatty acids, amino acids

Inhibitor of CCK

No major

Actions of CCK

Increase bile release, pancreatic enzyme secretion, pancreatic HCO3, decrease gastric emptying

CCK receptor

CCK-A

What does CCK decrease

hunger

What can CCK worsen

pain of cholelithasis and contraction of gallblader against blocked cystic duct

Where is secretin made

S cells

Where are S cells found

duodenum, jejunum, ileum

Secretin stimuli

fatty acids, low pH

Inhbitors of seccretin

gastrin, gastric HCL

Actions of Secretin

Increase pancreatic/biliar HCO3, increase pepsinogen secretion, increase exocrine pancreatic growth

Secretin receptor name?

Secretin receptor

What does HCO3 do

neutralizes gastric acid in duodenum

What can CF cause

diminished response to secretin

What makes GIP

K cells

Where is GIP made

duodenum, jejunum

GIP stimulation

fatty acids, amino acids, carbohydrates

Inhibitors of GIP

DPP-4

What does GIP do

increases insulin, decreases gastrin and gastric HCL

Receptor of GIP

GIP receptor

What increases insulin more? IV or oral

Oral

What can be used to treat type 2 diabetics

GIP agonist or DPP-4 inhibitors

What makes GLP1

L cells