GI Hormones

Gastrin stimuli for secretion 3

protein,

gastric distention,

and vagal stimulation (GRP)

Gastrin inhibited by

acid

What secretes Gastrin

G cells of antrum, duodenum, jejunum

gastrin action 2

Stimulates gastric acid secretion

mucosal growth

Cholecystokinin (CCK) stimuli for secretion 3

Protein

Fat

Acid

Cholecystokinin (CCK) secreted by

I cells of duodenum, jejunum, ileum

Cholecystokinin (CCK) action 5

Stimulates:

• pancreatic enzyme secretion,

• Pancreatic bicarbonate secretion

• gallbladder contraction,

• growth of the exocrine pancreas;

Inhibits

• gastric emptying and appetite

Secretin stimuli for secretion 2

Gastric Acid Juices

& Fat

Secretin Secreted by

S cells of duodenum, jejunum, ileum

Secrin Action 5

Stimulates

• pancreatic bicarbonate secretion,

• Biliary bicarbonate secretion,

• pepsin secretion,

• growth of exocrine pancreas;

inhibits

• gastrin release and gastric acid secretion

Glucose-dependent insulinotropic peptide (GIP) stimuli for secretion 3

Protein

Fat
Carboyhydrates

Glucose-dependent insulinotropic peptide (GIP) secreted by

K cells of duodenum and jejunum

Glucose-dependent insulinotropic peptide (GIP) action 2

Stimulates insulin release;

inhibits gastric acid secretion

Motilin stimuli for secretion 3

Fat,

acid,

nervous stimulation

Motilin secreted by

M cells of duodenum and jejunum

Motlin action

Stimulates gastric and intestinal motility (migrating motor complex)

Acetylcholine (Ach) stimuli for secretion

Parasympathetic (vagal) stimulation

Acetylcholine (Ach) secreted by

Parasympathetic nerve endings in ENS

Acetylcholine (Ach) action 3

Excites GI activity:

• ↑ motility

• ↑ gastric secretion

• relaxes sphincters

Norepinephrine Stimuli for secretion

Sympathetic stimulation of the adrenal medulla

Norepinephrine secreted by

Sympathetic nerve endings

Norepinephrine action 4

Inhibits GI activity:

• ↓ motility

• ↓ secretion

• ↑ sphincter tone

• vasoconstriction

Adenosine Triphosphate (ATP) stimuli for secretion

Enteric inhibitory neuron activation

Adenosine Triphosphate (ATP) secreted by

Enteric nervous system neurons

Adenosine Triphosphate (ATP) action 2

Inhibitory:

• Smooth muscle relaxation

• inhibitory junction potentials

Serotonin (5-HT) stimuli for secretion 2

Luminal distention,

mucosal stimulation by food

Serotonin (5-HT) secreted by

Enterochromaffin cells in GI mucosa

Serotonin (5-HT) action

Excitatory: stimulates peristalsis and enteric reflexes

Dopamine stimuli for secretion

Enteric neural activity

Dopamine secreted by

Enteric neurons and mucosal cells

Dopamine action

Inhibitory: decreases acetylcholine release → ↓ motility and gastric emptying

Substance P stimuli for secretion

Enteric neural stimulation

Substance P secreted by

Enteric neurons

Substance P action 2

Excitatory:

• Contraction of GI smooth muscle

• increased motility

Vasoactive Intestinal Polypeptide (VIP) stimuli for secretion 2

Enteric neural stimulation

vagal activity

Vasoactive Intestinal Polypeptide (VIP) secreted by

Enteric neurons

Vasoactive Intestinal Polypeptide (VIP) action 4

Inhibitory:

• Smooth muscle relaxation,

• vasodilation,

• ↑ intestinal secretion,

• ↓ gastric acid secretion

Somatostatin stimuli for secretion 2

Increased acid,

inhibitory feedback

Somatostatin secreted by

D cells of stomach, intestine, pancreas

Somatostatin action 3

Inhibitory:

• ↓ gastric acid,

• ↓ pancreatic secretion,

• ↓ GI motility

Leu enkephalin stimuli for secretion

Enteric opioid neuron activation

Leu enkephalin secreted by

Enteric neurons

Leu enkephalin action 3

↑ sphincter tone,

↓ intestinal secretion,

↓ motility

Met enkephalin stimuli for secretion

Enteric opioid neuron activation

Met enkephalin secreted by

Enteric neurons

Met-enkephalin action 2

↑ sphincter tone

↓ intestinal secretion