Block 3 - General

- release of NO yields relaxation of lower esophageal sphincter, corpus cavernosum
- release of GRP yields G cells /stomach to release gastrin
(NANC)

Hormone
Origin of secretion: primarily G-cells in antrum of stomach
Primary regulation of secretion:
Stimuli: proteins; distention; vagal post-ganglionic fibers (gastrin releasing peptide); enteric nerves
Inhibitors: low pH in stomach; somatostatin from D cells in antrum of stomach
Primary functions:
• Stomach: directly stimulates parietal cell HCl
secretion, stomach wall motility, stomach mucosal
growth

Hormone
Origin of secretion: I cells throughout small intestine
Primary regulation of secretion:
Stimuli: chyme from stomach containing fat (most
important) and proteins (secondary importance)
Primary functions:
• Stomach: inhibits gastric emptying
• Small intestine: stimulates motility
• Pancreas (exocrine): stimulates enzyme secretion;
stimulates growth
• Gallbladder: stimulates contraction; relaxes Sphincter of Oddi in duodenal wall

Hormone
Origin of secretion: S cells of the duodenum of small
intestine
Primary regulation of secretion:
Stimuli: low pH in the duodenum of the small intestine
Primary functions:
• Stomach: inhibits G cells of the stomach, which
inhibits gastrin-induced HCl secretion from parietal cells
• Pancreas (exocrine): stimulates bicarbonate
secretion; stimulates growth
• Liver: stimulates bicarbonate secretion into the biliary
system

Hormone
Origin of secretion: K cells in the duodenum and jejunum of small intestine
Primary regulation of secretion:
Stimuli: protein, fat, carbohydrate in the duodenum and jejunum of small intestine
Primary functions:
• Stomach: inhibits parietal cell HCl secretion
• Pancreas (endocrine): stimulates insulin secretion

Hormone
Origin of secretion: endocrine cells in the duodenum and jejunum of small intestine
Primary regulation of secretion:
Stimulus: neural inputs (ACh) during fasting
Primary functions:
• Stomach: stimulates motility*
• Small intestine: stimulates motilility*
* activates interdigestive migrating myoelectric complex

Horomone
Origin of secretion: primarily P/D1 cells in the stomach; some cells are also in the small intestine
Primary regulation of secretion:
Stimulus: fasting
Inhibitor: feeding
Primary functions:
• Stomach: stimulates parietal cell HCl secretion,
gastric emptying, and motility
• Brain/behavior: stimulates appetite center in
hypothalamus leading to food intake
• Pituitary: stimulates growth hormone secretion

Paracrine regulation of GI function
Origin of secretion: D cells in the antrum of the stomach (paracrine); enteric nervous system interneurons (neurocrine)
Primary regulation of secretion:
Stimulus: low pH in the stomach
Primary GI functions:
Paracrine:
• Stomach: inhibits G cells to inhibit gastrin-induced HCl secretion from parietal cells; directly inhibits parietal cell HCl
secretion; inhibits pepsinogen secretion; inhibits gastric emptying
Neurocrine:
• Small intestine: inhibits motility
• Exocrine pancreas: inhibits zymogen (inactive enzyme) secretions
• Gallbladder: inhibits contraction

Paracrine reg.
Origin of secretion: enterochromaffin-like (ECL) cells in body of stomach
Primary regulation of secretion:
Stimulus: gastrin from G cells in antrum of stomach
Primary functions:
• Stomach: directly stimulates parietal cell HCl secretion; potentiates stimulatory actions of gastrin and ACh on parietal cell HCl secretion

Neurocrine Regulation of GI Functions
Origin of secretion: Sympathetic and parasympathetic preganglionic
fibers; parasympathetic postganglionic fibers
Primary functions:
• Stimulates contraction of smooth muscle in wall of digestive tube
• Inhibits contraction of digestive sphincters resulting in relaxation of sphincters
• Stimulates salivary gland acinar cell secretion
• Stimulates parietal cell secretion of HCl in the body of stomach
• Stimulates ECL cells in the body of the stomach to secrete histamine
• Stimulates pancreatic acinar cell secretion of zymogens (inactive enzymes) and pancreatic ductal cell secretion of bicarbonate

Neurocrine Regulation of GI Functions
Origin of secretion: Sympathetic postganglionic fibers; small amount from adrenal medulla
Primary functions:
• Inhibits contraction of smooth muscle wall in intestine, resulting in wall relaxation and decreased motility
• Stimulates contraction of digestive sphincters
• Stimulates salivary gland acinar cell secretion

Neurocrine Regulation of GI Functions
Origin of secretion: Enteric nervous system interneurons; also, enterochromaffin (EC) cells distributed throughout the GI mucosa; brain
Primary functions:
• Stimulates intestinal wall motility
- Activates vagal afferents

Neurocrine Regulation of GI Functions
Origin of secretion: Enteric nervous system interneurons
Primary functions:
• Inhibits contraction of smooth muscle in wall of small intestine, resulting in relaxation of wall and decreased
motility
• Inhibits smooth muscle contraction in splanchnic blood vessels, resulting in vasodilation
• Stimulates intestinal Cl- and water secretion

Neurocrine Regulation of GI Functions

The term, opiate, is a derivative of opium that was identified as a product from poppy plants that effectively treated the watery stools of dysentery, relieved pain, and produced euphoria.
Opiates produce their effects by binding to receptors for endogenously released peptidergic neurotransmitters/neuromodulators called opioid peptides. Enkephalins, endorphins and dynorphins are three distinct families of opioid peptides.

Origin of secretion: Enteric nervous system interneurons; brain
Primary functions:
• Stimulates contraction of lower esophageal sphincter, pyloric sphincter, and ileocecal sphincter
• Inhibits peristalsis in the small intestine
• Inhibits intestinal secretion
• Contributes to contraction of Sphincter of Oddi and gallbladder

Neurocrine Regulation of GI Functions

Origin of secretion: Enteric nervous system interneurons
Primary functions:
• Lower esophageal sphincter relaxation
• Inhibits contraction of smooth muscle in wall of small intestine, resulting in relaxation of wall and decreased motility
• Inhibits smooth muscle contraction in splanchnic blood vessels, resulting in vasodilation