Control of GI Function

Question 0

Meissner’s Plexus

Answer 0

The Mucosal nerve plexus that sits between the submucosa and the circular muscle layer

Question 1

Layers of the Gi Tract (Towards lumen)

Answer 1

Serosa, Longitudinal Muscle, Myenteric Plexus, Circular Muscle, Submucosal Plexus, Submucosa, Muscularis Mucosae, Lamina Propria, Epithelium

Question 2

Auerbach’s Plexus

Answer 2

Also known as the myenteric plexus, auerbach’s plexus sits between longitudinal and circular muscle layers.

Question 3

How do hormones of the GI tract reach target cells? How does this differ from paracine/neurocrine mechanisms.

Answer 3

They are secreted into portal circulation, reach the liver, pass into systemic circulation and then eventually arrive at target. The paracrine and neurocrine mechanisms reach the target cells immediately.

Question 4

Effect of sympathetic nervous system on Gi tract?

Answer 4

Inhibits digestion.

Question 5

Effect of parasympathetic nervous system on GI tract?

Answer 5

Stimulates digestion via vagus, especially in esophagus and stomach.

Question 6

Voluntary CNS responses in GI system?

Answer 6

Control of swallowing, contraction of the external anal sphincter.

Question 7

How does parasympathetic input to GI tract work?

Answer 7

Vagal nerves from the medulla innervate to the distal colic flexure. Then pelvic nerves from the sacral spinal cord innervate the lower colon. First nerve releases ACh to NAChRs. Second nerve releases ACh or peptide to muscarinic receptor on gut.

Question 8

How does sympathetic innervation of the GI tract work?

Answer 8

Thoracolumbar nerves enter either the chain ganglia (for control of esophagus), or the prevertebral gangia (celiac, superior/inferior mesenteric). First nerve releases ACh, second releases NE.

Question 9

Where do the following synapses occur? 1) First parasympathetic. 2) Second sympathetic?

Answer 9

Myenteric plexus (Auerbach’s).

Question 10

Enteric Nervous System

Answer 10

Includes Myenteric (auerbach’s) plexus and the submucosal (meissner’s plexus).

Question 11

Myenteric Plexus

Answer 11

Also called Auerbach’s, Located between longitudinal and circular layers of muscle. Provide motor innervation to both layers. Provides secretomotor innervation to the mucosa.

Question 12

Submucosal Plexus

Answer 12

Also called Meissner’s. Contains cell bodies of the enteric nervous system.

Question 13

Do neurons in the ens contain one NT? Or more?

Answer 13

More than one.

Question 14

NT responsible for sphincteric relaxation

Answer 14

NO

Question 15

Enterochromaffin cells

Answer 15

GI hormone secreting cells. Found in islets and between mucosal cells. Can release histamine, dopamine, other regulatory peptides (CCK).

Question 16

What type of chemical transmitters are most abundant in the GI tract?

Answer 16

Regulatory peptides.

Question 17

Gastrin: Receptor, producing cell location, stimulation/inhibition, actions.

Answer 17

Binds to CCK receptor B. Made by G cells in the antrum and duodenum. Stimulated by high gastric pH and AAs. Inhibited by gastric acid. PROMOTES GASTRIC ACID SECRETION FROM PARIETAL CELLS. Also a growth factor for enterochromaffin like cells.

Question 18

Parietal Cell

Answer 18

Makes gastric acid in response to gastrin, histamine, ACh. Has K-ATP hydrogen pump.

Question 19

Effect of gastrin on parietal and ECL cells?

Answer 19

Agonist. ECL cells produce histimine which stimulate parietal cells.

Question 20

Cholecystokinin

Answer 20

Binds to CCK-A receptor. Made by I cells in the proximal 2/3 of small intestine in response to fatty acids and AAs. Causes gallbladder contraction, secretion of pancreatic enzymes, slows gastric emptying, induces satiety.

Question 21

Secretin

Answer 21

Made by S cells in the proximal small intestine. Stimulated by gastric acid and harsh foods/alcohol. Induces secretion of HCO3 from pancreas. Inhibits gastrin release, inhibits intestinal motility.

Question 22

VIP

Answer 22

Vasoactive Intestinal Peptide. Neuromediator from enteric nervous system. Stimulates epithelial cell secretion, causes smooth muscle relaxation (relaxes LES, Oddi).

Question 23

Glucagon

Answer 23

Made by pancreatic alpha cells and L cells of the small intestine/colon. Must be processed from proglucagon in pancreas. Regulates glucose homeostasis.

Question 24

GLP

Answer 24

Glucagon like peptide, cut from proglucagon in small intestine, GLP1 regulates glucose homeostasis and GLP2 maintains GI mucosal mass because of its growth factor activity.

Question 25

GIP

Answer 25

Glucose-Dependent Insulinotropic Polypeptide. Made by K cells, released in response to hyperglycemia; stimulates beta cells of pancreas to secrete insulin.

Question 26

Substance P

Answer 26

Neurocrine and paracrine release mechanisms. Proinflammatory, pain sensation. inhibits somatostatin and biliary secretion.

P= Proinflammatory/pain

Question 27

GRP

Answer 27

Gastrin-releasing peptide. Neurocrine, mediates the vagal release of gastrin. Stimulates GI motility and pancreatic secretion.

Question 28

Motilin

Answer 28

Made in duodenum, but binds to smooth muscle receptors on gut to cause pro-kinesis.

Question 29

How does erythromycin effect the gut?

Answer 29

It is a motilin agonist.

Question 30

Ghrelin

Answer 30

Made in the gastric fundus, increases food intake. Fed state- low levels of gastrin. Upregulated in Prader-Willi syndrome.

Question 31

PP

Answer 31

Pancreatic polypeptide. Inhibits pancreatic exocrine secretion and gut motility.

Question 32

PYY

Answer 32

Peptide YY, made in L cells in the distal small intestine (ileum). Stimulated by fatty meals. Is the ileal break, which slows small intestine mobility to increase absorption time. Don’t want to keep sending things to the small intestine if its already busy. Can be compromised in patients with ileal resections, causing diarrhea.

Question 33

NPY

Answer 33

Neurocrine Homologue of PYY, stimulates appetite and acts as an ileal break.

Question 34

Somatostatin

Answer 34

Made by D cells in the antrum. Important to know. Live close to G cells and are pH sensors. Acts as a global inhibitor to stop gastric acid secretion, pancreatic secretion, bile flow, slows motiility.