Lecture 4: gastrointestinal Function Flashcards
What functions do GI peptides regulate in the GI tract
Contraction and relaxation of smooth muscle wall and sphincters
Secretion of enzymes for digestion
Secretion of fluid and electrolytes
Trophic (growth) effects
Some regulate secretion of other GI peptides
GI peptides: Hormones
- What are they secreted by
- Where are the target cells, local or elsewhere?
- Examples of the peptide
Peptides released from endocrine cells of GI tract
Secreted into portal circulation and enter systemic circulation
Target cells may be in GI tract or may be located elsewhere in body
Gastrin, Cholecystokinin, Secretin, and Gastric Inhibitory Peptide
GI peptides: Pancrines
- What are they secreted by
- Where are the target cells, local or elsewhere?
- Examples of the peptide
Secreted by endocrine cells of GI tract
Act locally within same tissue that secretes them
Somatostatin and Histamine
GI peptides: Neurocrines
- What are they secreted by
- Examples of the peptide
Released by neurons of GI tract following an Action Potential
ACh, norepinephrine, Vasoactive Intestinal Peptide (VIP), Gastrin-Releasing Peptide (GRP), Neuropeptide Y, and Substance P
GI peptides: Gastrin
- What are they secreted by
- Stimuili
Inhibit/stimulate what?
Secreted by G cells in stomach in response to eating
Stimuli include proteins, distention of stomach, and vagal stimulation
Gastrin-releasing peptide (GRP) is released from vagal nerve endings onto G cells
Secretion is inhibited by low pH in stomach
Promotes H+ secretion by gastric parietal cells
Stimulates growth of gastric mucosa
GI peptides: Cholecytsokinin:
Secreted by.. in response to…
5 Actions
Cholecystokinin
Secreted by I cells of small intestine in response to fatty acids and small peptides
5 Actions:
- Contraction of gallbladder
Eject bile from gallbladder into small intestine necessary for emulsification lipids
- Secretion of pancreatic enzymes
Digest lipids, carbohydrates, and proteins - Secretion of bicarbonate (HCO3-) from pancreas
- Growth of exocrine pancreas and gallbladder
-Inhibition of gastric emptying
Ensures adequate time for digestive and absorptive
GI peptides: Secretin:
Secreted by what cells… in response to…
Purpose
Secreted by S cells of duodenum in response to H+ and fatty acids
Promotes secretion of pancreatic HCO3-
Neutralizing H+ allows for pancreatic enzymes to digest fats
Inhibits effects of gastrin on parietal cells (H+ secretion and growth)
GI peptides: Gastric Inhibitory Peptide:
Secreted by… in response to…
stimulates and inhibits..
Secreted by small intestine in response to all 3 types of nutrients
Stimulates insulin secretion by pancreas
Inhibits gastric H+ secretion
GI Pancrines: Somastatin
Secreted by.. in response to…
Inhibits..
Secreted by endocrine cells in response to decreased luminal pH
Inhibits secretion of other GI hormones
Inhibits gastric H+ secretion
GI Pancrines: Histamine
Secreted by…
Secreted in H+-secreting region of stomach
Stimulates H+ secretion by gastric parietal cells (along with gastrin and ACh)
GI Neurocrines:
Where is Ach released from
Where is Norpinephrine released from
ACh (released from cholinergic neurons)
Norepinephrine (released from adrenergic neurons)
What does gastirc muscosal cells secrete and their assosicated purpose
HCl and pepsinogen initiate protein digestion
Intrinsic factor required for absorption of vitamin B12
Mucus protects gastric mucosa from HCl
Cell types of gastric mucosa
Body of stomach contains oxyntic glands
- Parietal cells → HCl and Intrinsic Factor
- Chief cells → Pepsinogen
Antrum of stomach contains pyloric glands
- G cells → Gastrin into the circulation
- Mucous neck cells → Mucus, HCO3-, and Pepsinogen
Cell type (below), location (body or antrum of stomach) and secretion
- Parietal Cells
- Cheif Cells
- G cells
- Mucous cells
- Body, HCl and intrinsitic factor
- Body, pepsinogen
- Antrum, Gastrin
- Antrum, Mucous, pepsingon and HCO3-
How does Ach regulate HCl secretion?
Released from..
Binds to..
Drug that prevents HCl release..
Released from vagus nerve
Binds to receptors on parietal cells
Produces H+ secretion by parietal cells
Atropine blocks muscarinic receptors on parietal cells