GI Regulatory Substances Flashcards
What are the four GI functions?
- contraction/relaxation of smooth muscle and sphincters
- secretion of enzymes, fluid, and electrolytes
- trophic effects on tissues
- secretion of other GI peptides
What substances regulate GI functions?
- GI peptides (short amino acid sequences) including hormones (proteins), neurocrines, and paracrines
What are the four GI hormones?
- gastrin
- cholecystokinin (CCK)
- secretin
- glucose dependent insulinotropic peptide (AKA gastric inhibitory peptide (GIP))
GI peptides can be hormones, paracrines, or neurocrines depending on what?
where subtance is released and the route taken to reach the target cell
What type of GI peptide is released from endocrine cells of GIT (not glands) then enters the portal circulation, liver, systemic circulation, or target cells?
Hormones
What type of GI peptide is secreted by endocrine cells of GIT and acts locally within the same tissue that secretes them?
paracrines
What is the major GI paracrine hormone?
somatostatin (major inhibitory actions)
What type of GI peptide is synthesized in neurons of GIT and released after an action potential?l
neurocrines
What are the major neurocrines?
- acetylcholine
- norepinephrine
- vasoactive intestinal polypeptide (VIP)
- gastrin releasing peptide (GRP)
- enkephalins
- neuropeptide Y
- substance P
What GI hormone functions to promote hydrogen ion secretion by gastric parietal cells, stimulate growth of gastric mucosa, and increase gastric motility?
gastrin
What are the two forms of gastrin?
- big gastrin
- little gastrin
Which form of gastrin is secreted between meals at low basal levels?
big gastrin
Which form of gastrin is secreted in response to a meal (distension of stomach, presence of amino acids and peptides)?
little gastrin
What is the local vagal reflex of gastrin?
Gastrin releasing peptide (GRP) released from vagal nerves onto G cells
How is gastrin secretion inhibited?
- low gastric pH
- somatostatin
Gastrin is secreted by what cells in stomach?
G cells
What GI hormone is secreted in response to presence of fatty acids, amino acids, and peptides?
Cholecystokinin (CKK)
Cholecystokinin (CKK) is secreted by what type of cells in the duodenal and jejunal mucosa?
I cells
What are the five actions of cholecystokinin (CKK)?
- contraction of gallbladder
- secretion of pancreatic enzymes (lipase, amylase, protease)
- secretion of bicarbonate from pancrease
- growth of exocrine pancreas and gallbladder
- inhibition of gastric emptying
What is the function of the exocrine pancreas?
makes enzymes and bicarbonate
What is the function of the endocrine pancreas?
produce insulin and hormones
When cholecystokinin increases gastric emptying time, it allows for what?
adequate time for digestion and absorption
What GI hormone is secreted in response to H ions and fatty acids present in small intestine?
Secretin
Secretin is secreted by what type of cells in the duodenum?
S cells
What is the function of secretin?
- stimulates secretion of pancreatic and biliary bicarbonate
- inhibits gastrin release from G cells in stomach
What GI hormone is secreted in response to glucose, amino acids, and fatty acids?
Gastric inhibitory peptide (GIP)
Gastric inhibitory peptide is secreted by what cells of duodenum and jejunum?
K cells
Does intravenous glucose stimulate gastric inhibitory peptide?
No, only oral glucose load
What are the functions of gastric inhibitory peptide (GIP)?
- stimulates insulin secretion
- inhibits gatric H ion secretion and gastric emptying
What type of hormones are not cisdered true GI hormone due to not meeting one or more criteria?
candidate hormones
What are the four candidate hormones?
- motilin
- pancreatic polypeptide
- enteroglucagon
- glucagon like peptide 1 (GLP 1)
Which candidate hormone is secreted by the upper duodenum during fasting?
motilin
What candidate hormone is secreted by pancreas in response to ingestion of carbs, proteins, and lipids?
Pancretic polypeptide
Which candidate hormone is secreted by intestinal cells in response to decreased blood glucose?
enteroglucagon
Which candidate hormone is secreted by L cells of small intestine in response to nutrients?
glucagon like peptide 1 (GLP 1)
What is the function of motilin?
increase GI motility by initiating “interdigestive myoelectric complexes” at 90 minute intervals to move indigestible substances and bacteria to colon
What is the function of pancreatic polypeptide?
self regulates pancreatic secretion by inhibiting pancreatic secretion of bicarbonate and enzymes
What is the function of enteroglucagon?
stimulates liver to increase glycogenolysis and increase gluconeogenesis
What is the function of GLP 1?
stimulates insulin secretion from panreatic beta cells to inhibit glucagon secretion, decrease gastric emptying, and inhibit appetite
What are the GI paracrines?
- somatostatin
- histamine
Which GI paracrine is secreted by D cells of GI mucosa in response to decreased luminal pH?
Somatostatin
What is the function of somatostatin?
inhibits secretion of other GI hormones and gastric H ion secretion
Which GI paracrine has major secretion from H ion secreting area of stomach?
histamine
What is the function of histamine?
stimulates H ion secretion by gastric parietal cells
Where is the statiety center?
located in ventromedial nucleus of hypothalamus
Where is the feeding center?
located in lateral hypothalamic area
What occurs is satiety center?
anorexigenic neurons release pro-opiomelanocortin to decrease appetite
What occurs in feeding center?
orexigenic neurons release neuropeptide Y to increase appetite
What substances can influence (stimulates) anorexigenic neurons to derease appetite?
- leptin
- insulin
- GLP-1
- Peptide YY
What substances can influence (stimulates) orexigenic neurons to increase appetite?
ghrelin
What cells secrete ghrelin?
gastric cells
Peptide YY is secreted by what type of cells/
intestinal L cells
Peptide YY has a direct affect on what?
hypothalamus
What inhibits ghrelin?
Peptide YY
GLP is synthesized and secreted by what cells?
intestinal L cells
Leptin is secreted by what cells?
fat cells
