GI Hormones Flashcards
What sort of hormone is gastrin
Polypeptide
What are the 3 biologically active forms of gastrin
What do all active forms have
- Big = 34 AAs
- Little = 17 AAs
- Mini = 14 AAs
Samr c-terminal 5 chain AA
Where is gastrin released
Where is it also present
From G cells in stomach and duodenum
CNS e.g. pituitary gland, hypothalamus
How is the release of gastrin stimulated
- Protein digestion products
- Nervous, physical distention
- Calcium
- Coffee
- WIne
How is the release of gastrin inhibited
Acidification of antrum - pH of < 2
Somatostatin
Action of gastrin
- Stimulates acid secretion by gastric mucosa
- Stimulates growth of parietal cells of gastric mucosa
- Stimulate mucosal blood flow
- Stimulates pepsin release
GASTRINOMA - ZOLLINGER-ELLISON SYNDROME
What is it caused by
What are the symptoms
- Gastrin secreting tumor
- non-beta cell tumor of pancreas (80%)
- G cell tumors in duodenum (10-15%)
- continually secretes gastrin into blood
- Symptoms
- Duodenal ulcers
- diarrhea
- steatorrhea
- hypokalemia
- increased parietal cell mass
- constant stimulation of hyperplastic mucosa
What sort of hormone is cholecystokinin
Polypeptide, different forms including: 58, 39, 33 and 8 AA
8 AA form has full biological potency
What is cholecystokinin secreted by
I cells, mainly in duodenum and jejunum distal
What is secretion of cholecystokinin stimulated by
FAs or AAs in duodenum
+ve feedback between CCK secretion and its stimulation
What is secretion of cholecystokinin inhibited by
Somatostatin
Physiological effects of CCK on gallbladder
- Emptying of gallbladder - contracts gallbladder, relaxes sphincter of Oddi
Physiological effects of CCK on pancreatic exocrine function
Potent stimulator of enzyme secretion
Physiological effects of CCK on stomach
Inhibits gastric emptying
Trophic effects of CCK
Exocrine pancreas and gallbladder mucosa
What does CCK induce
Satiety => no hunger
Why fatty food fills us up
SEE PHOTO
What sort of hormone is secretin
29 AA peptide released from S-cells of duodenal mucosa
Stimuli for release of secretin
- Acid in duodenum (pH < 4.5)
- FAs in duodenum
Physiological effects of secretin
NATURE’S ANTACID
- Inhibits gastric acid secretion
- Stimulates pancreatic and bile bicarbonate secretion
- Stimulates pepsin secretion
- Trophic effect on exocrine pancrease
- May have a role in control of food intake
What sort of hormone is Gastric Inhibitory Peptide (GIP)
Member of secretin family
- 9 AA identical to secretin
What is the stimuli for release of GIP
- Released from duodenum and proximal jejunum
- All major foodstuffs
Physiological effects of GIP
- Stimulates insulin release - also called glucose-dependent insulinotrophic peptide
- Inhibits gastric acid secretion
What sort of hormone is motilin
22 AA peptide
What are the stimuli for release of motilin
- Released from duodenum and proximal jejunum during fasting at 100 min intervals
Physiological effects of motilin
- Stimulates upper GI motility
- Accounts for migrating motility complex - housekeeping contractions
Chemical structure of somatostatin
14 and 28 AA forms
Where is somatostatin found
In hypothalamus, throughout CNS and gut, including pancreas
Function of somatostatin
Major inhibitory peptide of gut
Inhibits secretion of:
- Insulin
- Glucagon
- CCK
- Secretin
- Gastrin
- VIP
- Somatostatin - autocrine
Where is Glucagon Like Peptide 1 produced
Digestive tract
What does GLP-1 give the feeling of
Feeling full - satiety
What does GLP-1 inhibit
Gastric emptying
Glucose absorption from the gut
What does GLP-1 increase
Insulin secretion
Pancreatic Beta-cell mass
