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Questions and Answers
Which neurocrine is responsible for the relaxation of gut smooth muscle?
Enkephalins decrease smooth muscle tone in the gut.
False
What peptide is associated with the release of gastrin from the gastric mucosa?
GRP (Bombesin)
The peptide __________ is found in the gut mucosa and is known to increase smooth muscle tone.
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Match the neurocrines with their respective actions:
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What stimulates the release of somatostatin?
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Somatostatin can enhance the release of gut hormones.
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Which cells in the stomach release histamine?
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Histamine H2 receptor blockers such as ______ and ______ are used to decrease acid secretion.
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Match the following substances with their respective effects:
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What is one of the primary sources of Glucose-Dependent Insulinotropic Peptide (GLIP)?
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What type of peptide is described as a linear 22 amino acid peptide and is unrelated to other hormones?
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GLIP can only be stimulated by intravenous glucose.
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What are the physiological effects of GLIP?
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The release of this peptide is solely controlled by hormonal mechanisms.
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GLIP is identical to secretin in kind and position with __________ amino acids.
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What physiological effect does the peptide have on the upper gastrointestinal tract?
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The peptide is released from M-cells of the duodenum and proximal jejunum during __________ at 100 min intervals.
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Match the following effects with their corresponding actions:
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Match the physiological effects to their descriptions:
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What is the primary physiological effect of secretin?
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Secretin is released in response to fatty acids in the duodenum.
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From which cells in the duodenum is secretin released?
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Secretin is known to stimulate ________ secretion from the pancreas.
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Match the effects of secretin with their descriptions:
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Study Notes
Neurocrines Overview
- Neurocrines are peptides involved in physiological regulation, mainly within the gastrointestinal (GI) tract.
Vasoactive Intestinal Peptide (VIP)
- Found in gut mucosa and smooth muscle (SM).
- Promotes relaxation of gut smooth muscle.
Gastrin-Releasing Peptide (GRP)
- Located in gastric mucosa.
- Stimulates gastrin release, which is crucial for gastric acid secretion.
Enkephalins
- Present in gut mucosa and smooth muscle.
- Increases smooth muscle tone, playing a role in gut motility.
Somatostatin
- Found in gastric/duodenal mucosa and the pancreas.
- Release is stimulated by acidic conditions and inhibited by acetylcholine (ACh).
- Inhibits the secretion of all gut hormones, including a direct effect on parietal cells to reduce acid secretion.
Histamine
- Released from gastric cells upon gastrin and ACh stimulation.
- Plays a key role in stimulating gastric acid secretion.
- Histamine H2 receptor antagonists, such as cimetidine and ranitidine, reduce acid secretion.
Release Stimuli and Regulation
- Various neurocrines are released from M-cells in the duodenum and proximal jejunum during fasting at intervals of approximately 100 minutes.
- Release mechanisms are primarily under neural control.
Glucose-Dependent Insulinotropic Peptide (GLIP)
- A member of the secretin family, composed of 9 amino acids identical to secretin.
- Secreted by K-cells in the duodenum and proximal jejunum.
- Stimulated by major foodstuffs, especially hydrolyzed fats and oral glucose.
- Enhances insulin release and inhibits gastric acid secretion.
Secretin
- Released from S-cells in the duodenal mucosa.
- Stimuli for its release include acidic pH (less than 4.5) and fatty acids in the duodenum.
- Known as "Nature's Antacid," it inhibits gastric acid secretion and stimulates pancreatic and bile bicarbonate secretion.
- Synthesized as a preprohormone, it is a 27-amino acid peptide with no active fragments; the entire molecule is necessary for biological activity.
Cholecystokinin (CCK)
- Released from I-cells in the duodenum and jejunum.
- Stimulated by fatty acids, monoglycerides, peptides, single amino acids, and minimal acid.
- Functions include stimulating gallbladder contraction, enzyme secretion from the pancreas, and inhibiting gastric emptying.
- Exhibits trophic effects on both exocrine pancreas and gallbladder mucosa.
CCK Molecular Form and Biological Activity
- Exists in molecular forms ranging from 8 to 59 amino acids formed from a preprohormone precursor.
- The minimal active fragment necessary for function comprises 7 C-terminal amino acids.
- Requires sulfation of tyrosine at the 7th position from the C-terminal for full physiological activity.
Gastrin
- Released from G cells in the antrum and duodenum.
- Stimulated by protein digestion products, mechanical distention, and specific food items like decaf coffee or wine.
- Inhibited by acidification of the antrum.
- Following a meal, large amounts of G-17 (a form of gastrin) are released from the antrum, with smaller amounts of G-34 from the duodenum.
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Description
This quiz explores the roles of neurocrines like VIP, GRP, and enkephalins in the gastrointestinal system. It highlights their locations and specific actions, such as relaxation of gut smooth muscle and stimulation of gastrin release. Test your knowledge of these important peptides and their functions in the body.
