60 Questions
What is the primary function of hydrochloric acid secreted by parietal cells in the stomach?
To sterilize the meal and begin the hydrolysis of dietary macromolecules
What is the precursor of pepsin that initiates protein digestion?
Pepsinogen
What is the role of histamine in gastric secretion?
To trigger parietal cell secretion
What is the primary stimulus for gastric secretion during the cephalic phase?
Vagal input
What is the approximate amount of gastric secretion added to the intestinal contents daily?
2.5 L/day
What is the function of the proton pump in parietal cells?
To move H+ ions out of the cell
What is the role of somatostatin in gastric secretion?
Inhibiting parietal cells
What is the function of intrinsic factor in the stomach?
To absorb vitamin B12
What triggers the release of gastrin in the stomach?
Gastrin-releasing peptide (GRP) only
What is the primary function of the pancreatic juice?
To contain enzymes for digestion
What is the consequence of the release of bicarbonate ions into the bloodstream?
Neutralization of gastric acidity
What is the purpose of the 'vago-vagal' reflex during the gastric phase?
To amplify gastric secretion
What is the effect of GIP on gastric secretion and motility?
Inhibition
Which hormone, apart from GIP, also stimulates insulin secretion?
CCK
What is the name of the hormone that is secreted by enterochromaffin cells and Mo cells in the stomach, small intestine, and colon?
Motilin
What stimulates the secretion of Somatostatin?
Acid in the lumen
What is the effect of Somatostatin on the secretion of gastrin?
Inhibition
What is the name of the hormone that is also called glucose-dependent insulinotropic peptide?
GIP
Which of the following is inhibited by somatostatin?
Gastric acid secretion and motility
What is the primary function of the enteric nervous system?
Regulation of gastrointestinal function
Which gastrointestinal peptide stimulates growth hormone secretion?
Ghrelin
What is the location of the myenteric plexus in the gastrointestinal tract?
Between the outer longitudinal and middle circular muscle layers
What is the approximate number of neurons in the enteric nervous system in humans?
100 million
What is the primary function of the submucous plexus in the gastrointestinal tract?
Sensory function and regulation of blood flow
What is the primary mechanism controlling the secretion of pancreatic juice?
Hormonal control
What is the purpose of the trypsin inhibitor secreted by the pancreas?
To inhibit trypsin activity
What is the approximate volume of pancreatic juice secreted per day?
1500 mL
What is the role of bile acids in digestion?
Fat digestion and absorption
What is the pH of the duodenal contents after the secretion of pancreatic juice and bile?
6.0-7.0
What is the mechanism by which digestive enzymes are released from the pancreas?
Exocytosis
What is the primary function of the gastrointestinal tract?
To serve as a portal whereby nutrients and water can be absorbed into the body
Which of the following glands does not drain into the oral cavity?
Pancreas
What is the purpose of lysozyme in saliva?
To protect the oral cavity from bacteria
Which section of the gastrointestinal tract is responsible for the majority of nutrient absorption?
Small intestine
What is the primary function of salivary secretions in digestion?
To initiate digestion of carbohydrates
What is the term for the passage of food through the gastrointestinal tract?
Gastrointestinal motility
What is the primary energy source for the apical H+/K+/ATPase in parietal cells?
Mitochondria
What is the effect of the meal's physical presence in the stomach during the gastric phase?
Activation of stretch receptors
What is the role of somatostatin in terminating gastric secretion?
Inhibiting parietal cells
What is the effect of pancreatic juice on digestion?
Stimulation of digestive enzymes
What is the consequence of bicarbonate ion release into the bloodstream?
Neutralization of gastric acidity
What is the primary stimulus for gastric secretion during the cephalic phase?
Vagal input
What is the mechanism by which secretin regulates pH in the duodenum?
By increasing the secretion of bicarbonate-rich pancreatic juice
What is the primary stimulus for the secretion of secretin?
Acid bathing the mucosa of the upper small intestine
What is the effect of secretin on pancreatic secretion?
It increases the secretion of bicarbonate-rich pancreatic juice
What is the half-life of secretin?
5 minutes
What is the effect of secretin on gastric acid secretion?
It decreases gastric acid secretion
What is the location of the cells that produce secretin?
Upper portion of the small intestine
What is the role of gastrin-releasing peptide in the regulation of gastric secretion?
It stimulates the release of gastrin from G cells
What is the primary function of intrinsic factor in the stomach?
It facilitates the absorption of vitamin B12 in the small intestine
What is the source of gastric lipase in the stomach?
Chief cells
What is the effect of histamine on parietal cells?
It stimulates the secretion of hydrochloric acid
What is the approximate volume of gastric secretion added to the intestinal contents daily?
2.5 L/day
What is the role of hydrochloric acid secreted by parietal cells in the stomach?
It sterilizes the meal and begins the hydrolysis of dietary macromolecules
What is the primary mechanism by which CCK exerts its trophic effect on the pancreas?
Increasing the growth and differentiation of pancreatic cells
What is the primary stimulus for the secretion of CCK in the small intestine?
The contact of the intestinal mucosa with the products of digestion
What is the effect of CCK on the motility of the small intestine and colon?
It enhances the motility of the small intestine and colon
What is the site of action of CCK in the regulation of food intake?
The cerebral cortex
What is the effect of CCK on the secretion of gastric acid?
It inhibits the secretion of gastric acid
What is the location of CCK receptors in the gut?
In the small intestine and colon
Study Notes
Gastrointestinal Function and Regulation
- The primary function of the gastrointestinal tract is to serve as a portal for the absorption of nutrients and water into the body.
- The gastrointestinal tract is divided into several parts, including the mouth, esophagus, stomach, duodenum, jejunum, ileum, cecum, colon, rectum, and anus.
Gastrointestinal Secretions
-
Salivary Secretion:
- Produced by three pairs of salivary glands (parotid, submandibular, and sublingual glands) that drain into the oral cavity.
- Contains organic constituents that initiate digestion (particularly of starch, mediated by amylase) and protect the oral cavity from bacteria (such as immunoglobulin A and lysozyme).
-
Gastric Secretion:
- Arises from glands in the wall of the stomach that drain into its lumen, and also from the surface cells that secrete primarily mucus and bicarbonate to protect the stomach from digesting itself.
- Adds about 2.5 L/day to the intestinal contents.
- Contains parietal cells that secrete hydrochloric acid and intrinsic factor, and chief cells that produce pepsinogens and gastric lipase.
- Acid secreted by parietal cells serves to sterilize the meal and begin the hydrolysis of dietary macromolecules.
-
Pancreatic Secretion:
- Contains enzymes that are of major importance in digestion.
- About 1500 mL of pancreatic juice is secreted per day.
- Contains a range of digestive enzymes, most of which are released in inactive forms and only activated when they reach the intestinal lumen.
-
Biliary Secretion:
- Arises from the liver and contains bile acids that are important in the digestion and absorption of fats.
- Stimulated by glucose and fat in the duodenum.
Hormonal Regulation of Gastrointestinal Function
-
Gastrin:
- Released by G cells in the antrum of the stomach in response to a specific neurotransmitter released from enteric nerve endings, known as gastrin-releasing peptide (GRP).
- Stimulates parietal cell secretion and increases acid secretion.
-
Histamine:
- Triggers parietal cell secretion, via binding to H2-receptors.
-
Cholecystokinin (CCK):
- Secreted by endocrine cells known as I cells in the mucosa of the upper small intestine.
- Stimulates pancreatic enzyme secretion, contraction of the gallbladder, relaxation of the sphincter of Oddi, and inhibits gastric emptying.
- Exerts a trophic effect on the pancreas and enhances the motility of the small intestine and colon.
-
Secretin:
- Secreted by S cells that are located deep in the glands of the mucosa of the upper portion of the small intestine.
- Increases the secretion of bicarbonate by the duct cells of the pancreas and biliary tract, and causes the secretion of a watery, alkaline pancreatic juice.
-
Gastric Inhibitory Peptide (GIP):
- Produced by K cells in the mucosa of the duodenum and jejunum.
- Stimulates insulin secretion and inhibits gastric acid secretion and motility.
-
Motilin:
- Secreted by enterochromaffin cells (EC) and Mo cells in the stomach, small intestine, and colon.
- Acts on G-protein–coupled receptors on enteric neurons in the duodenum and colon and produces contraction of smooth muscle in the stomach and intestines in the period between meals.
-
Somatostatin:
- Secreted by D cells in the gastrointestinal mucosa.
- Inhibits the secretion of gastrin, VIP, GIP, secretin, and motilin, and acts in a paracrine fashion to mediate the inhibition of gastrin secretion produced by acid.
Enteric Nervous System
- The enteric nervous system is a network of nerve fibers that are intrinsic to the gastrointestinal tract.
- Consists of two major networks of nerve fibers: the myenteric plexus (Auerbach plexus) and the submucous plexus (Meissner plexus).
- Contains about 100 million sensory neurons, interneurons, and motor neurons in humans.
- Is connected to the CNS by parasympathetic and sympathetic fibers but can function autonomously without these connections.
Learn about the regulation of gastric secretions, the sources of gastric secretions, and their role in digestion. Understand how the stomach protects itself from digestion and the composition of gastric secretions.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
