90 Questions
What is the primary stimulus for gastric secretion during the cephalic phase?
Vagal input
What is the primary function of bile in the body?
To dispose of cholesterol
What is the main component of bile that facilitates digestion?
Bile acids
What is the function of the proton pump in gastric parietal cells?
To move H+ ions out of the parietal cell against a concentration gradient
How much bile is secreted by the liver per day?
500 mL
What is the role of somatostatin in gastric secretion?
To inhibit G and ECL cells
What is the consequence of the release of equivalent numbers of bicarbonate ions into the bloodstream during gastric secretion?
It neutralizes gastric acidity once its function is complete
What is the process by which bile components are reabsorbed in the intestine and excreted again by the liver?
Enterohepatic circulation
What is responsible for the yellow color of bile?
Glucuronides of bilirubin and biliverdin
What is the primary function of the enzymes present in pancreatic juice?
To facilitate digestion
What is the primary means of gastrointestinal regulation?
Endocrine regulation
What is the mechanism by which gastric secretion is terminated after the meal moves into the small intestine?
The buffering of gastric acidity by the meal
What is the daily secretion volume of pancreatic juice?
1500 mL
What is the primary mechanism controlling the secretion of pancreatic juice?
Hormonal control
What is the purpose of trypsin inhibitor secreted by the pancreas?
To inhibit trypsin
What is the pH range of the duodenal contents after pancreatic juice secretion?
6.0-7.0
What is the role of bile acids in the digestive process?
Digestion and absorption of fats
What is the form in which most digestive enzymes are released from the pancreas?
Inactive form
What is the name of the polypeptide that stimulates insulin secretion when administered at blood levels comparable to those produced by oral glucose?
GIP
What is the primary function of the myenteric plexus?
Motor control of the longitudinal and circular smooth muscle layers
What is the main effect of Motilin on the stomach and intestines?
Contraction of smooth muscle
What is the role of ghrelin in the body?
Stimulating growth hormone secretion and food intake
What is the main effect of Somatostatin on the gastrointestinal system?
Inhibition of gastrin secretion
What is the main stimulant of GIP secretion?
Glucose and fat in the duodenum
What is the estimated number of neurons in the enteric nervous system in humans?
100 million
What is the name of the plexus located between the middle circular layer and the mucosa?
Meissner plexus
What is the name of the hormone that inhibits gastric secretion and motility?
GIP
What is the function of substance P in the gastrointestinal tract?
Increasing the motility of the small intestine
What is the name of the cells that secrete Motilin?
Enterochromaffin cells (EC) and Mo cells
What is the term used to describe the enteric nervous system?
The little brain
What is the primary route by which the body disposes of cholesterol?
Bile
What is the term used to describe the circulation of bile components in the body?
Enterohepatic circulation
What is the component of bile responsible for its golden yellow color?
Bile pigments
What is the primary function of the bile acids in the digestive process?
To facilitate digestion
What is the daily volume of bile secretion by the liver?
500 mL
What is the primary mechanism of gastrointestinal regulation?
Endocrine regulation
What is the primary purpose of gastric secretion in the stomach?
To sterilize the meal and initiate hydrolysis of macromolecules
What is the role of intrinsic factor in the stomach?
To enhance the absorption of vitamin B12
What type of cells in the stomach produce pepsinogens and gastric lipase?
Chief cells
What neurotransmitter triggers the release of gastrin from G cells in the stomach?
Gastrin-releasing peptide (GRP)
What is the daily volume of gastric secretion in the stomach?
2.5 L/day
What is the primary function of mucus and bicarbonate secretion by surface cells in the stomach?
To protect the stomach from self-digestion
What is the primary component of saliva that helps to neutralize gastric secretions that reflux into the esophagus?
Alkaline
Which branch of the autonomic nervous system plays the most prominent role in controlling salivary secretion?
Parasympathetic
What is the primary function of saliva in relation to taste?
To stimulate the taste buds
What is the name of the phase of gastric secretion that occurs before food is ingested?
Cephalic phase
What is the primary function of saliva in relation to mouth cleanliness?
To keep the mouth and teeth clean
What is the primary purpose of the stomach in the digestive process?
To mix food with digestive juices
What is the primary mechanism by which CCK secretion is controlled?
Positive feedback loop involving the stimulation of protein and fat digestion
What is the primary function of secretin in the digestive process?
To increase the secretion of bicarbonate-rich pancreatic juice and neutralize acid
What is the stimulus for the secretion of secretin?
The presence of acid in the duodenum
What is the effect of secretin on gastric acid secretion?
It inhibits the secretion of gastric acid
What is the primary mechanism by which somatostatin inhibits gastrin secretion?
By acting in a paracrine fashion
What is the effect of GIP on gastric secretion and motility?
It inhibits gastric secretion and motility
What is the primary site of secretion of Gastric Inhibitory Peptide (GIP)?
Mucosa of the duodenum and jejunum
Which of the following hormones is secreted by enterochromaffin cells (EC) and Mo cells in the stomach, small intestine, and colon?
Motilin
What is the effect of secretin on pancreatic secretion?
It increases the secretion of bicarbonate-rich pancreatic juice
What is the stimulus for the secretion of somatostatin in the gastrointestinal mucosa?
Acid in the lumen
What is the effect of motilin on the stomach and intestines?
It contracts smooth muscle
What is the unique property of GIP that distinguishes it from other hormones that stimulate insulin secretion?
It stimulates insulin secretion when administered at blood levels comparable to those produced by oral glucose
What is the primary function of the gastrointestinal tract?
To absorb nutrients and water into the body
What is the first secretion encountered when food is ingested?
Saliva
What is the location of the glandular structures that deliver secretions into the lumen of the intestine?
Throughout the length of the intestine
What is the role of amylase in saliva?
To initiate starch digestion
What is the importance of the surface area of the intestine?
It allows for the absorption of nutrients
What is the primary action of cholecystokinin (CCK) in the pancreatic function?
Stimulation of pancreatic enzyme secretion
What is the effect of cholecystokinin (CCK) on the gallbladder?
Contraction of the gallbladder
What is the function of immunoglobulin A in saliva?
To protect the oral cavity from bacteria
What is the effect of cholecystokinin (CCK) on gastric emptying?
Inhibition of gastric emptying
What is the primary stimulus for the secretion of cholecystokinin (CCK)?
Contact of the intestinal mucosa with peptides and amino acids
Where else is cholecystokinin (CCK) found in the body besides the I cells in the small intestine?
In nerves in the distal ileum and colon, and in neurons in the brain
What is the possible role of cholecystokinin (CCK) in the brain?
Regulation of food intake
What is the unique role of bile in the body's cholesterol disposal process?
It is the only route by which the body can dispose of cholesterol
What is the primary function of the bile acids in the digestive process?
They represent the most important components of bile
What is the term used to describe the circulation of bile components in the body?
Enterohepatic circulation
What is the composition of bile?
Bile acids, bile pigments, and an alkaline electrolyte solution
How does the body regulate the functions of the gastrointestinal tract?
Through the release of hormones triggered by meal-associated stimuli
What is responsible for the yellow color of bile?
The glucuronides of bilirubin and biliverdin
What is unique about the composition of saliva?
It is hypotonic compared to plasma
Which branch of the autonomic nervous system controls salivary secretion?
Parasympathetic branch
What is the primary function of saliva in relation to food?
To facilitate swallowing
What is the primary purpose of the stomach in the digestive process?
To store and mix food with digestive juices
What is the significance of the alkaline nature of saliva?
It helps to neutralize gastric secretions that reflux into the esophagus
What happens during the cephalic phase of gastric secretion?
The stomach readies itself to receive the meal before it is actually taken in
What is the primary action of gastrin on the stomach?
Stimulation of gastric acid and pepsin secretion
What is the source of gastrin production in the body?
G cells in the antral portion of the gastric mucosa
What inhibits gastrin secretion?
Acid in the antrum
What is the term for the local action of mediators on cells in the local area?
Paracrine
What is the function of the enteric nervous system?
Regulation of digestion and absorption
What is the connection between the enteric nervous system and the central nervous system?
Extrinsic innervation
Study Notes
Overview of Gastrointestinal Function & Regulation
- The primary function of the gastrointestinal tract is to serve as a portal for nutrient and water absorption into the body.
Gastrointestinal Secretions
- Salivary secretion:
- Produced by three pairs of salivary glands (parotid, submandibular, and sublingual glands)
- Organic constituents initiate digestion (amylase) and protect the oral cavity from bacteria (immunoglobulin A and lysozyme)
- Gastric secretion:
- Food is stored in the stomach and mixed with acid, mucus, and pepsin
- The stomach adds a significant volume of digestive juices to the meal
- The stomach readies itself to receive the meal before it is actually taken in (cephalic phase)
- Pancreatic secretion:
- Contains enzymes essential for digestion
- Bile is the only route for the body to dispose of cholesterol (either in its native form or following conversion to bile acids)
- About 500 mL of bile is secreted per day
- Biliary secretion:
- Bile acids are essential for the digestion and absorption of fats
- Bile is made up of bile acids, bile pigments, and other substances dissolved in an alkaline electrolyte solution
- Some components of bile are reabsorbed in the intestine and then excreted again by the liver (enterohepatic circulation)
Gastrointestinal Regulation
- There are three main modalities for gastrointestinal regulation:
- Endocrine regulation: hormones released by triggers associated with the meal travel through the bloodstream to change the activity of a distant segment of the gastrointestinal tract
- Paracrine regulation: mediators alter the function of cells in the local area where they are released
- Neural regulation: the intestinal system has extensive neural connections, including connections to the central nervous system and a largely autonomous enteric nervous system
- Hormones involved in gastrointestinal regulation include:
- Gastrin: stimulates gastric acid and pepsin secretion, and the growth of the mucosa of the stomach and small and large intestines
- Secretin: increases the secretion of bicarbonate by the duct cells of the pancreas and biliary tract, and augments the action of CCK in producing pancreatic secretion of digestive enzymes
- Gastric Inhibitory Peptide (GIP): stimulates insulin secretion and inhibits gastric secretion and motility
- Motilin: produces contraction of smooth muscle in the stomach and intestines in the period between meals
- Somatostatin: inhibits the secretion of gastrin, VIP, GIP, secretin, and motilin, and is stimulated by acid in the lumen
Enteric Nervous System
- The enteric nervous system is a complex network of nerve fibers intrinsic to the gastrointestinal tract
- It contains about 100 million sensory neurons, interneurons, and motor neurons
- It regulates gastrointestinal function through two major networks of nerve fibers: the myenteric plexus (Auerbach plexus) and the submucous plexus (Meissner plexus)### Hormonal Regulation of Digestion
- Gastrin secretion increases acid secretion, but the resulting acid inhibits further gastrin secretion.
Cholecystokinin (CCK)
- CCK is secreted by I cells in the mucosa of the upper small intestine.
- The main actions of CCK are:
- Stimulating pancreatic enzyme secretion
- Contracting the gallbladder
- Relaxing the sphincter of Oddi, allowing bile and pancreatic juice to flow into the intestinal lumen
- Inhibiting gastric emptying
- Exerting a trophic effect on the pancreas
- Enhancing the motility of the small intestine and colon
- CCK is also found in:
- Nerves in the distal ileum and colon
- Neurons in the brain, particularly the cerebral cortex
- Nerves in various parts of the body
- In the brain, CCK is involved in regulating food intake and is related to anxiety and analgesia production.
- CCK secretion is increased by contact between the intestinal mucosa and products of digestion, such as peptides and amino acids.
Learn about the role of acetylcholine, vagal input, and meal constituents in stimulating gastric secretion during the cephalic phase.
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