BRS Physiology Flashcards
What cells secrete gastrin?
G cells of the stomach
What is the role of gastrin?
Increases H+ secretion by gastric parietal cells Stimulates growth of gastric mucosa by stimulating synthesis of RNA and new protein
What are 3 stimuli for the release of gastrin?
Small amino acids in the lumen (phenylalanine and trp most potent) Distention of the stomach Vagal stimulation mediated by GRP
What inhibits gastrin secretion?
H+ in the lumen of the stomach - negative feedback loop Somatostatin
What are the actions of CCK (5)?
Stimulates contraction of gallbladder and relaxes sphincter of Oddi Stimulates pancreatic enzyme secretion Stimulates growth of exocrine pancreas Inhibits gastric emptying - allowing more time for intestinal digestion Potentiates secretin - induced stimulation of pancreatic HCO3–secretion.
What cells release CCK?
I cells of the duodenum and jejunum
What are 2 stimuli for CCK secretion?
Small proteins and AA Fatty acids
What are the three actions of secretin?
Stimulates pancreatic HCO3- secretion Stimulates HCO3–and H2O secretion by the liver, and increases bile production. Inhibits H+ secretion by gastric parietal cells
Secretin is secreted by what cells?
S cells in the duodenum
Somatostatin responds to what and what inhibits it?
secreted by cells throughout the GI tract in response to H+ in the lumen. Its secretion is inhibited by vagal stimulation.
What is the role of somatostatin?
Inhibits release of all GI hormones
What cells release histamine?
Mast cells in gastric mucosa
What is the role of histamine in the GI system?
increases gastric H+ secretion directly and by potentiating the effects of gastrin and vagal stimulation.
Vasoactive intestinal peptide (VIP) does what to GI smooth muscle?
Relaxation of GI smooth muscle including Lower esophageal sphincter
What is the importance of the interstitial cells of Cajal?
These act as pacemaker cells for the GI smooth muscle
The swallowing reflex is coordinated where?
Medulla
What are the 3 events that occur in swallowing?
The nasopharynx closes and, at the same time, breathing is inhibited. The laryngeal muscles contract to close the glottis and elevate the larynx. Peristalsis begins in the pharynx to propel the food bolus toward the esophagus. Simultaneously, the upper esophageal sphincter relaxes to permit the food bolus to enter the esophagus.
What neurotransmitter mediates the LES?
VIP
Describe the movement of food does the esophagus. Include primary peristalsis and secondary peristalsis
As part of the swallowing reflex, the upper esophageal sphincter relaxes to permit swallowed food to enter the esophagus. The upper esophageal sphincter then contracts so that food will not reflux into the pharynx. A primary peristaltic contraction creates an area of high pressure behind the food bolus. The peristaltic contraction moves down the esophagus and propels the food bolus along. Gravity accelerates the movement. A secondary peristaltic contraction clears the esophagus of any remaining food.
Heartburn can occur when dysfunction from which sphincter is occurring?
may occur if the tone of the lower esophageal sphincter is decreased and gastric contents reflux into the esophagus.
What can be a cause achalasia?
may occur if the lower esophageal sphincter does not relax during swallowing and food accumulates in the esophagus.
What is receptive relaxation and what signaling molecule may be involved in it?
The orad region of the stomach will relax for an incoming meal - CCK will increase distensibility of the stomach
Describe the process of mixing and digestion in the stomach.
Slow waves in the caudad stomach occur at a frequency of 3–5waves/min. Theydepolarize the smooth muscle cells.
If threshold is reached during the slow waves, action potentials are fired, followed by contraction. Thus, the frequency of slow waves sets the maximal frequency of contraction.
A wave of contraction closes the distal antrum. Thus, as the caudad stomach contracts, food is propelled back into the stomach to be mixed (retropulsion).
Gastric contractions are _____ by vagal stimulation and ______ by sympathetic stimulation.
Increased
Decreased
What is the role of fat and H+ on gastric emptying?
Fat inhibitis gastric emptying by increasing the release of CCK
H+ in the duodenum inhibits gastric emptying via direct neural reflexes. H+ receptors in the duodenum relay information to the gastric smooth muscle via interneurons in the GI plexuses.
What is the importance of segmental contractions of the small intestine?
mix the intestinal contents
A section of small intestine contracts, sending the intestinal contents (chyme) in both orad and caudad directions. That section of small intestine then relaxes, and the contents move back into the segment.
This back-and-forth movement produced by segmentation contractions causes mixing without any net forward movement of the chyme.
What is the importance of peristaltic contractions of the small intestine?
are highly coordinated and propel the chyme through the small intestine toward the large intestine. Ideally, peristalsis occurs after digestion and absorption have taken place.
Contraction behind the bolus and, simultaneously, relaxation in front of the bolus cause the chyme to be propelled caudally.
The peristaltic reflex is coordinated by the enteric nervous system.
What is the gastroileal reflex?
The presence of food in the stomach triggers increased peristalsis in the ileum and relaxation of the ileocecal sphincter. As a result, the intestinal contents are delivered to the large intestine.
What is primary tole of the Auerbach plexus (myenteric)?
Controls motility of the GI smooth muscle
What is the primary role of the Meissner’s plexus (submucosal)?
Scretion and blood flow
What is the role of VIP?
It produces relaxation of the GI smooth muscle including the LES
What is the role of Fat on gastric emptying? H+ in the duodenum?
Fat inhibits gastric emptying by increasing CCK release
H+ in the duodenum inhibits gastric emptying by direct neural reflexes
What is the direct pathway of gastric H+ secretion?
Vagus nerve innervates parietal cells and stimulated H+. ACh is the neurotransmitter.
What is the indirect pathway of gastric H+ secretion?
Vague nerve innervation of G cells causes the release of gastrin
What is the role of Histamine in digestion?
It is released from enterochromaffin like cells in the gastric mucosa
Stimulates H+ secretion
What is the role of CCK on the gallbladder?
It causes contraction of the gall bladder and relaxation of the sphincter of Oddi
What is the process of digestion of lipids in the stomach?
Mixing breaks lipids into droplets
Delivery of lipids to the duodenum triggers the release of CCK, thus slowing the process of gastric emptying
What is the process of digestion of lipids in the small intestine?
Bile acids emulsify lipids in the small intestine, increasing the surface area for digestion. Pancreatic lipases hydrolyze lipids to fatty acids, monoglycerides, and others. Hydrophobic produces of lipid digestion are solubilized in micelles by bile acids
What is the process of lipid absorption in the small intestine?
Micelles bring the lipid digestions into contact with the absorptive surface of the intestinal cells. They will then diffuse across the luminal surface of the cells. In the intestinal cells the products are re-esterfied and packaged with lipoproteins to for chylomicrons. Transported out via exocytosis to the lymph vessels
