BRS Physiology

Question 1

What cells secrete gastrin?

Answer 1

G cells of the stomach

Question 2

What is the role of gastrin?

Answer 2

Increases H+ secretion by gastric parietal cells Stimulates growth of gastric mucosa by stimulating synthesis of RNA and new protein

Question 3

What are 3 stimuli for the release of gastrin?

Answer 3

Small amino acids in the lumen (phenylalanine and trp most potent) Distention of the stomach Vagal stimulation mediated by GRP

Question 4

What inhibits gastrin secretion?

Answer 4

H+ in the lumen of the stomach - negative feedback loop Somatostatin

Question 5

What are the actions of CCK (5)?

Answer 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.

Question 6

What cells release CCK?

Answer 6

I cells of the duodenum and jejunum

Question 7

What are 2 stimuli for CCK secretion?

Answer 7

Small proteins and AA Fatty acids

Question 8

What are the three actions of secretin?

Answer 8

Stimulates pancreatic HCO3- secretion Stimulates HCO3–and H2O secretion by the liver, and increases bile production. Inhibits H+ secretion by gastric parietal cells

Question 9

Secretin is secreted by what cells?

Answer 9

S cells in the duodenum

Question 10

Somatostatin responds to what and what inhibits it?

Answer 10

secreted by cells throughout the GI tract in response to H+ in the lumen. Its secretion is inhibited by vagal stimulation.

Question 11

What is the role of somatostatin?

Answer 11

Inhibits release of all GI hormones

Question 12

What cells release histamine?

Answer 12

Mast cells in gastric mucosa

Question 13

What is the role of histamine in the GI system?

Answer 13

increases gastric H+ secretion directly and by potentiating the effects of gastrin and vagal stimulation.

Question 14

Vasoactive intestinal peptide (VIP) does what to GI smooth muscle?

Answer 14

Relaxation of GI smooth muscle including Lower esophageal sphincter

Question 15

What is the importance of the interstitial cells of Cajal?

Answer 15

These act as pacemaker cells for the GI smooth muscle

Question 16

The swallowing reflex is coordinated where?

Answer 16

Medulla

Question 17

What are the 3 events that occur in swallowing?

Answer 17

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.

Question 18

What neurotransmitter mediates the LES?

Answer 18

VIP

Question 19

Describe the movement of food does the esophagus. Include primary peristalsis and secondary peristalsis

Answer 19

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.

Question 20

Heartburn can occur when dysfunction from which sphincter is occurring?

Answer 20

may occur if the tone of the lower esophageal sphincter is decreased and gastric contents reflux into the esophagus.

Question 21

What can be a cause achalasia?

Answer 21

may occur if the lower esophageal sphincter does not relax during swallowing and food accumulates in the esophagus.

Question 22

What is receptive relaxation and what signaling molecule may be involved in it?

Answer 22

The orad region of the stomach will relax for an incoming meal - CCK will increase distensibility of the stomach

Question 23

Describe the process of mixing and digestion in the stomach.

Answer 23

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).

Question 24

Gastric contractions are _____ by vagal stimulation and ______ by sympathetic stimulation.

Answer 24

Increased

Decreased

Question 25

What is the role of fat and H+ on gastric emptying?

Answer 25

Fat inhibitis gastric emptying by increasing the release of CCK ## Footnote 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.

Question 26

What is the importance of segmental contractions of the small intestine?

Answer 26

mix the intestinal contents ## Footnote 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.

Question 27

What is the importance of peristaltic contractions of the small intestine?

Answer 27

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.

Question 28

What is the gastroileal reflex?

Answer 28

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.

Question 29

What is primary tole of the Auerbach plexus (myenteric)?

Answer 29

Controls motility of the GI smooth muscle

Question 30

What is the primary role of the Meissner's plexus (submucosal)?

Answer 30

Scretion and blood flow

Question 31

What is the role of VIP?

Answer 31

It produces relaxation of the GI smooth muscle including the LES

Question 32

What is the role of Fat on gastric emptying? H+ in the duodenum?

Answer 32

Fat inhibits gastric emptying by increasing CCK release H+ in the duodenum inhibits gastric emptying by direct neural reflexes

Question 33

What is the direct pathway of gastric H+ secretion?

Answer 33

Vagus nerve innervates parietal cells and stimulated H+. ACh is the neurotransmitter.

Question 34

What is the indirect pathway of gastric H+ secretion?

Answer 34

Vague nerve innervation of G cells causes the release of gastrin

Question 36

What is the role of Histamine in digestion?

Answer 36

It is released from enterochromaffin like cells in the gastric mucosa Stimulates H+ secretion

Question 37

What is the role of CCK on the gallbladder?

Answer 37

It causes contraction of the gall bladder and relaxation of the sphincter of Oddi

Question 38

What is the process of digestion of lipids in the stomach?

Answer 38

Mixing breaks lipids into droplets Delivery of lipids to the duodenum triggers the release of CCK, thus slowing the process of gastric emptying

Question 39

What is the process of digestion of lipids in the small intestine?

Answer 39

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

Question 40

What is the process of lipid absorption in the small intestine?

Answer 40

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