Gastrointestinal Physiology Flashcards
What stimulates Peristalsis?
Distention, Irritation, and Parasympathetic Nervous System.
What is the function of Myenteric Plexus?
Myenteric system is responsible for peristalsis.
What is the direction of Peristalsis?
Myenteric plexus is itself polarized in the anal direction.
The contractile ring appears slightly on the oral side of the distention and it moves toward the distention. This is stimulated by Ach and Substance P. The gut few cms further the distension relaxes and this is caused by VIP, NO, and ATP.
What is the law of the gut?
Peristalsis and the propulsive movement in the anal direction. Movement slow downs when we age.
What does Gastrin do?
It relaxes the stomach
Mucosal growth stimulation
Stimulates the gastric acid secretion
What hormones control the GIT motility?
Cholecystokinin
Secretin
Gastric Inhibitory Peptide
What does Cholecystokinin do?
It is released from the jejunal mucosa when fatty acids are in the intestinal contents.
It causes emptying of the gallbladder.
It slows down the emptying of the stomach.
Increases pancreatic enzyme activity
Relaxes the sphincter of Oddi
Increases the secretion of pancreatic bicarbonate
Growth of Exocrine pancreas
What does Secretin do?
It is released from the duodenum when the gastric juice enters it.
It has a mild inhibitory effect on the mobility of GIT.
Stimulates biliary and pancreatic bicarbonate secretion, growth of exocrine stimulation, pepsin secretion.
What does GIP do?
It is released from the upper mucosa of the small intestine when there are fat and a lesser extent in response to carbohydrates.
It slows the motility.
It stimulates the release of insulin
What hormones inhibit the GIT motility?
VIP, NO, Glucagon, Cholecystokinin, Secretin, and GIP.
What increases the GIT motility?
Gastrin, Motilin, and Serotonin
What does Gastrin do?
Stimulates the production HCl and Pepsin
Increases the gastric motility
Relaxes the ileocecal sphincter
What does Serotonin do?
Increases the Gastric Motility
Produces by enteroendocrine cells in the stomach and EC cells in the small intestine.
What does Somatostatin do?
It inhibits the secretion.
It is secreted by D cells in GIT.
What happens to the nutrients when they enter the liver through portal vein?
Hepatocytes and Reticuloendothelial cells absorb and store 2/4-3/4 (or 50-75%) of the nutrients.
What is splanchnic blood flow?
The term splanchnic circulation refers to all blood flow originating from the celiac, superior mesenteric, and inferior mesenteric arteries, which is widely distributed to all abdominal viscera.
What increases splanchnic blood flow?
Active absorption and increased motor activity cause an increase in blood flow to about 150% for 3-6hrs.
What causes increased blood flow?
Vasodilators
Low Oxygen Concentration (to 50%, causes adenosine release)
High Metabolic Rate
What are some vasodilators?
Cholecystokinin VIP Gastrin Secretin Kallidin Bradykinin
What happens to the GIT in circulatory shock?
Greatly diminished the gastrointestinal absorptive capacity
What is the effect of the parasympathetic nervous system on the Gastrointestinal blood flow?
Increased glandular activity
Increased blood flow
What is the effect of the sympathetic nervous system on the gastrointestinal blood flow?
Vasoconstriction of arterioles with decreased blood flow.
What is Autoregulatory escape?
After a few minutes of the sympathetic activity, the blood flow comes back to normal. This is elicited by ischemia.
The sympathetic nervous system can block the splanchnic blood flow for how long?
One hour
How much blood can the sympathetic nervous system provide?
200ml to 300ml in hemolytic shock
How do the GIT muscles act as a syncytium?
The muscle fibers are connected electrically with gap junctions.
In what direction does Action potential travel in GIT muscles?
It travels in all directions.
Distance is proportional to excitability.
What kind of electrical activity is found in GIT muscle?
It is a continuous but slow electrical activity. There are two types of basic waves.
Slow waves
Spike waves
What are slow waves?
Slow waves are caused by the undulation of the pumping activity of the Na/K pump. The frequency of slow waves determines the rhythmicity of the GIT contraction. They control the spike potentials.
What is spike potential?
It is a true action potential.
What is the mass movement?
Mass movements constitute a type of motility not seen elsewhere in the digestive tube. Known also as giant migrating contractions, this pattern of motility is like a very intense and prolonged peristaltic contraction that strips an area of large intestine clear of contents.
What causes mass movements in the large intestine?
Irritation
Distention
Parasympathetic nervous system
What is ulcerative colitis?
Mass movements in the large intestine all the time
