Chapter 62 - Guyton Flashcards
Layers of intestinal wall from outer to inner layer.
serosa–>longitudinal muscle layer–>circular muscle layer–>submucosa–>mucosa
syncytium
when an action potential is elicited anywhere within the muscle mass, it generally travels in all directions in the muscle
Most GI contractions occur rhythmically, as a result of which types of waves?
slow waves (these waves will initiate spike potentials which are the true action potentials that cause smooth muscle contraction)
The slowness of opening and closing of the __________ channels accounts for the long duration of the action potentials.
calcium-sodium
Factors that depolarize the membrane (make it more excitable).
stretching of the muscle, Ach, stimulation parasympathetic nerves that secrete Ach
at their endings, and stimulation by several specific gastrointestinal hormones
Important factors that make the membrane potential hyperpolarized (less excitable).
effect of NE or EPI on the fiber membrane and stimulation of the sympathetic nerves that secrete mainly NE at their endings
During which type of waves does a significant amount of calcium enter the fibers and cause contraction?
spike potentials
Two plexuses of the enteric nervous system.
myenteric - GI movements; submucosal - GI secretion and blood flow
Why might the myenteric plexus inhibit some muscles?
it inhibits the pyloric sphincter and ileocecal valve to allow emptying
_____________ most often excites gastrointestinal
activity.
Acetylcholine
_____________ almost always inhibits gastrointestinal activity.
Norepinephrine
Stimulation of parasympathetic nerves causes general ________ in activity of the entire enteric nervous system.
increase
The sympathetic fibers to the gastrointestinal tract originate in the spinal cord between segments?
T5-L2
The parasympathetic fibers to the gastrointestinal tract originate?
cranial (mainly vagus) and sacral (S2-S4) nerves
Strong sympathetic stimulation of the gut results in?
little to no movement of food through the GI tract
Primarily stimulates gastric acid secretion.
gastrin
At the same time that this hormone causes emptying of the gallbladder, it also slows the emptying of food from the stomach to give adequate time for digestion of the fats in the upper intestinal tract.
CCK
In response to gastric juice emptying into the duodenum from the stomach, this hormone has a mild effect on motility of the gastrointestinal tract and acts to promote pancreatic secretion of bicarbonate which in turn helps to neutralize the acid in the small intestine.
secretin
Functional types of movement in the digestive tract.
propulsive (peristalsis) and mixed movements
Effectual peristalsis requires an active ________ plexus.
myenteric
Splanchnic Circulation
blood flow through the gut itself plus blood flows through the spleen, pancreas, and liver
Fats absorbed from the intestinal tract are not carried in the portal blood to the liver, as with the other nutrients. What occurs with fat?
absorbed by intestinal lymphatics and then conducted to the systemic circulating blood by way of the thoracic duct, bypassing the liver
What is a major value of sympathetic vasoconstriction of the gut and splanchnic blood supply?
to provide muscles and the heart with blood during exercise, or to send blood to other tissues where it is needed during circulatory or hemorrhagic shock
