a released substance that regulates the cells own function
description of neurocrine?
sensory cells secrete neurotransmitter
What are the 3 sphincters that divide the GI tract?
esophageal sphincter - prevents heartburn
pylorus sphincter - stomach to SI, when closed allows the stomach to have a high acid content
ileocecal sphincter - bewteen SI and LI, you dont want to lose partially digested food to the LI this prevents that from happening.
What is segmentation reflex and why does it happen?
mixing of digesta
contraction of circular muscle
not propagated in one direction
what is peristalitic reflex and why does it happen?
programmed by the ENS and moves food down the GI tract
it is accomplished by the contraction of longtitudinal muscle relaxation of circular muscle and then the opposite.
moves in one direction
What is the mechanism for contraction throughout the GI tract
Basic Electrical Rhythm - smooth muscle has an intrinsic rhythm of depolarization and repolarization. Frequency is stomach ever 3 min, duodenum every 12 min, ileum every 9 min
Contraction occurs when depolarization is high enough to cause an action potential
Regulation - acetylcholine increases the resting basal membrane potential and stimulates action potentials and contraction, Norepinephrine decreases the resting basal membrane potential and prevents generation of actions potentials and contraction
What is smooth and striated muscle controlled by?
smooth - myenteric nerve plexus
striated - somatic nerve
What is the function of the fundus, corpus, and Antrum of the stomach?
Fundus - store contents by adapting volume
Corpus - mixing vat for saliva, food and gastric secretions
Antrum - propulsion of food thru the pyloric sphincter to the duodenum
controlled by distention, and parasympathetic
Why is there lots of folding on the stomach?
allows the stomach to change size and stretch
Factors that increase gastric emptying?
neural control - distention of gastric wall, increased parasympathetic
endocrine control (gastrin)
factors decreasing gastric emptying?
neural control - chemoreceptor, osmoreceptor mechanoreceptor at the duodenum (hypertonicity, H plus)
endocrine control (CCK, gastric inhibitory peptide, secretin)
What is the segmentation reflex of the SI?
major type of motility
mix luminal content
regulated by ENS
What is the migrating myoelectric complex?
interrupted during feeding in carnivores but not in herbivores