Lab 4 Flashcards
what orientation are smooth muscle cells aligned in intestinal wall? what effect does the contraction of each layer have?
layer of circular smooth muscle cells, and longitudinal smooth muscle in the muscularis externa
circular muscles prevent food from moving backward, while longitudinal layer shortens the tract
smooth muscle of intestinal wall = single unit. what functional characteristic does single unit smooth muscle have? what anatomical features contribute?
single unit smooth muscle = visceral smooth muscle. individual muscle cells contract as a single unit. all the fibers of a single-unit smooth muscle are electrically connected to one another through gap junctions, and an action potential in one cell spreads rapidly through the whole junction to make the entire sheet of tissue to contract. bc all the fibers contract every time, no reserve units are left to increase contraction force. instead, amount of ca2+ that enters the cell determines force of contraction.
locations of smooth muscle sphincters in GI tract
upper esophageal sphincter
lower esophageal sphincter
cardiac sphincter - between stomach and esophagus
pyloric sphincter - between stomach and small intestine
sphincter of oddi - duodenum (small intestine)
ileocecal sphincter - between small and large intestine
internal anal sphincter
how are ca++ ions able to enter smooth muscle cells?
voltage-gated channels which open according to membrane potential
ligand-gated channls which are influenced by binding of chemical messengers to receptors on surface of cells
stretch-gated channels which open when the cell is elongated
why aerate the liquid?
it keeps the tissue oxygenated and helps the tissue function normally for the whole lab period
hormone that limits motility of stomach wall. what organ releases it, and what stimulates release?
motilin, released by endocrinocytes in the mucosa of the proximal small intestine, stimulated by fasting and is released every 1 and a half to 2 hours periodically
