Lab 6 - Smooth Muscle Contraction Flashcards
How can GI smooth muscle contract independantly of the brain?
ENS (enteric nervous system)
What type of contractions are GI smooth muscle?
Phasic contractions
What type of smooth muscle is found in the GI tract?
Unitary smooth muscle (contract as a syncrinum - once contractile unit)
How is GI smooth muscle electrically connected?
Via gap junctions
How is GI smooth muscle physically connected?
Adherens junctions
What generates slow waves and functions as the pacemaker in GI smooth muscle?
Interstitual cells of cajal (ICC)
How are GI smooth muscle contractions modulated?
By modulating the force or size of contraction based on the time spent above threshold (changings in amplitude)
Does frequency of GI smooth muscle contractions change?
No
Why do you not expect to see rhythmic contractions from a strip of vascular smooth muscle?
No vascular smooth muscle will not contract rhythmically - it will contract or relax in coordinated way to change vascular resistance and regulate BP - if it were to contract rhythmically we would see fluctuations in our BP.
Why would the rate of intestinal contraction be different between preperations (between each groups smoothmuscle sample)?
Because it will depend on the part of the small intestine your section came from because proximal parts will have faster contractions (because function for digestion and mixing) whereas, distal parts will have slower contractions as they function for absorption.
What are the 3 types of muscle?
Smooth, skeletal and cardiac
What type of muscle has the fastest contractions?
Skeletal
What is the duration of smooth muscle contractions?
few seconds
What is the duration of skeletal muscle contractions?
Milliseconds but depends on the stimuli frequency (tetanus) and twitch duration depends on the fiber type
What is the duration of cardiac contraction?
Around 350ms and then very long refractory periods.
What effect did ACh have on smooth muscle contraction?
Increased in ampltitude (force of contraction)
What effect did ACh have on smooth muscle contraction in the presence of atropine?
Decrease in amplitude (representing endogenous ACh in tissue).
What is atropine?
Inhibitor of ACh
What explains the increase in smooth muscle contraction force due to ACh?
Stimualtion of Gaq signalling pathway.
Receptor activation of phospholipase C = production of IP3 = IP3 induces release of Ca2+ from SR = Ca2+ calmodulin complex forms.
= stronger contraction
What effect does adrenaline have on the rate of smooth muscle contraction?
Adrenaline is an inhibitory neurotransmitter therefore it decreases amplitude (decrease in force of contraction).
What effect does adrenaline have on smooth juscle contraction in the presence of propranolol?
Propranolol has no effect so overall decrease in ampltiude due to the adrenaline.
How does adrenaline inhibit smooth muscle contraction?
Adrenaline binds to alpha adrenergic receptors.
Why does propranolol not have an effect on GI smooth muscle contraction?
Propranolol is a beta adrenergic receptor blocker (therefore it has an effect on the heart and not GI smooth muscle).
What is IMODIUM?
An opioid drug that effects the GI opioid receptors but not the brain opioid receptors
What effect does IMODIUM have on smooth muscle contraction?
Decreases amplitude - greatest effect after several minutes (this result in lab may not relfect the repsonse in the body).
What is the physiological basis of secretory diarrhoea?
Increased isosmotic NaCl secretion making fecus more water = diarrhoea
What is vibrio cholerae?
A bacterial infection in the intestines
It acts ia adentlate cyclase - increases cAMP/PKA and has the same effects on secretion as cGMP/PKA
What receptor does IMONIUM bind to?
Gai receptor in myenteric plexus
What does IMONDIUM (opioid) inhibit?
ENS neurotransmission therefore blocking the excitatory signal and reducing contraction = slows motility
How does IMODIUM help diaherra?
it increases the time it takes food to travel through the GI tract increasing the time that absorptive processes can work = this counteracts the excess secretion
What effect would an opioid drug (such as codeine) have on intestinal motility in a person without diarrhea?
Constipation = because it increases fluid absorption too much and you will get a fluid imbalance making faeces drier and harder.
