Lab 6: Rat intestine Flashcards
What are the smooth muscles in the small intestine called? Why is this?
They are unitary smooth muscles.
Gut smooth muscle cells are connected electrically via gap function and physically via adhering junctions. Because of electrical and physical connections, cells act together as a single unit. They are therefore called unitary smooth muscle cells
What kind of contractions are there in the small intestine?
There are phasic contractions
What are the phasic contractions of the intestinal smooth muscle caused by?
They are caused by depolarisation and repolarisation of the smooth muscle, that occur in a cycle, called the basic electrical rhythm or slow wave contractions. ICC generate slow waves and thus function as pacemakers
How does modulation of GI tract contractions occur?
This is through modulating the force (or size) of contraction based on how long the muscle cell is above threshold. The frequency of contraction doesn’t change as the ICC cels are the main trigger for the depolarisation
Would you expect to see rhythmic contractions from a strip of vascular smooth muscle?
No, it will not contract rhythmically. This is to change the vascular resistance and regulate the blood pressure. If it were to contract rhythmically, we would see fluctuations in blood pressure
The strips of rat small intestine being used today are all from one animal. Would you expect the rate of intestinal contractions to be the same in all preparations?
No - it will depend on the part of the intestine your section came from.
The intestinal contractions tend to get slower as you move down the tract, this is to allow more absorption to occur. The more proximal parts are faster
Describe your results and compare what you measured to what you know about skeletal muscle and/or cardiac muscle contraction
Smooth muscle: the duration of contractions is only for a few seconds, the exact time depends on the AP number which is caused by the level of depolarisation.
Skeletal muscle: the duration of the contraction depends on the stimuli frequency (tetanus). The twitch duration depends on fibre type.
Cardiac muscle: the duration of the contraction is 350 ms, the refractory period prevents tetanus
What was the purpose of experiment 2?
This was to determine the response of smooth muscle to ACh
What does atropine do?
This blocks cholinergic receptor
What is the effect of ACh on the smooth muscle contraction?
The rate stays about the same
What effect does ACh have on the amplitude of smooth muscle contraction?
Amplitude increased from baseline as ACh is the main neurotransmitter of parasympathetic activity of the gut
What effect does acetylcholine have on smooth muscle contraction in the presence atropine?
This is a spontaneous contraction. We should see a decrease in the amplitude as atropine blocks the effect ACh
What is the aim of experiment 3?
To determine the response of the smooth muscle to adrenaline, and to determine the receptor subtypes involved in this action
What effect does adrenaline have on the rate of smooth muscle?
The rate stayed about the same
What effect does adrenaline have on the amplitude of smooth muscle contraction?
The amplitude decreased
