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Author Archives: Tom Shannon
The Effect of Class I Anti-Arrhythmics
I’ve been asked quite a bit about the effect of class I anti-arrhythmic drugs. The three subclasses of these drugs have different effects but they share one thing in common: they block Na channels. Na channels in ventricular and atrial cells … Continue reading
Why Do the Atria Beat at a Faster Rate with Heart block?
I’m getting this one a lot: I have a question regarding #28 on one of your old exams: “If the AV node is destroyed then it is expected that…” I understand that “b) the ventricles will beat at a slower rate than … Continue reading
The Effect of Exercise on Mean Arterial Pressure
I’ve been asked several times about question 27 on page 46 of the week 4 course notes. The question asks about the steady state MAP during vigorous exercise. The answer is that MAP is increased. The problem is that, as most of you will … Continue reading
The Effect of Class IB Anti-Arrhythmics on Action Potential Propagation
I’ve been asked several times about this because I put a question on the practice exam related to it. In retrospect, I wish that I hadn’t used the class IB as the example on this question and I will change … Continue reading
Where Does Ventricular Systole Start and End?
I’ve been asked this question several times now and it’s not unreasonable. I have some thoughts: This is kind of a grey area and it depends upon the context when asking the question. “Ventricular systole” when you are a physician doing … Continue reading
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How Can the Conductance be Greater For K+ than for Na+ But the Currents Be Equal and Opposite?
I’m getting this one a lot. Its #21 in the on exam questions after the Synaptic Transmission lecture but #7 after the resting potential lecture is similar: A membrane is permeable to Na+ and K+ only and the equilibrium potential … Continue reading
The IGF-1/Growth Hormone Negative Feedback System
I’ve been asked about this question at the end of the Growth Session Notes several times: A 7 year old child is given a drug that alters the action of growth hormone on the liver. Late studies reveal that the child’s … Continue reading
The Time Course of PTH Actions
I was asked to post an explanation for the following question by some students after today’s workshop. I was told that a number of students didn’t understand the answer. The question is found at the end of my Growth Self-Study: … Continue reading