TPR CBT 1 #13-CV system

[MedChallenge]

---

Members don't see this ad.

I thought I read somewhere that cardiac contractions can become stronger as a result of a decrease in blood vessels. Is this true?

I'm referring to the question below.

13. A drug is discovered that reduces smooth muscle contraction by inhibiting response to acetylcholine. This is likely to:

A. reduce the transcription of the Na+/K+ ATPase
B. reduce the hypertensive effect of angiotensin II
C. increase the strength of cardiac muscle contractions
D. decrease renal blood flow

 

[90210]

Why don't you ever include an answer to your questions. People would like to double check if they are correct before explaining a concept they are familiar with.

 

[MedChallenge]

Why don't you ever include an answer to your questions. People would like to double check if they are correct before explaining a concept they are familiar with.

Well, I didn't here because I'm asking why an incorrect choice is wrong. But I'll try to keep that in mind for my future posts. Answer is B.

And the first sentence was supposed to say "I thought I read somewhere that cardiac contractions can become stronger as a result of a decrease *of pressure* in blood vessels. "

 

[90210]

Anyways, I think what you're referring to is regarding cardiac output and blood pressure. Usually when blood pressure drops, our body responds to that in a variety of ways. One mechanism is via the release of hormones like ADH and Aldosterone (both increase Blood Pressure). Another way our body does this is by increasing cardiac output. The faster your heart beats, the more liters of blood are pumped out. It does this to increase blood pressure.

For this question though, smooth muscle is inervated by the autonomic system which consists of parasympathetic and sympathetic systems. I'm not entirely sure but smooth muscle cells function via gap junctions and the muscle cells are excited via influx of ions like calcium which pass through one gap junction to another. This would rule out A.

For choice C, the heart is stimulated by both the sympathetic and autonomic system. The parasympathetic system decreases the heart beat via acetycholine. The sympathetic system increases the heat beat via epinephrine. When one signal dominates over the over, as is the case when you get really nervous (epinephrine >> acetycholine), your heart beats faster. A faster heat beat does not neccessarily mean a stronger heart beat. The strength of a heart beat is dependent on how much blood flows into the heart (stretches it). More stretching = more forceful heart beat. You could assume for this question that the volume of blood in the individuals body isn't changing, therefore there's no reason to expect the heart beat to increase in strength.

Choice D is somewhat connected to Choice C. For the reasons stated earlier, the heart beat increases (epinephrine >> acetycholine) due to inhibition of acetycholine. Therefore, MORE renal blood flows (per second) into the kidney via the renal arterioles. And because more flows in, more should flow out via the renal venules

Choice B is also connected the reasoning in Choice C. Angiotensin II is a precursor to the activation of Aldosterone. By activating Aldosertone, it in turn increases Blood Pressure. (Side note: It also increases blood pressure). The problem here is that a faster heat beat increases blood pressure as is so that would negate the need for angiotensin II. This is why B is true. Angiotensin II is only increased when blood pressure is detected to be really low.