Blanketty Blanking PTH/Calcitonin confusion

[Hexon]

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by zeus' swinging testicles i swear the ppl who write these things intentionally try and make it more confusing that it should be.

so the scenario is:
a patient who has had her thyroid removed complains of nausea, tetany, numbness and tingling around her lips. Excess of what mineral most likely contributes to these symptoms?

a)PTH
b) Calcitonin
c) Phosphorus
d) Calcium,


the answer is d, calcium; the answers also expand that 'if the parathyoid glands are ensheathed within the thyroids, parathyroid must be retained to maintain calcium homeostasis'. They don't make it clear whether or not this was the case for this patient but i'm assuming it was.

but it goes on to say that 'in this case, lack of PTH leaves the serum calcium relatively unchecked, and the patient will have calcium in excess producing her symptoms'.

isn't this the other way around? PTH's role is to increase serum concentration of calcium right? if PTH is decreased, wouldn't it follow that calium would also decrease?

that's why
i picked calcitonin since i remembered that calcitonin tones down blood calcium by putting it back into bone; hence leading to calcium deficinecy in the function of nervous system and muscle contraction.

 

[SnoopDoc23]

I can definitely see your reasoning behind your answer choice. However, this is a perfect example of how the MCAT tries to get our minds running off in a certain direction and we miss some very simple key words in the question stems. If I read this question for the first time and read the answer choices, I would immediately have eliminated A and B. Reason being; Excess of what MINERAL would cause such symptoms? PTH and Calcitonin as you obviously know from describing their physiological roles, are hormones. From here I would feel confident that the calcium must be in excess without going into very deep thinking about the how and why?

But just for the hell of it...... Calcitonin acts to reduce blood calcium opposing the effects of PTH. Secretion of PTH is inversely related to [Ca2+]. Only calcitonin causes a decrease in plasma concentration of calcium, when compared to PTH and Vitamin D. Also, calcitonin is synthesized and secreted from the Thyroid gland while PTH is synthesized and secreted from the parathyroid gland.

 

[salim271]

seems like a weird question with a lacking explanation. Still, mineral is the key word, calcium is the only one that makes sense. PTH and Calcitonin are both peptide hormones.

 

[Hexon]

gotcha😉

answer just seemed confusing especially when they went on about decreasing PTH levels

 

[whiteshadodw]

i agree. mineral pretty much gives it away, and the tetany part:

http://en.wikipedia.org/wiki/Tetany_(action_potential_summation)

 

[Hexon]

wouldn't tetany and tingling arise form calcium deficiency as opposed to PTH deficiency?

 

[Majik]

wouldn't tetany and tingling arise form calcium deficiency as opposed to PTH deficiency?

Tetany occurs when the muscle is constantly being contracted. A tetany is the strongest possible contraction. Any type of muscle contraction requires calcium influx into the sarcolemma, so this alone should have led you to choose D. Moreover, C cells of the thyroid which release calcitonin are essential to keep calcium levels down. In the absence of this hormone, calcium levels go unchecked and begin to rise quickly. This explains the symptoms the patient is experiencing.

 

[Hexon]

Tetany occurs when the muscle is constantly being contracted. A tetany is the strongest possible contraction. Any type of muscle contraction requires calcium influx into the sarcolemma, so this alone should have led you to choose D. Moreover, C cells of the thyroid which release calcitonin are essential to keep calcium levels down. In the absence of this hormone, calcium levels go unchecked and begin to rise quickly. This explains the symptoms the patient is experiencing.

thanks majik, for the clarification; c cells of the thyroid keep calcium levels down