Thyroid vs. Parathyroid Hormone?

[torshi]

Just checking on this one

Thyroid hormones (tyrosine derivatives such as T3/T4): Decrease Ca in blood such as calcitonin and raise metabolic rate.

Parathyroid Hormones (peptide hormones/not diffusable): Increase Ca in the blood

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[MedPR]

Just checking on this one

Thyroid hormones (tyrosine derivatives such as T3/T4): Decrease Ca in blood such as calcitonin and raise metabolic rate.

Parathyroid Hormones (peptide hormones/not diffusable): Increase Ca in the blood

It's not necessary for the MCAT, but I don't think T3 and T4 regulate plasma calcium levels. They are primarily involved in metabolism.

You are correct about the functions of calcitonin and PTH, and also that PTH acts via a secondary messenger system. Also, keep in mind that PTH has a much more significant effect than calcitonin. Your body can regulate calcium perfectly fine without calcitonin, but not without PTH.