Option A :
PTH is secreted in response to low serum calcium or high serum magnesium levels
Option B :
The active circulating molecule has a half-life of approximately 3–5 minutes in patients with normal renal function.
The half-life of PTH is 3 to 5 minutes, although it can vary from 1 to 21 minutes (Sabiston)
Option C :
Calcitonin, which is synthesised by the parafollicular C cells of the thyroid gland, acts as the physiological antagonist to PTH.
Option D :
The PTH-mediated renal effects to maintain calcium homeostasis are rapid, taking minutes to hours, compared to the skeletal effects, which take hours to days

Ref: Bailey & Love 28th Ed – Page 874
Sabiston Textbook of Surgery 21st Ed – Page 925
Option A :
PTH is secreted in response to low serum calcium or high serum magnesium levels
Option B :
The active circulating molecule has a half-life of approximately 3–5 minutes in patients with normal renal function.
The half-life of PTH is 3 to 5 minutes, although it can vary from 1 to 21 minutes (Sabiston)
Option C :
Calcitonin, which is synthesised by the parafollicular C cells of the thyroid gland, acts as the physiological antagonist to PTH.
Option D :
The PTH-mediated renal effects to maintain calcium homeostasis are rapid, taking minutes to hours, compared to the skeletal effects, which take hours to days

Ref: Bailey & Love 28th Ed – Page 874
Sabiston Textbook of Surgery 21st Ed – Page 925