Which of the following hormones was discovered by James Bertram Collip?

Which of the following pairs of hormone and its associated disease is correct?

Parathormone is secreted during:

What happens when the secretion of $PTH$ (Parathyroid Hormone) decreases?

Exchange of calcium between bone and extracellular fluid takes place under the influence of certain hormones.
$(a)$ What will happen if there is an excess of $Ca^{++}$ in the extracellular fluid?
$(b)$ What will happen if there is a very low amount of $Ca^{++}$ in the extracellular fluid?

Hypersecretion of parathyroid hormone leads to: