How do hormones establish selectivity

Question

Problem:

Question 1: Describe how Ca2+ levels in the blood are regulated by hormones.

Question 2: How do the nervous and endocrine systems work together to maintain homeostasis of the body?

Question 3: Define what a hormone is.

Question 4: How do hormones establish selectivity?

Question 5: Explain how insulin regulates glucose levels in the blood.

Please provide description of your answers.