Answer: The immune system.
Explanation:
At adolescence, the pituitary activates the gonads which are the ovaries in females and testicles in males. Gonads is a sex gland or a reproductive gland that produces gametes which are the sex cells and sex hormones in organisms.
Insulin is secreted into the bloodstream and flows to its target cell the liver.
Cardiac exercises! They get your heart pumping blood quicker to strengthen it! :)