The primary purpose of which human organ system is to produce hormones that regulate body functions

The endocrine system.

This system includes the pituitary gland, thyroid gland, parathyroid gland, adrenal glands, tested/ovaries, and the pancreas.

When the ball is rising up, it gains kinetic energy. when the ball reaches the very top, it will have all potential energy, until it falls back down and gains it kinetic energy. finally when you catch the ball or it falls back down, it would have gained its potential energy back.