7) The negative-feedback system of the endocrine system works much like a

 Most of the hormones released by endocrine system are regulated by negative feedback mechanism.

- Negative feedback mechanism functions to reduce the intensity of original stimulus in order to maintain homeostasis.

Explanation:

When blood calcium levels are decreased, parathyroid gland releases parathyroid hormone (PTH).

PTH acts on bone and stimulate bone resorption by promoting osteoclastic activity. It stimulates reabsorption of calcium in kidneys. PTH promotes calcitriol synthesis that acts on small intestine to increase calcium absorption.

Action of PTH increases blood calcium levels.

When blood calcium levels are increased, thyroid gland releases hormone calcitonin.

Calcitonin opposes PTH and acts to deposit calcium in the bone.

Calcitonin acts on osteoblasts and promote increase in bone mass.

Action of calcitonin decreases blood calcium levels.

it is the most commonly accepted one