Final answer:
Antagonistic hormones have opposing effects on physiological processes in the body, such as calcitonin and parathyroid hormone affecting calcium levels in osseous tissue, and insulin and glucagon regulating blood-glucose levels through negative feedback.
Step-by-step explanation:
Two hormones that counteract one another's actions in a feedback circuit are said to be antagonistic hormones. With regards to osseous tissue, one well-known example of antagonistic hormones are calcitonin, secreted by the thyroid gland and parathyroid hormone (PTH), secreted by the parathyroid glands. Calcitonin helps to lower blood calcium levels by inhibiting osteoclast activity and promoting calcium deposition in bones, while PTH does the opposite by increasing osteoclast activity and releasing calcium into the bloodstream.
The regulation of blood-glucose levels is another example of antagonistic hormones at work. Insulin and glucagon are pancreatic hormones with opposing actions. Insulin decreases blood glucose levels by promoting the uptake of glucose by body cells and the storage of glucose as glycogen in the liver, whereas glucagon increases blood glucose levels by stimulating the conversion of glycogen to glucose in the liver. This is a classic case of negative feedback regulation where an increase in one hormone typically results in the reduction of the other, maintaining homeostasis.