Which brain structure functions to control the autonomic nervous system and to regulate body temperature?

Hypotahlamus

Explanation:

Hypothalamus has a very critical role in regulating and maintaining the homeostasis of the body and all its cell. It controls the autonomic nervous system, endocrine system and sleep wake cycle of the body. It responds to variety of signals ranging from the emotions, body temperature, and sensations of hunger and thirst to blood pressure and stress through secretion of hormones itself or by stimulating pituitary gland or pineal gland.