Final answer:
The hypothalamus is the diencephalic structure responsible for regulating temperature, water balance, and metabolism of fats and carbohydrates. It maintains homeostasis through its control over the autonomic and endocrine systems and is linked to memory and emotion via the limbic system.
Step-by-step explanation:
The diencephalic structure involved in essential functions such as temperature regulation, water balance, and fat and carbohydrate metabolism is the hypothalamus. Located inferior and slightly anterior to the thalamus, the hypothalamus is a crucial part of the diencephalon, which also includes other structures like the thalamus.
The hypothalamus plays a significant role in homeostasis by coordinating activities through the autonomic and endocrine systems, and it does so mainly by regulating the anterior pituitary gland. It is also involved in memory and emotion through its connections with the limbic system. As the executive region for the autonomic nervous system, the hypothalamus helps maintain the body's internal balance by influencing various physiological processes.