The in the brain contributes to the body's maintenance of a steady internal physiological state, called

hypothalamus; homeostasis

Explanation:

The hypothalamus is located at the base of the brain, below the thalamus and above the pituitary gland and is about the size of an almond. It is divided anatomically and physiologically into three parts: anterior, middle and posterior.

The hypothalamus coordinates most endocrine functions, exerting direct action on the pituitary gland and indirect action on other glands such as adrenal, sexual gonads, thyroid and mammary glands. It also acts on regulating temperature, appetite, thirst, sleep cycle and autonomic nervous system.

From this we can conclude that the hypothalamus in the brain contributes to maintaining the body a stable internal physiological state called homeostasis.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.