Besides the neuronal control of the body temperature, endocrine regulation also plays a role. Although less important in adults, the endocrine control is crucial in babies and young children, and in situations where acclimatization to extreme temperatures is required. Like the graphic of the neuronal control, the endocrine control of temperature regulation is divided into two parts: the reaction of the body to cold situations at the left and the adjustment to warm situations at the right.
Reaction to cold:
The posterior hypothalamus activates two endocrine systems in order to produce heat and to reduce heat loss. 1. The thyroxine control system is activated: the hypothalamus will secrete more thyroid-releasing hormone (TRH). The pituitary will react to this event by secreting thyroid stimulating hormone (TSH). TSH in turn stimulates the thyroid gland to produce and release the thyroid hormone, thyroxine.
Thyroxine enables the liver, brown fat and other body cells to increase their basal metabolism and thus to produce more heat. 2. A neuroendocrine action stimulates the medulla of the adrenal gland to secrete adrenaline. Adrenaline is a potent stimulator of the basal metabolism in the liver, brown fat and other body cells. Furthermore, adrenaline is capable of reducing heat loss by constricting the blood vessels in the skin.
Reaction to heat:
The posterior hypothalamus only minimally activates the two endocrine systems in order to reduce heat production and to enhance heat loss. The minimal activation of the thyroxine control system serves the minimal required basal metabolic rate. Similarly, the adrenal gland will secrete minimal amounts of adrenaline and thus blood vessels in the skin will relax instead of constrict, and lose heat to the environment.
Patients with hyperthyroidism suffer from heat intolerance and sweat extensively.
Adults do NOT have brown fat.
Acclimatization is physiological adjustment to a particular environment over time.