Thermoregulation

When core temperature drops, thermoreceptors signal the hypothalamus, activating the heat-promoting center. The hypothalamus releases thyrotropin-releasing hormone, stimulating the anterior pituitary to release thyroid-stimulating hormone. This increases cellular metabolism and heat production through hormonal changes and shivering, raising core temperature back to normal.

Vasoconstriction reduces blood flow to the skin, retaining heat in internal organs and minimizing heat loss to the environment. This mechanism is activated when core temperature drops, helping conserve body warmth. By restricting cutaneous blood vessel flow, the body preserves thermal energy during cold exposure.

Epinephrine, norepinephrine, and thyroid hormones boost cellular metabolism, increasing the rate at which cells produce energy and heat. These hormones are released by the hypothalamus in response to low core temperature. Elevated metabolic activity generates significant heat production throughout the body.

When core temperature rises, vasodilation increases blood flow to the skin, allowing heat dissipation to the environment. Simultaneously, the hypothalamus activates sweat glands, and as perspiration evaporates from the skin, significant heat loss occurs. These mechanisms work together to return body temperature to normal.

Shivering involves involuntary muscle contractions that increase muscle tone and activate stretch receptors. This cycle of small contractions and stretch reflexes significantly elevates skeletal muscle activity, generating substantial heat production. The brain increases muscle tone to produce heat through this reflex mechanism.

Negative feedback mechanisms maintain core temperature by detecting deviations and triggering corrective responses. When temperature drops, the heat-promoting center activates warming responses; when temperature rises, the heat-losing center activates cooling responses. This continuous monitoring and adjustment keeps body temperature within optimal range.

Peripheral thermoreceptors in the skin and central thermoreceptors in the hypothalamus detect temperature changes and send signals to the hypothalamus. These receptors continuously monitor both external and internal temperature conditions. The hypothalamus integrates these signals and activates appropriate heat-promoting or heat-losing centers in response.