Heat Regulation and Temperature

Heat Loss

• Heat loss occurs when environmental temperature is less than body temperature.
• Maximum heat is lost from the body through skin, and a small amount is lost through the respiratory system, kidney, and gastrointestinal tract.

Methods of Heat Loss

• Conduction: 3% of heat is lost through direct conduct from the body to solid objects, and 15% is lost through conduction to air.
• Radiation: 60% of heat is lost through radiation, transferring heat by infrared ray radiation from the body to other objects.

Thermogenesis (Heat Production)

• Shivering: a primary motor center in the posterior hypothalamus is activated when body temperature is low, causing shivering and producing enormous heat.
• Increased metabolic reactions: stimulated by sympathetic centers, secreting adrenaline and noradrenaline, which accelerate cellular metabolic activities and produce heat.
• Thyrotropic releasing hormone (TRH) is released by the hypothalamus, stimulating the release of thyroid-stimulating hormone (TSH) and thyroxin (T4), which accelerates metabolic activities and increases heat production.

Chemical Thermogenesis

• An increase in sympathetic stimulation or circulating adrenaline and noradrenaline in the blood can rapidly increase cellular metabolism, producing heat.
• Chemical thermogenesis is the process of producing heat through metabolic activities induced by hormones.

Temperature Regulation

• When blood with increased temperature passes through the hypothalamus, it stimulates thermoreceptors, promoting heat loss and preventing heat production.
• Heat loss is promoted by:
  • Vasodilation of skin blood vessels, increasing heat transfer to the skin.
  • Increasing sweat secretion, losing water and heat from the skin.
• Heat production is decreased by inhibiting mechanisms that cause excess heat production, such as shivering and chemical thermogenesis.

Temperature Decrease Mechanisms

• When the body temperature decreases, the temperature control system institutes opposite procedures to bring it back to normal.
• Prevention of heat loss is achieved by:
  • Skin vasoconstriction throughout the body, decreasing blood flow to the skin and preventing heat loss.
• Promotion of heat production is achieved by:
  • Stimulating mechanisms that increase heat production, such as shivering and chemical thermogenesis.