156. Regulation of Body Temperature and Acclimatization to Hot and Cold Environments – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• Normal core body temperature is approximately 37°C, with a usual range of 36.6–37.2°C. It is essential for normal enzyme activity, metabolism and organ function. Temperature varies with time of day, exercise, age, sex, meals, emotions, body size, sleep and environmental conditions.
• Thermoregulation is a negative-feedback process involving thermoreceptors, sensory pathways, the hypothalamus, autonomic and somatic pathways, and effector organs. The anterior hypothalamus mainly promotes heat loss, whereas the posterior hypothalamus promotes heat conservation and heat production.
• Warm and cold receptors are present mainly in the skin. Central thermoreceptors, especially those in the preoptic area of the anterior hypothalamus, monitor blood temperature. Hypothalamic thermoreceptors are much more sensitive than cutaneous receptors.
• Heat is produced mainly by basal metabolism, skeletal muscle activity, shivering, diet-induced thermogenesis and non-shivering thermogenesis. Thyroxine and catecholamines increase metabolic activity and heat production.
• Heat is transferred from tissues to the blood and then from the core to the skin. The skin is the major organ for heat exchange. Heat is lost by radiation, conduction, convection and evaporation. Radiation is the major route under comfortable conditions, while evaporation becomes most important when environmental temperature approaches or exceeds body temperature.
• Heat balance occurs when heat production equals heat loss. During heat exposure, exercise or inadequate heat dissipation, positive heat storage occurs and core temperature rises. High humidity reduces evaporation and therefore increases the risk of overheating.
• During heat exposure, cutaneous vasodilation and sweating increase heat loss. Eccrine sweating is mediated by sympathetic cholinergic fibres. Reduced physical activity and appetite also decrease heat production.
• During cold exposure, cutaneous vasoconstriction conserves heat, while shivering rapidly increases heat production. Non-shivering thermogenesis, particularly through brown adipose tissue, is important in infants. Piloerection occurs in humans but has little insulating effect.
• Heat acclimatization develops with repeated heat exposure, usually within 7–10 days. It causes earlier and greater sweating, better skin blood flow, expansion of plasma volume, reduced heart rate at the same workload and increased sodium conservation by aldosterone. These changes improve heat tolerance and reduce heat-related illness.
• Cold acclimatization involves improved peripheral blood-flow responses, altered metabolic responses and reduced heat conductance from the core to the skin. Cold-induced vasodilation and the Lewis-Hunting response help protect peripheral tissues from excessive cooling.
• Heat syncope results from peripheral vasodilation and reduced venous return, causing reduced cerebral blood flow and temporary loss of consciousness. Heat exhaustion results mainly from water and electrolyte loss with cardiovascular strain; sweating is usually profuse and body temperature is generally below 40°C.
• Heat stroke is a medical emergency characterized by core temperature above 40°C with central nervous system dysfunction such as confusion, seizures or coma. Immediate rapid cooling and supportive treatment are essential.
• Malignant hyperthermia is an inherited reaction to certain anaesthetic agents and succinylcholine, caused by excessive calcium release from skeletal muscle. It produces muscle rigidity, rapidly rising temperature, tachycardia and metabolic acidosis; dantrolene is lifesaving.
• Hypothermia is a core temperature below 35°C. Cold-water exposure causes rapid heat loss, and severe hypothermia can produce confusion, unconsciousness, arrhythmias and death.