Human Body Thermoregulation Quiz

Pathophysiology of the febrile reaction and acclimatization to temperature variation

• The study covers the pathophysiology of febrile reaction and acclimatization to temperature variation.
• Homeothermy involves maintaining a constant internal body temperature, regardless of ambient temperature fluctuations or physical exertion.
• Normal body temperature is around 37 ± 0.6°C, with variations across different measurements (oral, rectal, axillary).
• A typical oral temperature is approximately 36.7°C.
• Rectal temperature readings are typically 0.5°C higher than oral readings.
• Severe or prolonged physical effort can increase body temperature to 38°C.
• The body's temperature fluctuates throughout the day, with lower values in the morning (around 3 a.m.) and higher values in the evening (around 6 p.m.).
• Temperature is the difference between heat production and heat loss.
• Thermoregulation is maintained by the nervous system, blood vessels, skin, and behavioral responses.
• The hypothalamus regulates thermoregulation.

Contents

• Homeothermy
• Febrile reactions
• Acclimatization to heat and hyperthermia
• Acclimatization to cold and hypothermia
• Local effects of cold

Body Temperature Regulation

• The body's core (muscles and viscera) produce most of its heat. Subcutaneous tissues transmit heat one-third less efficiently than other tissues.
• Heat transfer from the core to the skin occurs through blood circulation.
• Without the mechanisms for heat loss, the human body would overheat by 10°C/h during exertion, and 20°C/h.
• The hypothalamus (H) is the central thermoregulatory control center.
• The anterior hypothalamus coordinates heat loss.
• The posterior hypothalamus coordinates heat production.
• There are receptors in the anterior hypothalamus and other areas, sensitive to heat and cold.

Thermoregulation Centers

• Neurons in the anterior hypothalamus are irrigated by a rich vascular network called the OVLT.
• Endothelial cells of the OVLT release arachidonic acid metabolites, producing fever.
• The activity of thermoregulation centers is affected by various stimuli from the periphery, hormones (e.g., thyroxine, corticosteroids), catecholamines, and blood temperature.

Mechanisms for Adapting to Temperature Variations

• For temperature decrease: vasodilation, sweating, decreased heat production.
• For temperature increase: vasoconstriction, piloerection, increased heat production.
• Temperatures outside the 35.8°C to 37.4°C range indicate a thermoregulation failure.

Factors Affecting Body Temperature

• Age
• Gender
• Time of day
• Physical activity
• Environment
• Illness
• Hormones
• Diet
• Hydration
• Sleep

Thermogenesis

• The fight against cold is a chemical mechanism. Shivering increases heat production by 6-7 times.
• Activation of the sympathetic system increases cellular metabolism, releasing adrenaline and noradrenaline when temperature drops, influencing cellular metabolism.
• ATP production decreases, and heat production increases.
• Hypothalamic TRH secretion increases thyroid hormones.

Thermolysis

• Heat loss through the skin, primarily through arteriovenous shunts (like radiators).
• Peripheral vasoconstriction directs blood from superficial to deeper tissues.
• Heat loss through piloerection contractions, conduction, convection, radiation, evaporation, and respiration.

Blood Flow Control

• Blood flow is regulated by the sympathetic nervous system.
• Reducing the exchange surface area via piloerector muscle contraction reduces heat loss.
• Heat loss occurs through conduction (3%), radiation (60%), convection (15%), and evaporation (insensible perspiration, 22%). Heating and humidifying inspired air and urine/feces contribute to heat loss.

Types of Fever

• Intermittent: temperature returns to normal at least once a day, significant differences between morning and evening.
• Remittent: temperature differences greater than 20°C between morning and evening and doesn't return to normal.
• Continuous: temperature variations are less than 1°C.
• Recurrent: episodes of fever alternating with periods of normal temperature.
• Irregular: shows temperature variations of varying degrees and patterns.

ACCLIMATIZATION TO HIGH TEMPERATURES

• Thermolysis is done via cutaneous vasodilation and sweating.
• Decreasing skeletal muscle tone decreases thermogenesis.
• Exceeding adaptation mechanisms results in hyperthermia.
• Examples of heat-related illness include "heat stroke".

Heat Stroke

• Prolonged exposure to direct sunlight and significant overheating.
• Symptoms include headache, dizziness, nausea, and loss of consciousness.
• Core temperature above 40°C. Absence of sweating.
• Heat stroke is a severe thermoregulatory disorder resulting in a significantly high core temperature and lack of sweating.

ACCLIMATIZATION TO LOW TEMPERATURES

• Thermolysis is reduced via cutaneous vasoconstriction.
• Thermogenesis increases via increased skeletal muscle tone (shivering) and increased biological oxidation rate (catecholamines, thyroxine).
• The circulatory changes respond to sympathetic stimulation.
• Excessive adaptation leads to hypothermia.

Hypothermia

• Defined as a decrease in body core temperature below 35°C.
• Can be classified as mild, moderate, or severe based on temperature.
• Risk factors include extreme age, homelessness, malnutrition, chronic alcoholism, mental illness, and use of sedative medication.
• Pathogenesis involves excessive heat loss due to accidental exposure to cold, burns, increased blood circulation in the skin, or reduced metabolic rates.

Local Effects of Cold

• Direct and indirect effects on cells and extracellular fluid.
• Crystallization of water reduces cellular damage in tissues like ligaments and tendons.
• Irreversible denaturation of cell membranes is caused by increased ionic concentration.
• Blood vessel damage can lead to cellular ischemia and hypoxia.
• Vasoactive mediates (like histamine) increase capillary permeability, leading to water retention in interstitium and extensive tissue changes.

Hyperthermia

• A condition characterized by a progressive increase in internal body temperature without any changes to the set point of thermoregulatory centers.
• This disorder can be caused by exposure to a high-temperature external environment (exogenous), or arise internally (endogenous).
• Different types include heat cramps, heat exhaustion, heat syncope, and heat stroke.

Other topics covered include:

• Factors causing febrile reactions (exogenous and endogenous pyrogens).
• Effects of endogenous pyrogens (central and peripheral effects).
• Unfavorable long-term effects (e.g., muscle catabolism and toxic effects).
• Manifestations of febrile reactions (cardiovascular, respiratory, digestive, nervous, metabolic, and humoral).
• Role of fever in the body.

Test your knowledge on how the human body regulates temperature with this quiz. Learn about factors influencing thermoregulation, temperature variations, and the physiological responses involved. Perfect for students studying human physiology or related fields.