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Temperature regulation
The document discusses temperature regulation in humans, emphasizing the mechanisms of heat loss and gain, thermoregulatory reflexes, and the role of the hypothalamus in maintaining body temperature. It outlines various temperature-related conditions such as fever, heat exhaustion, heat stroke, and hypothermia, detailing the physiological responses and control mechanisms involved. Additionally, it highlights the importance of behavioral adaptations and endocrine responses in temperature management.
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Temperature regulation
- 1. Temperature Regulation DrElizabeth J Prof & HOD Dept of Physiology AIMS &RC , Bangalore 4 / 09 /14
- 2. Scheme • Introduction • General Considerations • Mechanisms of heat loss & heat gain • Control of heat production, by radiation, conduction & evaporation • Skin &Temperature regulating reflexes • Thermoneutral Zone • Control mechanisms of temperature regulation • Fever & Hyperthermia • Heat exhaustion, heat stroke & hypothermia
- 3. Introduction • Homeothermic-Humans capable of maintaining their body temperatures within narrow limits. • Poikilothermic- (Cold blooded) • Biochemical reactions do not fluctuate due to the constant & high temperatures. • 410 C (1060F) – 430C convulsions are seen • Nerve malfunction & protein denaturation seen with higher temperature.
- 4. General Considerations Temperaturecan be expressed as 0C or 0F. C = ( F - 32) x 5/9 and F = (C x 9/5) + 32 Normal is 370C or 98.60F • Measured under tongue, axilla or rectum • Oral temp is 0.50C less than core body temperature (rectal temp). • Internal temp varies with activity pattern and changes in ext temp. • Circadian fluctuation of about 10C - lowest at night and highest during the day. • Women show higher temp during second half of menstrual cycle
- 5. General Considerations Consideringtemp as a measure of heat concentration Total heat content gained / lost by the body is determined by NET DIFFERENCE in heat produced and lost STEADY STATE- heat production must equal heat loss
- 6. Mechanisms of heatloss / heat gain • Radiation- Surface of all objects emit heat in form of Electromagnetic radiation. Rate of emission α Temperature • Conduction- Loss/ gain by transfer of thermal energy during collisions between adjacent molecules – Heat is conducted from Molecule to Molecule
- 7. Mechanisms of heatloss / heat gain • Convection- Conductive heat loss or gain is aided by movement of air / water next to body. -Cool air replacing warm air. • Evaporation- Water evaporates from skin & membrane lining the respiratory tract MAJOR PROCESS for Loss of body heat. • 600Kcal/L reqd to transfer water from fluid to gaseous state. - Heat reqd to evaporate water from the surface is conducted from the surface cooling it.
- 8. SKIN & ITSROLE • Skin is not a perfect insulator • Temp of outer surface of skin is between external temp & core temp. (net conduction = 0) • Skin acts as insulator by change in blood flow. • The heat from within is brought out by the blood and lost to the outside. • Vasoconstrictor sympathetic nerves firing rates – in response to cold & – in response to heat
- 9. Temperature – Regulatingreflexes • Thermoreceptors detect changes in the balance between heat loss & production due to metabolic rate (exercise). • Two types – Peripheral on Skin – Central in hypothalamus (integrating center), spinal cord, abdominal organs. • Output from hypothalamus is sent to effectors via – sympathetic nerves to sweat glands, – skin arterioles & adrenal medulla. – Motor neuron to skeletal muscles. • Core temp is maintained relatively constantly. • Peripheral thermoreceptors help identify heat & cold.
- 10. Thermoneutral zone(TNZ) •All the mechanisms are Graded and not All or None responses. • 250C to 300 C or 750F to 860F is known as a thermoneutral zone. • At temps lower than this TNZ max vasoconstriction cannot prevent heat loss from exceeding heat production & this requires the body to increase heat production. • At temps above this TNZ max vasodilation cannot eliminate the heat as fast as it is produced & this requires another heat loss mechanism ‘SWEATING’
- 11. Control Mechanisms ofTemperature Regulation • Nervous Mechanisms – Thermoregulatory centers • Direct Action • Reflex Mechanisms • Efferent Nerves – Endocrine and Temperature Control • Adrenal Medulla • Adrenal Cortex • Thyroid • Behavioral & Voluntary control
- 12. Scheme • Introduction • General Considerations • Mechanisms of heat loss & heat gain • Control of heat production, by radiation, conduction & evaporation • Skin &Temperature regulating reflexes • Thermoneutral Zone • Control mechanisms of temperature regulation • Fever & Hyperthermia • Heat exhaustion, heat stroke & hypothermia
- 13. Hypothalamus control •Warming of anterior hypothalamus (Heat loss) – Vasodilatation – Sweating – Hyperpnoea – Injury abolishes the heat loss responses to hot environment. • Stimulation of Posterior hypothalamus (Heat production) – Vasoconstriction – Injury abolishes responses to cold & interferes with the responses to heat. • Preoptic region of Ant. Hypothalamus is regarded as the thermostat. • SET POINT is maintained by this region
- 14. Hypothalamic temperature Regulation(contd) • Direct action: When environmental temp – Is high, warm blood flowing through hypothalamus causes HEAT LOSS responses. – Is low, cool blood causes HEAT PRODUCTION / CONSERVATION responses.
- 15. Hypothalamic temperature Regulation(contd) • Reflex Mechanisms – Sensitive thermoreceptors • in the skin carry information via cutaneous nerves and hypothalamus – Efferent Nerves • Autonomic – Sympathetic adrenergic vasomotor nerves (cutaneous vasoconstriction & vasodilatation) – Sympathetic cholinergic nerves to sweat glands • Somatic – Nerves to skeletal muscle ( tone, activity, shivering) – Nerves to respiratory muscles
- 16. Endocrine control •Adrenal medulla- – immediate adrenaline release (Calorigenic) – Exposure to cold leads to • Cutaneous vasoconstriction the heat loss • metabolic rate & heat production • Adrenal Cortex – BMR is low in adrenal cortical insufficiency – Patients do not tolerate cold well & body temp is subnormal. • Thyroid – Calorigenic – Permissive action on adrenaline calorigenesis – Hyperthyroidism-skin is warm
- 17. Behavioral and VoluntaryControl • Animals move from warm to cold regions • Curling up of body in cold conditions • Clothing in woolens in winter and thin cotton clothing in summer. • Fans, air conditioners, heaters & central heating
- 19. Control of heatproduction Response to exposure to cold Shivering thermogenesis - This contains rhythmical oscillatory muscle contractions. - No external work is involved, all the energy liberated by the metabolic machinery appears as internal heat. Non shivering Thermogenesis - Increase in (metabolic rate) heat production not due to muscular activity. - Increased epinephrine, sympathetic activity to adipose tissue & contribution of thyroid hormone.
- 20. Temperature regulating mechanisms Skin temperature Cerebral cortex “ Voluntary” motor responses Core temperature Peripheral thermoreceptors Hypothalamus Central thermoreceptors Via sympathetic nerves Adrenal medulla Sweat glands Skin arterioles Skeletal muscles Epinephrine “Involuntary” motor responses
- 21. Effector mechanisms inTemperature Regulation STIMULATED BY COLD Desired Effect Mechanism Decreased Heat Loss Vasoconstriction of skin vessels Reduction of surface area (curling up) Behavioral responses( warm clothes) Increased Heat Production Increased muscle tone Shivering & increased voluntary activity Epinephrine secretion (minimal) Increased appetite
- 22. Effector mechanisms inTemperature Regulation STIMULATED BY HEAT Desired effect Mechanism Increased Heat Loss Vasodilation of skin vessels Sweating Behavioral response Decreased Heat Production Decreased muscle tone Decreased secretion of epinephrine (minimal) Decreased Appetite
- 23. Fever & Hyperthermia • Fever is an elevation of body temperature due to a “resetting of the thermostat” • > 990F • Bacterial / Viral Infections, trauma,lesions of CNS, exposure to high temperatures & drug induced. • Increased heat production by shivering (rigor) & increased metabolism • Diminished heat loss by vasoconstriction • Skin is warm & flushed • Subsides by sweating
- 24. INFECTION LIVER MACROPHAGES IL-1, IL-6 Firing of neural receptors MULTIPLE ORGANS MACROPHAGES IL-1, IL6 HYPOTHALAMUS TEMP SET POINT Skeletal Muscles Shivering Curling up SKIN ARTERIOLES VASOCONSTRICTION HEAT PRODUCTION HEAT LOSS Heat production greater than heat loss Heat retention BODY TEMPERATURE
- 25. Heat Exhaustion •Heat waves in a humid atmosphere • Increased sweating with water and salt loss. • Headache, dizziness, cramps, vomiting and rise in temperature. • Skin is cold & clammy • Fall in BP, circulatory collapse & stupor. • Treated by fluids & electrolytes
- 26. Heat Stroke •Serious Condition,high environmental temp • Overheating of body, impaired sweating • Headache, restlessness & mental confusion • Hyperpyrexia (410C or 1060F) • Delirium, convulsions,CV collapse & COMA • Death results if untreated • Temp to be brought down to 1020C with ice packs
- 27. Hypothermia • Reductionin temp < 350C • At 270C the metabolism is greatly reduced (<280C unable to correct by itself) • HR,BP & RR are decreased • Unconscious state • Exposure to low temps • Cardiac surgery where heart is stopped