HSC1008 Anatomy and Physiology 2 Metabolism - Temperature Regulation PDF
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Singapore Institute of Technology
Andy Lee
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This document provides notes on HSC1008 Anatomy and Physiology 2, focusing on metabolism and temperature regulation. It includes learning outcomes, body temperature, normal and variation in core temperature, heat input and output, mechanisms of heat transfer, sweating, core body temperature and negative feedback, temperature regulation, and more.
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HSC1008 ANATOMY AND PHYSIOLOGY 2 METABOLISM - TEMPERATURE REGULATION ANDY LEE (PHD) ASSISTANT PROFESSOR FACULTY HALL #04-17 OFFICE PHONE: 6592 2524 [email protected] LEARNING OUTCOMES At the end of the lesson, you should be able to: Explain the mechanisms of heat transfer Di...
HSC1008 ANATOMY AND PHYSIOLOGY 2 METABOLISM - TEMPERATURE REGULATION ANDY LEE (PHD) ASSISTANT PROFESSOR FACULTY HALL #04-17 OFFICE PHONE: 6592 2524 [email protected] LEARNING OUTCOMES At the end of the lesson, you should be able to: Explain the mechanisms of heat transfer Discuss the regulation of temperature by the hypothalamus Discuss the hypothalamic set point and its relationship with fever Understand hyperthermia and hypothermia BODY TEMPERATURE Internal core temperature – temperature of the deep tissues of the body Sites for monitoring body temperature NORMAL BODY TEMPERATURE Ranges from 36°C to 37.5°C Rectal temperature can be 0.5°C higher than oral Fig 74-1; Guyton NORMAL VARIATION IN CORE TEMPERATURE Core temperature normally varies about 1.8°F (1°C) during the day Women experience a monthly rhythm in core temperature Core temperature increases during exercise Older is colder Core temperature may vary slightly with exposure to extremes of temperature HEAT INPUT AND OUTPUT Internal heat production Core temperature Total body heat Heat input content Heat output Heat gain Heat loss External environment Fig 17-3; Sherwood MECHANISMS OF HEAT TRANSFER Fig 17-4; Sherwood MECHANISM OF HEAT LOSS FROM THE BODY Fig 74-4; Guyton SWEATING Sweating is a regulated evaporative heat- loss process Under sympathetic nervous control Rate of heat loss can be adjusted Sweat must be evaporated for heat loss to occur CORE BODY TEMPERATURE AND NEGATIVE FEEDBACK TEMPERATURE REGULATION TEMPERATURE REGULATION Integrate Fig 17-5; Sherwood CENTRAL / CORE THERMORECEPTORS Detect change in body core temperature Located in Hypothalamus Spinal cord Abdominal viscera Great veins in the upper abdomen and thorax More receptors that detect cold than warmth PERIPHERAL THERMORECEPTORS Detect change in skin temperature Located in the skin 10x more receptors that detect cold than warm temperature INCREASING HEAT PRODUCTION Shivering is the primary involuntary means of increasing heat production Adjustments in heat production by skeletal muscles Shivering: rhythmic, oscillating skeletal muscle contractions that occur at a rapid rate of 10 to 20 per second Non-shivering thermogenesis by brown fat Increased heat production stimulated by brown adipose tissue, which is capable of converting chemical energy from food into heat HEAT-LOSS MECHANISMS The magnitude of heat loss can be adjusted by varying the flow of blood through the skin Vasoconstriction, vasodilation Heat-loss mechanisms are subject to control, largely by the hypothalamus Fig 74-2; Guyton Fig 74-3; Guyton COORDINATED ADJUSTMENTS TO COLD OR HEAT EXPOSURE The hypothalamus simultaneously coordinates heat-production and heat-loss mechanisms Sherwood CONTROL OF BODY TEMPERATURE HYPOTHALAMIC THERMONEUTRAL ZONE Core temperature can fluctuate within this range without triggering thermoregulatory effectors 36.8°C to 37.2°C Thermoneutral Zone 36.8°C 37.2°C HYPOTHALAMIC TEMPERATURE SET POINT Average set point is around 37.1°C Set point of the temperature control mechanism Body attempts to bring body temperature back to this set point Fig 74-7; Guyton SKIN TEMPERATURE CAN ALTER THE SET POINT Fig. 74-8 and 74-9; Guyton SKIN TEMPERATURE CAN ALTER THE SET POINT Fig. 74-8 and 74-9; Guyton SKIN TEMPERATURE CAN ALTER THE SET POINT The higher the skin temperature, the lower the set point The lower the skin temperature, the higher the set point Anticipatory mechanism to moderate the need for large responses FEVER Regulated increase in body temperature Shifts the hypothalamic set point FEVER Defense mechanism Prostaglandins raises the Aspirin hypothalamic set point Aspirin suppresses the production of prostaglandins Fig 17-6; Sherwood REGULATED TEMPERATURE INCREASE IN FEVER 40.2 Fever Cessation 39.4 38.9 38.3 37.8 37.2 36.7 Modified from Guyton Fig 74-11 PROCESS OF A FEVER 1. Hypothalamic set point is raised 2. Chills / feels cold / shiver 3. Body temperature reaches the new set point 4. Cessation of fever 5. Hypothalamic set point reduced to normal level 6. Vasodilatation / sweating 7. Temperatures falls BODY TEMPERATURE REGULATION Fig. 74-10; Guyton HYPERTHERMIA Elevated body temperature above normally accepted range Differs from fever in which the set point remains unchanged Exercise hyperthermia Core temperature can reach a peak value of 40°C without injury as long as heat loss mechanisms are present and effective EXERCISE HYPERTHERMIA Fig 17-7; Sherwood HYPERTHERMIA Heatstroke Beyond 40.5°C, heatstroke is likely to develop Thermoregulation overwhelmed and become seriously impaired at this temperature Lack of compensatory heat loss measure such as sweating Damage to brain, liver, kidney etc Acclimatization Increased tolerance to heat with exposure to hot and humid conditions in 1 – 3 weeks HYPOTHERMIA Lowered core temperature without reset of set point Temperature regulation is impaired below 35°C Artificial hypothermia Therapeutic hypothermia Hypothalamic activity depressed with drugs followed by cooling the patient down BODY TEMPERATURE AND HYDRATION STATUS Sawka, M. N., Latzka, W. A., Matott, R. P., & Montain, S. J. (1998). Hydration effects on temperature regulation. International journal of sports medicine, 19(S 2), S108-S110. Sawka, M. N., Montain, S. J., & Latzka, W. A. (2001). Hydration effects on thermoregulation and performance in the heat. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 128(4), 679-690. REFERENCES Chapter 17. Sherwood, L. (2016) Human Physiology: From Cells to Systems. 9th edition. Cengage Chapter 74. Hall, J. E., & Hall, M. E. (2020). Guyton and Hall textbook of medical physiology. 14th Edition. Elsevier Health Sciences.
