Thermoregulation

Homeostasis

Homeostasis

• organ systems are interdependent • share same environment • composition effects all inhabitants • internal environment must be kept stable • maintaining stable internal environments homeostasis –dynamic equilibrium

• •

Homeostasis

varies around a Set Point

–

average value for a variable

•

specific for each individual

–

determined by genetics normal ranges for a species

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temperature 36.7 – 37.2

Parts of Homeostatic

• Receptor

Regulation

– sensitive to environmental change or stimuli • Control or Integration Center – receives & processes information supplied by receptor – determines set point • Effector – cell or organ which responds to commands of control center

HOMEOSTATIC REGULATION • Autoregulation – cells, tissues, organs adjust automatically to environmental changes • Extrinsic Regulation – Nervous System • Fast • Short lasting • Crisis management – Endocrine System • Longer to react • Longer lasting

FEEDBACK LOOPS • Negative Feedback – output of system shuts off or reduces intensity of initiating stimulus – most often seen in the body • Positive Feedback – initial stimulus produces a response that exaggerates or enhances its effect – blood clotting & child birth

Negative Feedback

Temperature Extremes • Humans are subjected to vast changes in environmental temperatures • Enzymes operate over very narrow range of temperatures • Failure to control body temperature can result in physiological changes & damage • body has several mechanisms to maintain body temperature • Thermoregulation

Temperature

•

Core temperature

–most important body temperature –temperature of organs in major cavities –rectal temperature gives best estimation •

Shell temperature

–temperature closer to surface –skin & oral temperatures

Mechanisms of Heat Transfer

• Radiation • Conduction • Convection • Evaporation

Evaporation

• water changes from liquid to vapor

Thermoregulation

Homeostasis • Control Center – preoptic area of hypothalamus • Receptors – in skin • Effectors – eccrine sweat glands & blood vessels

Mechanisms for

Heat Loss

• • skin receptors detect increase in temperature  message sent to preoptic nucleus  heat loss center (also in hypothalamus)stimulated  sets off series of events  heat loss

inhibition

of vasomotor center  peripheral vasodilation  warm blood flows to skin’s surface  • as skin temperatures rise, radiation & convection loses increase • •

sweat glands

stimulated  increase output  evaporative loss increases

respiratory centers

stimulated  depth of respiration increases

Mechanisms for Heat Gain • skin receptors notice temperature is dropping  preoptic nucleus notificed • heat loss center inhibited • • heat gain center activated • sympathetic vasomotor center decreases blood flow to dermis of skin

vasoconstriction

reduces heat loss by radiation, convection & conduction • • blood returning from limbs is shunted into deep veins

Piloerector muscles

are stimulated  stands on end  traps air near the skin hair

Heat Gain • if vasoconstriction cannot restore or maintain core temperature  shivering

thermogenesis

begins – gradual increase in muscle tone – increases energy consumption by skeletal muscle throughout body – increases work load of muscles & elevates O 2 & energy consumption  produces heat which warms deep vessels to which blood has been shunted by sympathetic vasomotor center • can increase rate of heat generation by 400%

Heat Gain •

Non shivering thermogenesis

– long term mechanism for heat production • sympathetic nervous system & thyroid hormone produce an increase in metabolism • Heat gain center stimulates adrenal medulla via sympathetic ANS  epinephrine released liver & skeletal muscle   increases rate of glycogenolysis (break down of glycogen) in metabolic rate increases • preoptic nucleus regulates production of TRH thyrotropin releasing hormone by the hypothalamus • TRH increases production of thyroxin by thyroid gland • Thyroxin is a key hormone in control of metabolism