Feedback & Thermoregulatio n

Important definitions Stimulus – change in the environment Receptor – detects stimulus Afferent pathway – carries nerve impulses to brain/spinal cord Control centre – brain, interprets impulses Efferent pathway – carries nerve impulses away from brain to effector Effector – organ that responds to stimulus Response – Adjustment due to change in environment

Positive feedback Result of an action INCREASES that action ◦eg. uterine contractions and oxytocin

Negative feedback* Result of the action DECREASES that action ◦eg. blood sugar level and insulin *most feedback systems are negative

3 homeostatic control systems 1.Thermoregulation ◦Regulation of body temperature 2.Osmoregulation ◦Regulation of blood pressure 3.Excretion ◦Regulation of waste build-up

1.Thermoregulation Heat loss is common to living things Heat is a by-product of metabolism Organisms respond to hot or cold stress differently based on their ‘bloodedness’

Ectotherm (cold-blooded) Environmental temperature regulates metabolism Popular endotherms: ◦Amphibians ◦Reptiles ◦Fish

Ectothermic mechanisms of thermoregulation Cooling: ◦Evaporation of bodily fluids ◦eg. keep skin wet to lose heat with evaporation ◦Convection ◦eg. increase blood flow to body surfaces to maximize heat loss ◦Conduction ◦eg. lie in shade or on cold surface to shed heat ◦Radiation ◦eg. radiate heat from body

Ectothermic mechanisms of thermoregulation Heating/minimizing heat loss: ◦Convection ◦eg. build insulating nest/burrow ◦Conduction ◦eg. lie on a hot surface ◦Radiation ◦eg. lie in the sun Survival in freezing conditions ◦Some fish survive in sub-zero water by making proteins that act as anti-freeze and prevent water crystals from forming

Endotherm (warm-blooded) Able to maintain constant temperature regardless of environmental changes Endotherms possess a thermostat to detect changes: ◦Hypothalamus in the brain (also coordinates nerve and endocrine function) ◦Thermoreceptors for heat loss present in skin/orifices (eg. nostrils, mouth, etc.) ◦Thermoreceptors for heat gain present in special organs in some organisms (eg. in the pit viper pits) Popular endotherms: ◦Mammals ◦Birds

Endothermic mechanisms of thermoregulation Many strategies are shared with ectotherms to cool off or warm up: ◦Convection ◦Conduction ◦Radiation Endotherms posses more physiological mechanisms for thermoregulation…

Endothermic COOLING a)Sweating ◦Liquid left on skin evaporates and takes body heat with it b)Vasodilation ◦blood vessels near body’s surface dilate (widen) ◦heat of blood is lost quickly through skin Hyperthermia – elevated body temperature due to failed thermoregulation (a fever)

Endothermic COOLING Negative feedback loop: i.Body temperature rises too high ii.Hypothalamus receives afferent signal from thermoreceptors iii.Efferent impulse reaches effector organs ◦Skin = sweating ◦Blood vessels in skin = vasodilation iv.Thermoregulators sense return of body temperature to norm and hypothalamus thermoregulation shuts off

Endothermic HEATING/reduce heat loss a)Shivering ◦muscle contractions increase metabolism and generates heat b)Vasoconstriction ◦Blood vessels near body’s surface constrict (narrow) ◦Heat of blood is maintains in body’s core (body will sacrifice extremities to preserve core organ function) Hypothermia – condition in which the body’s core temperature drops below that required for normal metabolism/body function

Endothermic HEATING Negative feedback loop: i.Body temperature drops too low ii.Hypothalamus receives afferent signal from thermoreceptors iii.Efferent impulse reaches effector organs ◦Skeletal muscles = shivering ◦Blood vessels in extremities = vasoconstriction iv.Thermoregulators sense return of body temperature to norm and hypothalamus thermoregulation shuts off