Higher Biology Metabolism and survival Thermoregulation

Todays Plan Learning Intentions – I can explain what factors can affect the metabolic rate of an organism. I can explain the difference between a conformer and regulator. I can explain how a conformer maintains its metabolic rate. I can explain why conformers have a low metabolic niche. I can explain the importance of certain behaviour responses in conformers. I can explain how a regulator maintains its metabolic rate. I can explain what homeostasis is and how it is maintained.

Control of body temperature by homeostasis Examples Ectotherm Varies with that of the environment Invertebrates, fish, amphibians, reptiles Endotherm Constant and independent of the environment Birds, mammals The hypothalamus has thermoreceptor cells that monitor body temperature by: the temperature of blood coming to the brain nerve messages from skin thermoreceptor nerve endings The thermoreceptors send messages along motor nerves to effectors which trigger corrective feedback mechanisms – which return the body temperature to normal

Ectotherms Animal that cannot control its body temperature by physiological means – its temperature varies with that of the environment reptiles amphibians fish

Endotherm Animal that can control its body temperature by physiological means A high metabolic rate generates enough heat to maintain a relatively constant temperature despite temperature variations in the external environment birds mammals

Environmental temperature (oC) Body temperature (oC) 40 30 20 10 0 10 20 30 40 50 Environmental temperature (oC) ENDOTHERM ECTOTHERM

Physiological homeostasis Thermoregulation in mammals/humans is achieved using: Receptors Thermoreceptors in hypothalamus Control centre Hypothalamus Message Nerve Impulses Effectors Skin and muscles The hypothalamus plays a vital part in temperature regulation. It acts as a thermostat and responds to nerve impulses it receives from the hot and cold receptors in the skin. In addition the hypothalamus itself contains thermoreceptors that are responsive to changes in blood temperature

Thermoregulation Hypothalamus containing central thermoreceptors Change in temperature of blood in carotid artery Nerve impulses from skin thermoreceptors Nerve impulses sent to effectors Hair erector muscles Sweat glands Skin arterioles Skeletal muscles

Thermoregulation Release sweat which evaporates using heat from body Skin arterioles Dilate and increase blood flow to skin capillaries Structure Action Effect sweat glands   Hair erector muscles skeletal muscles Release sweat which evaporates using heat from body Contract and raise hairs to trap layer of warm air next to skin Involuntary contraction = shivering, which generates heat Constrict and decrease blood flow to skin capillaries Heat loss Heat generated Heat retained

Vasoconstriction When skin arterioles constrict this is called vasoconstriction. Small arterioles just below the skin contract, vasoconstriction, less blood flows closer to the skin surface and less heat is lost by radiation Hot blood Vasoconstricton arteriole contracts Less heat lost through radiation Shunt vessel opens Skin

Vasodilation When skin arterioles dilate (open out) this is called vasodilation. Small arterioles just below the skin expand, vasodilation, more blood flows closer to the skin surface and heat is lost by radiation cooling the body Hot blood Vasodilation arteriole expands More heat lost through radiation Shunt vessel closed Skin

The action of hair erector muscles – too hot Flattening of body hair next to the skin Tiny erector muscles attached to the hair follicles are relaxed Erector muscles relaxed Skin Hair lies close to skin thin layer of trapped air

The action of hair erector muscles – too cold Raising of body hair next to the skin Tiny erector muscles attached to the hair follicles contract and pull hair up Erector muscles contracted Skin Hair lies raised above skin thick layer of trapped air insulating the body

Thermoreceptors in hypothalamus Sequence of events Overheating Overcooling Activity or stimulus Strenuous exercise Hypothermia Body temperature Rises Falls Thermoreceptors in hypothalamus Detect rise Detect fall Message to skin Vasodilation Increase sweating rate Vasoconstriction Contract hair erectors Effect Increases heat loss Decreases heat loss Message to muscles Shivering (rapid contraction) Generates heat Result Body temperature falls Body temperature rises

Can I.. Explain what factors can affect the metabolic rate of an organism. Explain the difference between a conformer and regulator. Explain how a conformer maintains its metabolic rate. Explain why conformers have a low metabolic niche. Explain the importance of certain behaviour responses in conformers. Explain how a regulator maintains its metabolic rate. Explain what homeostasis is and how it is maintained.