Thermoregulation

1. Thermoregulation • Thermoregulation Leads to Homeostasis • Endotherms- Mammals, birds, some reptiles, and numerous insects. • Tolerate small changes in the internal heat of the body • managed by maintaining a high metabolic rate and having a complex respiratory and circulatory system • allows for sustained activity not possible in the ectotherm • Can tolerate larger changes in the external environment (1300 -1800 Cal/day BMR) • A disadvantage for many species is the high need for calories

2. Thermoregulation - Strategies • Insulation is achieved through the integumentary system (skin, hair, feathers,...) • Adaptations that greatly conserve trapped heat • 3 layers to skin • epidermis- mostly dead tissue that continually flakes off and is replaced lower epithelial cells • provides a protective layer while acting to conserve water • Mesoderm (dermis) - houses oil glands, hair follicles, nerves, & vessels • Land vertebrates can increase warmth by raising feathers and hair follicles when cold trapping in heat - goose pimples • hypodermis- consists of a layer of fat that acts as an insulator • Thick layer is called blubber in marine mammals

3. Thermoregulation - Strategies • Circulatory adaptations • vasodilation brings blood to the skin and warms the skin • vasoconstriction shunts blood away from the skin increasing core temperature • Insects, birds and larger marine mammals can use countercurrent heat exchangers • Arteries in close proximity to veins to transfer heat throughout the length of the organism • traps heat in the core reducing loss in the extremities

4. Thermoregulation - Strategies • Cooling by evaporative heat loss • water removes heat (KE) 50 - 100x faster than air alone through evaporative heat loss • method for cooling when the ambient temperature is above body temperature • panting in many mammals and birds, perspiration in humans (sensible and insensible) • some mammals lick themselves to increase the evaporative cooling effect

5. Thermoregulation - Strategies • Behavioral responses • migration • invertebrates(insects) seek sun and shade much like ectotherms • honey bees will huddle to keep warm • Adjusting metabolic heat production • increasing muscle use through shivering • non-shivering thermogenesis (NST) - increase in the activity of mitochondria to increase metabolism • brown fat- around shoulders and neck increase the heat production in those areas

6. Thermoregulation - Strategies • Feedback Mechanisms • hypothalamus- area of brain controlling temperature receives messages from cold and warm receptors located in the skin • Acclimatization- the adjustment of an organism to a new set of conditions • changing coat or shedding • changing the density of the fat layer under the dermis • changing the amount of saturated and unsaturated lipids in the membrane to resist crystallization • production of heat-shock proteins (stress-induced protein) to help resist denaturing of proteins • Energy conservation through torpor (the reduction of activity and metabolism • can be daily (sleep) of seasonal (hibernation [winter]or estivation [summer])

7. Thermoregulation - Strategies • Ectotherms - Most invertebrates, fishes, amphibians, most reptiles, and turtles. • tolerate larger changes in internal heat • manage by seeking out places in the environment with optimal temperature • tolerate a larger range of internal temperatures • an advantage is the low need for calories (~60Cal/day SMR) • some species may use vasoconstriction and vasodilation to transfer heat • main method for thermoregulation is by behavioral responses - seeking sun and shade • Adjusting metabolic heat production • Some snakes increasing muscle use through shivering to internally incubate eggs

8. Thermoregulation - Strategies • Heat Exchange with the Environment - Adaptations