December 13, 2010 BellRinger  Read essay “behavior of homeostasis” pg  What is the difference between an ectotherm and an endotherm? Objectives  Differentiate between endotherm and ectotherm  Describe the components of a feedback system Homework:  Study for exam (Wed)

How Do They Stay so Cool? Read intro p Watch DVD “Temperature regulation in animals” Record notes in journal (use chart on p. 189)

How do different organisms maintain temperature balance? Warm-blooded (endotherms) Cold-blooded (ectotherms)

Thermoregulation (Regulation of Body Temperature) poikilotherms (cold-blooded animals)  body temperatures vary with that of the environment  e.g. reptiles, fish, amphibians

Homoiotherms (warm-blooded animals)  keep body temperature constant even in winter by increasing metabolic rate  e.g. birds, mammals Thermoregulation (Regulation of Body Temperature)

Temp Regulation - Homeostasis Why must organisms maintain internal temp balance? Enzymes!!  Enzymes speed up chemical rxns in your body  Enzymes only work under certain conditions

Body Temperature Normal internal body T is 37 0 C T above this:  denature enzymes, block metabolic pathways (denature = unravel) T below this:  slow metabolism and affect brain METABOLISM: chemical changes that occur in a cell or an organism that produce energy You will learn more about this after break!

Thermostat Temperature set on thermostat Too cool? Heater kicks on and temperature goes up Too warm? Stays off until house cools down Constant checking and turning on and off

Control of homeostasis through feedback Feedback system- cycle of events in which the status of a body condition is continually monitored, evaluated, changed, re- monitored, re-evaluated, etc.

1) receptor  sensor that responds to changes (stimuli) 2) control center  sets range of values, evaluates input and sends output 3) effector  receives output from control center and produces a response 3 basic components of a feedback system

Body Temperature Control The hypothalamus acts as a thermostat and receives nerve impulses from heat and cold thermoreceptors in the skin. There are also receptors in the hypothalamus- called central thermoreceptors. These detect changes in blood temperature.

Summary What is the difference between an ectotherm and an endotherm? What are the components of a feedback system? Homework:  Study for exam

Maintenance of Body Temperature

Epidermis Dermis Outermost layer Middle layer Innermost layer Sweat gland Blood capillaries Subcutaneous fat Receptors Erector muscle Nerve fibres Sebaceous gland Hair follicle Structure of Mammalian Skin

Vasoconstriction and Vasodilatation

Correction of overheating 1. Detected by thermoreceptors in the hypothalamus. 2. Causes vasodilation. 3. Sweating

Sweating How does it work? Heat energy in the body is used to convert the water in sweat to vapour cooling down the body.

Heat Loss Radiation: Transfer of heat via infrared rays  60% heat loss at rest Conduction: Heat loss due to contact with another surface Convection: Form of conductive heat loss

Heat Loss Evaporation  Heat transferred via water (sweat) on skin surface Evaporation rate depends on  Temperature and relative humidity  Amount of skin surface exposed 25% heat loss at rest Most important means of cooling off during exercise

Dehydration JOSH! 1% = rapid ↑ in temp (heat stroke) 2% = ↓ performance 3% = ↓ coordination 4% = headache/nausea 5% = failure of thermoregulation 6% = serious risk for collapse, permanent injury, & organ failure

Correction of overcooling 1. Detected by thermoreceptors in the hypothalamus. 2. Causes vasoconstriction. 3. Decreased sweating 4. Shivering

Keeping warm When it's cold, the muscle contracts pulls the hair up. A layer of warm air accumulates around the hair and insulates the organism. Heat retained

Shivering How does it work?

Voluntary responses In humans the cerebrum “makes” people feel cold or hot. They can then e.g. put on more clothes, eat a hot meal, exercise etc as appropriate.

Hypothermia

Summary Describe the specific pathway that is used to keep us warm. Start with the temperature receptors in the skin. Describe the specific pathway that is used to cool us off. Start with the temperature receptors in the skin.