Homeostasis PP 2 Feedback and Thermoregulation Introduction Mark

Homeostasis PP 2 – Feedback and Thermoregulation

Introduction �Mark Dorrity – 1988 Wagga Fun Run (https: //bit. ly/2 q. E 5 ULc)

Homeostasis �maintaining a stable internal environment �by detecting and responding to changes in the environment �Temperature, water content, chemical levels such as glucose, Ph �mechanisms involved in homeostasis homeostatic mechanisms �In complex organisms, �most of the body's systems and organs are involved �particularly nervous and endocrine (hormone) systems

Causes to change in internal environment �Minor fluctuations around an optimal level occur continuously, but things that cause big changes to the internal environment are; �Extremes in external environment (Temp or change in concentration of substances) �Diseases �Trauma (Injury) �Inherited disorders �Toxic substances

Stimulus Response Model Receptor Stimulus CNS/Endocrine System Response Effector

Thermoregulation �Different animals have different set points for their internal body temperature. �Humans 37 degrees C �Birds 41 degrees C �Cats 39 degrees C �Giant anteater 32 degrees C (lowest temp of a mammal) �Above the set point, enzymes can denature and metabolism fails. The first organ to be affected is the brain

Negative Feedback �Negative feedback cancels or counteracts the stimulus, returning the internal environment back to the set point

Feedback mechanism in thermoregulation in endotherms Temp receptors in skin Temp receptors in blood Thermoregulatory Centre is the hypothalamus in the brain. It stores an optimal temp and initiates homeostatic mechanisms if the temp deviates from normal Effector Nerves Arterioles in skin (vasodialate) Muscles of hairs (trap air) Sweat glands (evaporation) Salivary glands (panting, evaporation) Adrenal gland, lowers metabolic activity Thyroid gland, increases metabolic activity

What do you do when you are cold? �And what do you do when you are hot?

Also Behavioural and structural mechanisms Cool down �Seek shade �Inactive in heat of the day �Wallabies lick their wrists – evaporation �Remove clothing Warm up �Penguins rotate in their huddles �Lizards on rock �Polar bears black skin and clear hair �Arctic fox much smaller ears than other foxes �Blubber in marine mammals

Endotherms vs Ectotherms �Endotherms - Within heat �Some moths and beetles can raise their body temp by short periods of vigorously flapping their wings – inc internal heat by muscular activity �Mammals, birds and fast swimming fish like tuna, retain the heat generated by metabolic activity within their bodies

Endotherms vs Ectotherms �Ectotherms - Outside heat �Animals such as fish and reptiles depend on absorbing heat from the external sources �Some ectotherms are able to maintain a relatively stable internal temperature by behavioural means

Homeothermic vs Poikilothermic Homeotherms �An animal that can maintian a relatively constant temperature Poikilotherms �Many fish and most invertebrates cannot control their body temperature and therefore it changes with the external environment.

The science of heat �In hot conditions, endotherms need to reduce heat or increase hear loss �In cold conditions they need to reduce heat loss, or increase heat gain �Hibernation – when temp is too low, body resets its set point so that metabolic rate falls to a level just sufficient to sustain life. �http: //www. arkive. org/little-brown-myotis/myotislucifugus/video-00. html

The science of heat Conduction �Heat from hotter object to a cooler object via contact Convection �Warmed air/water rising and being relaced by cooler Evaporation �Water changes from liquid to vapour �Heat is required for this to occur Radiation �Transfer from hot object via infra red waves