Chapter 7 - Maintaining an Internal Balance

7.1 & 7.2

Homeostasis

• human body systems are constantly adjusting to changes in the external environment to maintain a constant internal environment

• homeostasis is an active process, sometimes called dynamic equilibrium

Optimal Human Body(Image from: http://www.liesyoungwomenbelieve.com/index.php?id=354)

• temperature: 37ºC• blood sugar level:

0.1%• blood pH: 7.35• etc.

Homeostatic Control System(Image from: http://www.revisescience.co.uk/2010/schools/ilford/abhomeostasis.asp)

• monitor• coordinating center• regulator

Feedback Systems

• negative feedback– signals coordinating centre to counteract

any detected changes in the same direction

– prevents a small change from becoming too large

Negative Feedback(Image from: http://www.freewebs.com/sandra02n/)

Negative Feedback(Image from: http://academic.kellogg.edu/herbrandsonc/bio201_mckinley/endocrine%20system.htm)

Feedback Systems(Image from: http://ingrimayne.com/econ/AllocatingRationing/PriceAndFeedback.html)

• positive feedback– signals coordinating centre to amplify any

detected changes in the same direction– much less common– causes a small change to become larger

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Positive Feedback(Image from: http://pespmc1.vub.ac.be/feedback.html)

Positive Feedback(Image from: http://biologyfiles.fieldofscience.com/2011_01_01_archive.html)

Thermoregulation

• the regulation of body temperature

• each species has an optimal temperature

Thermoregulation

• ectothermstemperature is regulated by external

temperature

• endothermscan maintain constant body temperature

regardless of external changes

Ectotherms & Endotherms(Image from: http://faculty.uca.edu/johnc/animalstructfu.htm)

Thermoregulation(Image on next slide from: http://schoolworkhelper.net/2010/07/thermoregulation/)

• In humans, the hypothalamus (part of the brain) is the coordinating centre for thermoregulation.

Image taken from: http://zaborina.i.ph/photo/108/109

Mammalian Diving Reflex

• when a mammal is submerged in cold water, the hypothalamus signals – the heart rate to slow down– blood to be diverted to the brain and other

vital organs to conserve heat

• useful in preventing hypothermia

Mammalian Diving Reflex(Image from: http://www.celticseakayaking.com/articles/mammal.htm)