Introduction to Homeostasis

What is Homeostasis? Ability of an organism to maintain a stable internal environment, despite changes to its internal or external environment All organ systems work together to achieve homeostasis all organisms do this! http://balancewines.wordpress.com/2009/12/ http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/homeo/homeosts.shtml

Organization of a Human cells  tissues  organs  organ systems

What things in your body need to be kept within a normal range? Body Temperature Blood pressure Blood pH O2 and CO2 concentration Osmoregulation-Water balance Blood glucose Calcium levels

How does homeostasis work? Feedback pathways A cellular relay race! (dynamic equilibrium) organs and structures communicate with each other in response to changes in the body Keeps levels of certain processes within a normal range http://en.wikipedia.org/wiki/File:Southern_12_stage-02_1988.jpg all images generated by Microsoft Clip Art Gallery 7

Cellular Relay Race Stimulus Receptor Integrating center Effector Response Reverses the stimulus Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College. all images generated by Microsoft Clip Art Gallery 8

Homeostatic control systems 3 components: Monitor (receptors) Monitors send signals through sensory pathways to the coordinating centre Coordinating centre (brain) The coordinating centre sends signals through the motor pathway to the regulator to restore normal balance Regulator (muscles, glands etc.) Monitor Coordinating centre Regulator Normal balance Change in balance

Negative feedback Process by which a mechanism is activated to restore conditions to their original state It ensures that small changes don’t become too large. Why is a thermostat a negative feedback system? Conserves resources Cellular Materials Energy (ATP)

Homeostasis Example: household thermostat Room T at 22 oC T below: thermostat turns on the furnace T above: thermostat turns off the furnace http://gasfurnaceprices.co.cc/

Example: household thermostat Monitor- Thermometer Detects decrease in temperature Coordinating centre- Thermostat switches on furnace Regulator- Furnace Thermostat detects temperature increases over “normal” Furnace turns off

Dueling Mechanisms What goes up, must come down! 1. Thermoregulation Sweating (cooling) vs. shivering (warming) 2. Sugar levels insulin vs. glucagon 3. Osmoregulation (later!) Hypotonic vs. hypertonic all images generated by Microsoft Clip Art Gallery 13

Thermoregulation Core Temperature Humans have a normal temperature of around 36.2 to 37.2 degrees Celsius Above (hyperthermia): infection Below (hypothermia): cell death http://news.bbc.co.uk/2/shared/spl/hi/health/03/travel_health/diseases/html/sars.stm http://asimplebutimpossibletask.blogspot.com/

a) Heat stress monitor Thermoreceptors of the peripheral nervous system detect an increase in body temperature send message via sensory neurons to brain (central nervous system, CNS) http://flairforthedramatic.mlblogs.com/archives/2008/09/of_all_times_to_start_winning.html

ii. coordinate Hypothalamus (CNS) signals via motor nerves to sweat glands

sweat glands initiate sweating regulate sweat glands initiate sweating evaporation of sweat off the skin causes cooling blood vessels in the skin dilate dilation allows for more blood flow to the skin heat from blood is lost to the skin so blood can return to core of your body & cool the internal organs. http://www.pgbeautygroomingscience.com/functions-of-the-dermis.html

Result: body temperature returns to normal; hypothalamus turns off cooling system

A Cooling Glove  The heat extractor increases heat loss and allows the body to perform at a higher level in severe conditions.

b) Cold stress monitor - thermoreceptors message the hypothalamus using sensory neurons ii. coordinate hypothalamus sends a message via the motor neurons

iii. regulate Arterioles of the skin constrict, therefore limiting blood flow and reducing heat loss from the skin http://www.clarian.org/ADAM/doc/HealthIllustratedEncyclopedia/2/19194.htm

Smooth muscles that surrounds the hair follicles in your skin contract, causing the hair to “stand on end” trapping warm air. Skeletal muscles contract causing shivering and increasing your metabolism to make heat.

Result: body temperature increases and hypothalamus turns off the heating system

2. blood sugar levels

Dueling Hormones What goes up, must come down! Insulin Produced by -cells of the pancreas Released into circulatory system when blood glucose is high Facilitates the transport of glucose into target cells Glucagon Produced by -cells of the pancreas Released into the circulatory system when blood glucose is low Signals the liver to break down glycogen into simple glucose Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College. all images generated by Microsoft Clip Art Gallery 27

Positive Feedback

Food for thought… On average, how many organ systems are involved in each of the processes we’ve explored? Are there any organ systems that you see in all of these processes? What might happen to these pathways if just one system was not functioning properly? Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College. all images generated by Microsoft Clip Art Gallery 29