  The way the body keeps its internal environment constant  How the body “maintains a steady state”  What internal conditions need to be maintained?  Temperature  Blood pH  Water levels  Blood Glucose Levels Blood Glucose Levels What is Homeostasis?

  General mechanism of nervous or hormonal regulation in animals  Triggered when the response to a stimulus has an effect of some kind (  or  ) on the original stimulus  Type of response (  or  ) determines how we label feedback Feedback Mechanisms

  Negative feedback : When a change in the system occurs, a corrective measure occurs to bring system back towards the set point.  Positive feedback : When a change in the system occurs, a corrective measure occurs to amplify the system, moving it away from its set point Feedback Mechanisms: How do we label?

  How does your body try to warm-up when you feel cold?  Hair’s stand on end  Blood vessels near the surface receive less blood  Shivering  Behavioral responses Thermoregulation: Cold

  Hair stands on end so air currents do not get to the skin, traps an insulating layer of still, warm air next to skin  Blood vessels near the skin constrict (vasoconstriction) so less blood passes through them. This means less heat is lost by radiation. hair Blood vessel Thermoregulation: Cold

  Shivering:  Your muscles contract involuntarily, generating heat  Behavior:  Curl up, huddle, put on more clothes, drink something warm Thermoregulation: Cold

  How does your body try to warm-up when you feel cold?  Sweating  Blood vessels near the surface receive more blood  Hairs lie flat  Behavioral responses Thermoregulation: Hot

  Sweat is produced by sweat glands. When this evaporates, it cools the skin. Sweat is produced by sweat glands. When this evaporates, it cools the skin Thermoregulation Sweat gland  Hair lies flat so air currents get to the skin. Heat is lost by convection.  Blood vessels near the skin dilate (vasodilation) so more blood passes through them. This means more heat is lost by radiation.

Normal body temperature is restored Normal body temperature

Vasodilation Hairs lie flat Body sweats Normal body temperature is restored Vasoconstriction Hairs stand on end Body doesn’t sweat Shivering occurs Normal body temperature The hypothalamus detects a fall in temperature Body temperature falls Body temperature rises The hypothalamus detects a rise in temperature

  Heat Stroke: a condition marked by fever and often by unconsciousness, caused by failure of the body's temperature-regulating mechanism when exposed to excessively high temperatures. Heat Stroke Mark’s Case

Exit Ticket  Think back about Mark’s Case and the video you just watched on heat stroke and answer the following questions:  Why is Mark weak, delirious, nauseous, and disoriented (this is a straightforward answer!)?  DESCRIBE how Mark’s body initially reacted to being in extremely warm temperatures.  Why couldn’t Mark produce anymore sweat once he had been out in the sun for a long period of time? Why would his blood pressure drop and his heart rate increase?  Is thermoregulation an example of positive or negative feedback? WHY?  Turn this in BEFORE YOU LEAVE!