 Homeostasis

What is Homeostasis?  The way the body keeps its internal environment constant, in other words, how the body “maintains a steady state”  What internal conditions need to be maintained?  Temperature  Blood Glucose levels  Oxygen and Carbon Dioxide levels  Water levels  Blood pH

Feedback Mechanisms  Feedback mechanisms are the general mechanism of nervous or hormonal regulation in animals.  Feedback occurs when the response to a stimulus has an effect of some kind (  or  ) on the original stimulus.  The nature of the response determines how the feedback is 'labelled'.  Negative feedback is when the response DIMINISHES the original stimulus  Positive feedback occurs when the response ENHANCES the original stimulus

Homeostatic Control

Positive Feedback  Response that enhances the original stimulus  Less common of the two  Most changes to our bodies “steady state” are threatening and enhancing them is NOT helpful  Examples:  During labor, a hormone called Oxytocin is released that intensifies and speeds up contractions. The increase in contractions causes more oxytocin to be released and the cycle continues until the baby is born  When a blood vessel is damaged, platelets start to cling to the injured site and release chemical that attract more platelets, where they continue to accumulate until a clot is formed

Negative Feedback  Response diminishes the original stimulus  Most common feedback loop  Examples:  When blood sugar rises, receptors in the body sense a change. In response to this, the pancreas secretes insulin into the blood, effectively lowering blood sugar levels. Once homeostasis is reached, the pancreas stops releasing insulin  Next, we are going to look at one of the bodies most important roles in keeping us alive and healthy, thermoregulation

Thermoregulation  Control of body temperature is known as thermoregulation  The normal human body temperature is 37 degrees Celsius (98.6 degrees Fahrenheit)  Too much variation results in our bodies being unable to conduct the necessary chemical reactions  Body temperature is controlled by the thermoregulatory center in the hypothalamus

Thermoregulation  A body temperature that is too low is known as HYPOTHERMIA, and can lead to death  So, how does your body try to warm you up when you get too cold?  Hair’s stand on end  Blood vessels near the surface receive less blood  Shivering  Behavioral responses

 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

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

Thermoregulation  A body temperature that is too high is known as HYPERTHERMIA and can cause dehydration, heat stroke, and possibly death  So, how does your body try to warm you up when you get too hot?  Sweating  Blood vessels near the surface receive more blood  Hairs lie flat  Behavioral responses

Thermoregulation  Sweat is produced by sweat glands. When this evaporates, it cools the skin. 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

Summarize  Write a summary at the end of your notes, making sure to discuss:  What is homeostasis?  Why is it important?  Feedback mechanisms, what are they? What are the two main types, including the components of each?  Thermoregulation