Homeostasis
Homeostasis is like your home’s thermostat
Thermostat’s set point is 75ºF
Inside temperature =
heat
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• Definition: The body maintains a constant internal environment
• Importance: Body processes work best in specific conditions
Control System• Sensors
– Gather information about the internal and external environment• Ex: pressure sensors in your foot
• Communication system– impulse (message) sent through the
body • Ex: nerves connected from foot to
brain.• Control Center
– Interprets sensory information• Ex: Brain interprets pain in foot.
• Targets– Body part that receives the final
message• Ex: Muscles in foot, muscles in jaw
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Negative Feedback Loops• Reverses any change
that moves conditions from a set point
– Ex: if your temp drops…you will shiver to reverse that
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Negative Feedback Loops• Reverses any change
that moves conditions from a set point
– Ex: if your temp drops…you will shiver to reverse that
– Ex: If your temp rises…you will sweat to reverse that
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Negative Feedback Loop: Cold Response
Positive Feedback Loop• Increases the changes
away from set points• Important when rapid
change is needed• Ex: Pregnancy
contractions– Uterus contractions
begin slowly– Oxytocin released to
speed up the contractions
More examples…• Growth hormones stimulate cell division• Torn vessel stimulates release of clotting factors
platelets
fibrin
white blood cellred blood cell
blood vessel
clot
Positive Feedback Loop
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Working Together
• Thermoregulation: Maintenance of body temperature– Skin (sensors): sensors detect cold– Nervous system (communication system): electrical impulse sent
to brain– Hypothalmus in brain (control center): releases hormones into
blood stream– Muscles (target) : Hormones cause shivering
• Some disruptions are temporary– Infections, fever, sore
throats, muscle soreness• Some disruptions are too
great for your body to control– Frost bite: Sensors are
destroyed– Paralysis: Messages from
brain can’t reach target– Can lead to death
Beck Weathers, thought to be dead, survived a night exposed to Mt. Everest cold.
Homeostasis disruption
Diabetes: inability to control blood sugar
• Normally– Glucose in blood rises after
meals– Pancreas releases insulin– Cells remove the glucose
• Type 1– Immune system destroys
pancreas cells– Pancreas unable to make
insulin– Blood pH decreases as glucose
builds up• Type 2
– Pancreas does not make enough insulin
– Blood pH decreases as glucose builds up
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Review1) Define homeostasis.2) Name and describe the four parts of the “control system.”3) What is negative feedback?4) What is positive feedback?5) Is the following example positive or negative feedback?
During heavy exercise your body loses water when you sweat. As a result of water loss, your body redirects the remaining water inside your body to vital parts of your body to replenish these vital organs.
6) What is diabetes?7) How does Type I and Type II diabetes differ?
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