Homeostasis

• Defined: The maintenance of a constant internal environment

• Importance: Body processes work best in specific conditions

Homeostasis is like your home’s thermostat

Thermostat’s set point is 75ºF

Inside temperature =

heat

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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, causes foot to

move

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Negative Feedback Loops• Counter-acts any change

that moves conditions away from a set point– REVERSES change

– 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– Hypothalamus 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 • Defined: 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?