Mechanisms of Homeostasis

Homeostasis is like your home’s thermostat

Thermostat’s set point is 75ºF

Inside temperature =

heat

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• Defined: Process where the body maintains a constant internal environment

• Importance: Internal reactions & enzymes work best in specific conditions

• Control systems adjust to internal/external changes

• Changes controlled: pH, temp, fluids

Control Systems• Sensors (aka: receptors)

– Gather information about the body and environment

– Ex: skin senses pressure• Communication Center

– Messages sent throughout the body to respond

– Ex: Impulse travel through your nerves

• Control Center– Receives information from the

sensors– Ex: Brain interprets the impulse

• Targets– Body part that changes its activity– Ex: Muscles in foot stretch/contract

abruptly

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Negative Feedback Loops• Regulates most of

the body• 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• Regulates most of

the body• 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

Negative Feedback Loop: Breathing

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

Ask yourself…If this was negative feedback, what would happen next?

Negative feedback would reverse and stop the contractions. But if the contractions stopped, would the baby be delivered?

So how will the body respond to the contractions if it’s positive feedback?

Working Together

• Thermoregulation: Maintenance of body temperature– Skin: sensors detect cold– Nervous system: electrical impulse sent to brain– Endocrine system: releases hormones into blood stream– Muscles: Hormones cause shivering

• Some disruptions temporary– Infections, fever, sore

throats, muscle soreness

• Some disruptions too great for your body to control– Frost bite: Sensors are

destroyed– Paralysis: Messages

from brain doesn’t reach target

Beck Weathers, thought to be dead, survived a night exposed to Mt. Everest cold.

Homeostasis disruption

Diabetes & Homeostasis

• 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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Kobe Kuiz1) 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?