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7.4: Homeostasis and Cells Key Terms

• Homeostasis

• Specialized Cells

• Tissue

• Organ

• Organ System

• Receptors

Key Concepts

• How do individual cells maintain homeostasis?

• How do multiple cells work together to maintain homeostasis?

A little demo to start off the day…

• Everyone stand up.

• Now balance on one foot until I tell you to stop.

• While you are waiting for me to tell you to stop, take turns

describing to your neighbor what you are experiencing.

Demo Wrap-up Questions

• Describe what happened to your body

while balancing on your leg?

• Did you notice anything?

• Did it get more difficult

as time went on?

• What did you want to

do?

What is Homeostasis?

• Definition:– Process by which the body

maintains a stable internal environment

– Example: humans will sweat when they are too hot and shiver when they are too cold

• All living organisms must maintain homeostasis

How do you think the bacteria live in this?

• Unicellular organisms tend to be self-sufficient in living on own

• Multicellular organisms are interdependent– Their cells tend to be

specialized with specific task to maintain homeostasis

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How would the function of the cells in the digestive tract vary based off the pictures above?

Levels of Organization

• Specialized cells � tissue � organ �

organ system

• Tissue – group of similar cells performing the same function

• Organ – group of tissue working together

• Organ system- group of organs working together to perform same function

Small

BIG

• Levels of

organization allow the body’s cells to

divide labor among

individual cells which allows for

homeostasis to

take place

Cellular Communication

• Cells communicate

with each other via chemical signals

– These can speed up

or slow down activities inside cell

Transportation of Message

• Some cells form

cellular junctions between

neighboring cells

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• Some cells allow

small molecules carrying message

to directly enter

cell using receptors

• Example: heart beat

– Ions carry electrical signal from cell to cell through special junctions in heart

– Millions of heart muscle cells then contract in a single heart beat

– Other junctions hold cells together so muscle doesn’t tear

Organ Systems Example of Homeostasis

• Nervous System is the

master controller in maintaining

homeostasis

– But it does not work alone… the Endocrine

System helps

How do they control homeostasis?

• The nervous system sends out rapid

electrical impulses to the body

• The endocrine

system sends hormones through the

blood at a slower more steady pace

How is homeostasis maintained?

• Feedback Loops

– When brain receives message from body about internal change, it works to restore

system to normal state

– Two types of feedback loops

• Negative

• Positive

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3 Components of a feedback system:

• Receptor:

detects a change in some variable

of the animal’s

internal environment

(e.g. body

temperature)

3 Components of a feedback system:

• Control center:

processes information it

receives from

the receptor (brain,

hypothalamus)

3 Components of a feedback system:

• Effector: receives

a message from the control center

and responds

appropriately (muscles �

shivering,

goosebumps)

NEGATIVE FEEDBACK

• Example: body temperature (needs to stay

around 37°C)

rise in � brain � message to � body temp.

temp. “thermostat” sweat glands lowers

to produce

sweat

**Negative feedback maintains HOMEOSTASIS!

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POSITIVE FEEDBACK

• Example: childbirth

(body needs

to achieve a heightened

state of exertion…

LABOR!)

pressure � uterine � more � more

of baby’s contractions pressure contractions…..

head