Transcript Homeostasis of the body - Ms Kim`s Biology Class

Homeostasis
What is homeostasis?
 Process that occurs in all living
things
 All organ systems work
together to achieve
homeostasis
 Ability of an organism to maintain
its internal environment, despite
changes to its internal or external
environment
http://en.wikipedia.org/wiki/File:Tightrope_artist_Cologne_1.jpg
Life Sciences-HHMI Outreach. Copyright
2009 President and Fellows of Harvard
College.
Definition of Homeostasis:
The maintenance of a
constant internal
environment in the
body is called
Homeostasis
What is Homeostasis?
 What do animals need to keep constant?
 Body cells work best if they have the correct
 Temperature
 Osmoregulation- Water balance
 Blood Pressure
 Blood pH level
 Glucose levels
 Oxygen and Carbon Dioxide Levels
 Your body has mechanisms to keep the cells in a constant
environment.
How does homeostasis work?
 Feedback pathways
 A cellular relay race!
 Specific organs and
structures must
communicate with each
other in response to
changes in the body
 Keeps levels of certain
processes within a normal
range
http://en.wikipedia.org/wiki/File:Southern_12_stage-02_1988.jpg
Life Sciences-HHMI Outreach. Copyright
2009 President and Fellows of Harvard
College.
Pathways
 Negative feedback – a stimulus changes some
condition and it triggers a response that reverses
the change. (stops the change)
 Necessary for homeostasis
 An example of negative feedback is your home’s
thermostat
 Positive feedback - the original stimulus initiates a
chain of events that intensify change from an
original condition. (increases change)
 Positive feedback usually moves away from
homeostasis.
 An example of positive feedback is blood clotting.
NEGATIVE FEEDBACK
 Temperature regulation, and water and sunlight regulation in plants are all
examples of negative feedback mechanisms.
 Processes in which an initial change will bring about an additional change
in the opposite direction.
POSITIVE FEEDBACK
 A positive feedback is a process in which an initial change will bring
about an additional change in the same direction.
 An example of a simple positive feedback in everyday life is the
growth of an interest-earning savings account. As interest is accrued
the principal will begin to grow (assuming money is not withdrawn).
As the principal grows, even more interest will be accrued,
quickening the rate of principal growth.
 A good example of a positive feedback system is child birth. 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 goes on until the baby is born.
The birth ends the release of oxytocin and ends the positive feedback
mechanism.

Negative Feedback Loop Example:
Holding
breath,
CO2 levels ri
O2 / CO2 level
returns to normal
Control system
forces exhale,
inhale
Positive feedback increases change
Example: Torn blood vessel stimulates release of clotting factors.
Once a vessel is damaged, platelets start to cling to the injured site and release chemicals that
attract more platelets. The platelets continue to pile up and release chemicals until a clot is
formed.
platelets
blood vessel
fibrin
clot
white blood cell
red blood cell
– growth hormones stimulate cell division
Controlling body temperature
 All mammals maintain a constant body temperature.
 Human beings have a body temperature of about 37ºC.
 E.g. If your body is in a hot environment your body temperature
is 37ºC
 If your body is in a cold environment your body temperature is
still 37ºC
What mechanisms are there to cool the
body down?
1. Sweating

When your body is hot, sweat glands are stimulated to
release sweat.

The liquid sweat turns into a gas (it evaporates)

To do this, it needs heat.

It gets that heat from your skin.

As your skin loses heat, it cools down.
Sweating
The
skin
What mechanisms are there to cool the
body down?
2.



Vasodilation
Your blood carries most of the heat energy around
your body.
There are capillaries underneath your skin that can
be filled with blood if you get too hot.
This brings the blood closer to the surface of the skin
so more heat can be lost.
 This is why you look red when you are hot!
This means more heat is lost from the surface of the skin
If the temperature
rises, the blood
vessel dilates (gets
bigger).
What mechanisms are there to warm
the body up?
1.
Vasoconstriction

This is the opposite of vasodilation
The capillaries underneath your skin get
constricted (shut off).
This takes the blood away from the surface
of the skin so less heat can be lost.


This means less heat is lost from the surface of the skin
If the temperature
falls, the blood
vessel constricts
(gets shut off).
What mechanisms are there to warm
the body up?
2.
Piloerection

This is when the hairs on your skin “stand
up” .
It is sometimes called “goose bumps” or
“chicken skin”!
The hairs trap a layer of air next to the skin
which is then warmed by the body heat
The air becomes an insulating layer.



Temperature Regulation in Humans
 To keep cool:
 Sweating
 Vasodilation
 To keep warm:
 Vasoconstriction
 Piloerection
 Involuntary Muscle Contraction (Shivering)
Homeostasis in Plants
 What do you think plants need to keep constant?
 Water
 Sunlight
 CO2
 Control of water levels in the plant is important to the survival of the
plant.
 This is achieved by a number of methods:
 Waxy cuticle on leaves
 Storage of water
 Opening and closing of stomates
Function of Stomata
Guard Cells
•What process involves using
H2O CO2 and H2O releasing O2 as a
waste product?
What
goes O2
out?
What
goes
in?
Stoma
•Photosynthesis
CO2 •What is the plant using this
process to make?
Stoma Open
Stoma Closed
•Carbohydrates-glucose
•If the plant needs water for
photosynthesis, why is water
coming out of the stoma?
Function of Guard Cells
Guard
Cells
•These stomata
(leaf
openings)
allow water and O2 out of the
leaf.
Guard Cells
•Why would the plant close
stomata with guard cells?
•Prevent excess water loss
through transpiration. (conserve
water)
Stoma Open
•So what is the point of having
stomata?
•Allow gas exchange for
photosynthesis and control water
loss
Stoma Closed
Homeostasis in Plants
 The opening and closing of the stomata maintains water
balance in the plant and thus maintains homeostasis.
 Stems bend towards sunlight to maintain the amount of
photosynthesis.