28.1 Levels of Organization
Keystone Anchor
•BIO.A.4.2 Explain mechanisms that permit
organisms to maintain biological balance
between their internal and external
environments.
In other words - _______________________________________________
______________________________________________________________
______________________________________________________________
•BIO.A.4.2.1 Explain how organisms maintain
homeostasis (e.g., thermoregulation, water
regulation, oxygen regulation).
In other words - _______________________________________________
______________________________________________________________
______________________________________________________________
28.1 Levels of Organization
KEY CONCEPT
Homeostasis - regulation and maintenance of a
CONSTANT environment in the body
The term ‘homeostasis’ is derived from two Greek
words; Homeo which means ‘unchanging’ and
Stasis which means ‘standing’
It is an organism’s
internal environment
which ‘stays the
same’
28.1 Levels of Organization
Type 1
Think about this person’s body, describe the
factors that need to remain in homeostasis.
28.1 Levels of Organization
• Control systems in the body.
– Sensors -gather data and detect changes
– Control center - receives data, sends messages,
usually the brain
-Communication system - delivers messages in
form of nerve impulses and hormones to target organs,
tissues
– Targets – organ, tissue or cell that responds to
change
28.1 Levels of Organization
Negative feedback loops are necessary for homeostasis.
• Feedback compares current conditions to set ranges.
• Negative feedback- counteracts change.
• Reverses any change and returns body to set point
Negative Feedback Loop
*
Holding breath, CO2
levels rise,
O2 / CO2 level returns to
normal
Keep athlete running
Control system forces
exhale, inhale
28.1 Levels of Organization
KEY CONCEPT
Systems interact to maintain homeostasis.
28.1 Levels of Organization
Each organ system affects other organ systems.
• Organ systems must also work together to keep the
organism healthy.
There is no specific organ which controls
homeostasis.
The skin, kidneys, liver, endocrine system,
nervous system and sensory system all
play a part in maintaining the internal
environment within narrow limits.
The hypothalamus is involved
to a degree in each of these regulations
28.1 Levels of Organization
Type I
Describe how this picture of an automotive
race team is similar to the systems of a body.
28.1 Levels of Organization
• Body cells work best if they have the correct
• Temperature
• Glucose concentration, (sugar)
• Water levels
• Homeostasis involves keeping the internal environment
within set ranges
28.1 Levels of Organization
Organs and involved:
• Water - kidneys :
skin
• regulate water & mineral salts
concentration
tissue
cells
• Thermoregulation –skin and muscles :
• regulate body temperature
• Glucose - liver & pancreas :
• regulate blood glucose level
kidney
liver
blood
+
pancreas
28.1 Levels of Organization
Thermoregulation – process of
maintaining a steady body temperature
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.
28.1 Levels of Organization
Thermoregulation – process of maintaining a steady body
temperature
Shivering
• Hypothalamus signals skin and muscular, respiratory,
and circulatory systems
• Blood vessels constrict to reduce blood flow to prevent
loss of heat
• Muscles contract around pores
• Muscles contract causing shivering
• Thyroid releases hormones that increase
metabolism
28.1 Levels of Organization
Controlling Glucose levels
• Your cells also need an exact level of glucose in the blood.
• Excess glucose gets turned into glycogen in the liver
• This is regulated by 2 hormones (chemicals) from the pancreas called
Insulin and Glucagon
• In this way, the concentration of glucose in the blood is kept within narrow limits
28.1 Levels of Organization
The glucose concentration in the
blood is controlled by the pancreas
The pancreas contains cells which
produce digestive enzymes but it also
produces the hormones insulin and
glucagon
If the glucose concentration rises, the
pancreas releases insulin
If the glucose concentration falls, the
pancreas releases glucagon
12
28.1 Levels of Organization
Insulin stimulates the liver and
muscles to remove excess
glucose from the blood and
store it as glycogen
Glucagon stimulates the
liver to convert its stored
glycogen into glucose which
is then released into the
bloodstream
In this way, the concentration of
glucose in the blood is kept
within narrow limits
28.1 Levels of Organization
Water Regulation
• After having a very salty meal
 produce
concentrated urine to remove
excess salts in solution form
 extra water is needed to be excreted
along with the excess salts
 sensation of thirst (drink more water to
compensate for the water loss)
28.1 Levels of Organization
Water Regulation
• The amount of water in the blood must be kept more or less the
same all the time to avoid cell damage as a result of osmosis.
• There has to be a balance between the amount of water gained (from
your diet though drinks and food and the water produced by cellular
respiration) and the amount of water lost by the body (in sweating,
evaporation, feces and urine).
• This is achieved by the action of the hormone ADH (anti-diuretic
hormone).
28.1 Levels of Organization
Water Regulation
• Part of the brain, the hypothalamus, detects that there is
not enough water in the blood. The hypothalamus sends
a message to the pituitary gland which releases ADH.
• This travels in the blood to your kidneys and as a result
you make a smaller volume of more concentrated urine.
The level of water in your blood increases until it is back
to normal.
• If the level of water in your blood goes up the
hypothalamus detects the change and sends a message
to the pituitary. The release of ADH into the blood is
slowed down or even stopped. Without ADH the kidneys
will not save as much water and you produce large
volumes of dilute urine.
• This is an example of negative feedback.
28.1 Levels of Organization
• There are 11 major organ systems in the human body.
28.1 Levels of Organization
TYPE I
• Name 3 systems that help maintain homeostasis and describe how
they work to maintain homeostasis.
• 1.
• 2.
• 3.