Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Blood Glucose
The level of glucose in the bloodstream fluctuates as food is
eaten or energy is expended. When the levels of blood glucose
rise, cells in the pancreas known as beta cells detect the
increase and release the hormone insulin. Insulin functions to
facilitate the uptake of glucose into the cells of the body where
it can be metabolized. Insulin also signals the liver to convert
glucose into the storage molecule glycogen. All of these result
in a decrease in the levels of glucose in the blood. If the blood
glucose levels fall to a dangerously low level, cells in the
pancreas known as alpha cells detect the decrease and release
the hormone glucagon. Glucagon functions to signal the liver
to convert glycogen into glucose and release it into the
bloodstream.
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Blood Glucose
Levels of blood glucose
increase
Change (Cause) Result (Effect)
Levels of blood glucose
decrease
Change (Cause) Result (Effect)
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Water Levels
The body works to ensure that there is a balance between the
amount of water taken in and the amount of water lost. The
amount of water in the blood is sensed by receptors in the
hypothalamus of the brain, known as osmoreceptors. If the
body is becoming water deficient, the osmoreceptors send a
signal to the pituitary gland to increase the secretion of the
anti-diuretic hormone (ADH). ADH stimulates the kidneys to
retain more water and reduce the amount of urine output. If
there is an excess amount of water in the blood, the
production of ADH is suppressed. This results in less water
being retained by the kidneys and an increase in the volume of
urine produced.
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Body Temperature
Increase in body
temperature
Change (Cause) Result (Effect)
Decrease in body
temperature
Change (Cause) Result (Effect)
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Body Temperature
Humans maintain a relatively constant body temperature in a variety of
conditions. The skin and hypothalamus portion of the brain are
responsible for this phenomenon. Thermoreceptors found on the skin
monitor skin temperature and signal the brain to respond appropriately
to either hot or cold conditions. The body responds to hot conditions
by increasing sweat production and dilating blood vessels under the
surface of the skin to increase blood flow. The increased blood flow
allows heat to be delivered to and lost through the surface of the skin.
The body responds to cold conditions by decreasing sweat production,
triggering the shivering response and constricting blood vessels under
the surface of the skin to decrease blood flow. The decreased blood
flow to the skin redirects heat away from the surface of the skin
towards the internal organs.
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Water Levels
Levels of water in the
blood decrease below
normal levels
Change (Cause) Result (Effect)
Levels of water in the
blood increase above
normal levels
Change (Cause) Result (Effect)
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Blood Pressure
Blood pressure is a measure of the pressure that blood exerts
on the walls of blood vessels as it circulates. An increase in
blood pressure is detected by a receptor known as the
baroreceptor, found in blood vessels. This signals the medulla
of the brain stem to decrease the heart rate. When the heart
rate decreases, blood pressure decreases. If the blood
pressure drops too low, the baroreceptors detect the decrease
and signal the medulla to increase the heart rate.
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Respiration
Increase in the level of
CO2 in the blood
Change (Cause) Result (Effect)
Decrease in the level of
CO2 in the blood
Change (Cause) Result (Effect)
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Respiration
Respiration is controlled by the levels of CO2 in the blood and
is detected by chemoreceptors found in three locations, one in
the medulla in the brain stem and two others near the heart.
When an increase in the level of CO2 is detected, the medulla
signals the diaphragm and the rib muscles to increase the
breathing rate. This in turn results in an intake of O2 and an
expulsion of CO2, decreasing the levels of CO2 in the blood. If
CO2 levels in the blood become too low, the breathing rate is
decreased and CO2 levels in the blood increase.
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Regulation of Blood Pressure
Increase in blood pressure
Change (Cause) Result (Effect)
Decrease in blood
pressure
Change (Cause) Result (Effect)
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Biology Unit 13 Topic 4 Regulation in Animal Systems
Homeostasis Scenarios
RISD Curriculum & Instruction
Maintaining Homeostasis
In Animals
Instructions: Read each scenario and for each change (cause) identified on the
left, record the results (effects) in the order they occur.
Negative Feedback
Positive Feedback