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