THE ENDOCRINE SYSTEM AND
HORMONES
Biology GCSE Revision Booklet
, What is a hormone?
A hormone is a chemical molecule and messenger that is secreted into the bloodstream by an
endocrine gland, binding to target cells to perform a specific function.
What is homeostasis?
Homeostasis maintaining a constant state within an internal environment of the body in response
to a change, e.g. ADH controlling water content or insulin controlling blood glucose levels.
Negative Feedback
Negative feedback is the process where a change in a condition from a set level causes a series of
actions that return the condition to the set level. It is how the body keeps conditions within it
constant at the optimum level (homeostasis).
Thermoregulation
Stimulus -> CNS -> Effector -> Response
Vasoconstriction – too cold – reduced blood flow, muscles contract, hairs on skin erect to trap heat
Vasodilation – too hot – increased blood flow as vessels dilate, muscles relax, hairs lay flat, sweat
glands release sweat which evaporates. This uses energy, therefore decreases body temperature.
HORMONES
Biology GCSE Revision Booklet
, What is a hormone?
A hormone is a chemical molecule and messenger that is secreted into the bloodstream by an
endocrine gland, binding to target cells to perform a specific function.
What is homeostasis?
Homeostasis maintaining a constant state within an internal environment of the body in response
to a change, e.g. ADH controlling water content or insulin controlling blood glucose levels.
Negative Feedback
Negative feedback is the process where a change in a condition from a set level causes a series of
actions that return the condition to the set level. It is how the body keeps conditions within it
constant at the optimum level (homeostasis).
Thermoregulation
Stimulus -> CNS -> Effector -> Response
Vasoconstriction – too cold – reduced blood flow, muscles contract, hairs on skin erect to trap heat
Vasodilation – too hot – increased blood flow as vessels dilate, muscles relax, hairs lay flat, sweat
glands release sweat which evaporates. This uses energy, therefore decreases body temperature.
