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KEY CONCEPT #5
The endocrine system produces hormones that affect
growth, development, and homeostasis.
Hormones influence a cell’s activities by entering the cell or
binding to its membrane.
• Glands are organs of the endocrine
system.
• Hormones are chemical signals that influence cell’s
activities.
 produced by glands
 travel through the circulatory system
 affects target cells with matching receptors
target cell
hormone
bloodstream
receptor
not a target cell
• There are steroid (lipid) hormones and nonsteroid (protein)
hormones.
 Steroid hormones enter the cell.
 Nonsteroid hormones do not enter the cell.
Steroid hormone
Steroid hormone
diffuses through the
cell membrane
Nonsteroid hormone
binds to receptor on
the cell membrane.
Non-steroid
hormone
receptor
Steroid hormone
binds to a receptor
within the cell.
receptor
nucleus
The hormone and
receptor enter the
nucleus and bind to
DNA
DNA
Steroid hormone
causes DNA to make
proteins.
proteins
Receptor stimulates a
second messenger with
in the cell.
Second messenger
starts a series of
chemical reactions in
the cytoplasm.
Second messenger
reactions activate
enzymes.
second
messenger
Chemical
reactions
activated
enzymes
Endocrine glands secrete hormones that act throughout the
body.
• There are many glands located throughout the body.
HYPOTHALAMUS
PITUITARY
THYROID
THYMUS
ADRENAL GLANDS
PANCREAS
FEMALE GONADS:
OVARIES
MALE GONADS : TESTES
– Hormones travel through the bloodstream to cells with
matching receptors.
The hypothalamus interacts with the nervous
and endocrine systems.
 The hypothalamus is a gland found in the brain.
– a structure of both the nervous and
endocrine systems
– produces releasing hormones,
sent to pituitary gland
• The pituitary gland is found below
the hypothalamus in the brain.
– controls growth and water
levels in blood
– produces releasing hormones
sent throughout the body
 Releasing hormones stimulate other glands to produce
hormones.
– allow glands to communicate with
one another
– are used in temperature regulation
Hormonal imbalances can cause severe
illness.
 Abnormal hormone levels affect homeostasis.
 Hormonal imbalances might be treated with surgery
or medicine.
 Steroids, a pituitary tumor, or some prescription
drugs can make the pituitary overactive and
indirectly cause problems.