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Endocrine System
Mr. Crabtree
7th Grade Pre-AP Science
Barnett Junior High
Principal characteristics of the
endocrine system
 Made up of endocrine glands that
release chemical messengers called
HORMONES right into the bloodstream
 Allow for the maintenance of the internal
environment in the body, or internal
homeostasis
 Allow the regulation of growth and
development of an organism.
Functions of Endocrine Glands

The endocrine glands include the hypothalamus, pituitary, thyroid, parathyroid,
adrenal, thymus, and pancreas.
Functions of Endocrine Glands
 The ovaries in females and testes in
males are also endocrine glands.
Functions of Endocrine Glands
The pituitary gland communicates with the hypothalamus to
control many body activities.
What Are Hormones?
Hormones are chemical substances created by the
body that control numerous body functions. They
actually act as "messengers" to coordinate functions of
various body parts. Most hormones are proteins
consisting of amino acid chains. Functions controlled
by hormones include:
•activities of entire organs
•growth and development
•Reproduction
•sexual characteristics
•usage and storage of energy
•levels of fluid, salt and sugar in the blood
Endocrine Glands are found
throughout the body
Hypothalamus and
Pituitary are in the
brain
Parathyroids are in the
neck and sit on the
Thyroid
Adrenals sit on the
kidneys
Pancreas is in the
abdomen
Testes are in the scrotum
and Ovaries are in the
hip area
Endocrine system maintains
HOMEOSTASIS
The word homeostasis means “the
maintenance of stable internal conditions in
an organism”.
Example: Blood sugar is too high, and the
pancreas makes more insulin to reduce the
level of insulin. Blood sugar goes down.
When it is low enough, the production
ceases. Insulin will be produced again when
blood sugar again increases.
Negative Feedback
Through negative
feedback, when the
amount of a
particular hormone
in the blood reaches
a certain level, the
endocrine system
sends signals that
stop the release of
that hormone.
The Nervous System is different from
the Endocrine System
The nervous system exerts pointto-point control through nerves,
similar to sending messages by
conventional telephone. Nervous
control is electrical in nature and
fast.
Hormones travel via the
bloodstream to target cells
The endocrine system broadcasts its
hormonal messages to essentially all
cells by secretion into blood and fluid
that surrounds cells. Like a radio
broadcast, it requires a receiver to get
the message - in the case of endocrine
messages, cells must bear a receptor
for the hormone being broadcast in
order to respond.
A cell is a target because is has a specific
receptor for the hormone
Most hormones circulate in blood, coming into contact with
essentially all cells. However, a given hormone usually affects
only a limited number of cells, which are called target cells. A
target cell responds to a hormone because it bears receptors for
the hormone.