Hormones Act on Target Cells
endocrine glands, hormones, hormone
receptors, and target cells.
how steroid hormones act.
how nonsteroid hormones act.
o maintain a steady state, the body must reg-
ulate many parameters, such as heart rate,
breathing, blood glucose, fluid balance, and so
on. The nervous system regulates many of these
on a moment-by-moment basis and is ready to rapidly re-
spond to changes within seconds. Besides the nervous system,
regulates many parameters chemi-
cally. Let’s look at the components of the endocrine system.
The Endocrine System Has
The endocrine system consists of several components (see
Endocrine glands are glands
that secrete a chemical signal
rather than through a duct or
tube. For example, the salivary
gland is an exocrine gland; it
secretes saliva through a duct.
In contrast, the pituitary, thyroid, parathyroid, adrenal,
and pineal glands are endocrine glands because they
secrete chemicals into the bloodstream.
A system of
glands and hormone-
secreting cells that
regulate body func-
tions through chemical
C o m p o n en ts o f th e en d o crin e sy stem • Figure 9.1
This figure shows the major endocrine glands (red), organs that contain endocrine cells (blue), and some
nearby organs for reference (a), and indicates the functional components of the endocrine system (b).
a. Location of endocrine glands
b. How endocrine
Endocrine glands or
(cell activity gets changed