The Endocrine System

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Chapter 17
BIOLOGY
Patterns and Processes of Life

• The Endocrine System

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Figure 17.2

Membrane receptors facilitate the coordination of
gene expression and key developmental events.
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Figure 17.4

The nervous system carries signals between the
brain and the rest of the body at speeds of up to
150 m/sec!
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Figure 17.5

Chemical signaling by hormones (a) Endocrine
hormones are produced by cells of endocrine
glands and transported by the blood to target
cells. (b) Some hormones are released by
neurosecretory cells, which function in both the
nervous and endocrine systems. (c) A few
hormones are secreted over short distances
through tissue fluid.
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Figure 17.7

The mechanism of peptide hormones (1) Peptide
hormones are produced by an endocrine gland and
carried by the blood. (2) Receptors on the
plasma membrane of a target cell bind with the
hormone. The hormone itself does not enter the
cell. (3) An enzyme in the plasma membrane
changes ATP to cyclic AMP (cAMP). The cAMP
molecule is the second messenger, carrying the
hormones signal through the cell. (4) Enzymes
are activated, triggering a series of reactions.
(5) These reactions bring about the changes
controlled by the hormone.
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Figure 17.8

The mechanism of steroid hormones (1) Steroid
hormones are released by endocrine cells and
carried by the blood. (2) Because of their size
and structure, steroid hormones enter the cell.
(3) The hormones enter the nucleus, where they
bind to receptor molecules. The hormone-receptor
complex binds to DNA and regulates gene
expression. (4) If the gene is switched on it
will be transcribed and translated to protein.
(5) The protein made in this way is the effect of
the hormones release.
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Figure 17.10

The hormones controlling insect development (a)
Hormones secreted by the brain and prothoracic
gland Neurosecretory cells in the brain produce
brain hormone (BH), which is stored and released
by a gland just behind the brain. BHs main
target is the prothoracic gland, which produces
molting hormone (MH), also called ecdysone. The
corpus allatum produces juvenile hormone (JH).
(b) Hormones effects on development of Cecropia
moth Development is the result of interactions
between JH and MH. MH is produced to stimulate
growth and molting. When JH concentrations are
high, a molt produces a larger larva. When JH
level drops, the larva molts and becomes a pupa.
At this point, JH production stops and the moth
develops its adult organs and emerges from the
pupa.
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Figure 17.12

The hypothalamus and pituitary control and
coordinate endocrine function.
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Figure 17.13

The anterior pituitary Neurosecretory cells of
the hypothalamus produce releasing and inhibiting
hormones (red dots). These hormones enter
capillaries in the hypothalamus, move through
portal vessels and reach their target cells via a
second capillary system in the anterior lobe of
the pituitary. Endocrine cells in the anterior
pituitary secrete hormones which are carried to
other endocrine glands in the body.
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Figure 17.14

The posterior pituitary Neurosecretory cells of
the hypothalamus are connected directly to the
posterior pituitary. These cells produce ADH and
oxytocin, which are stored in and released by the
posterior pituitary.