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Regulatory systems
• There are two basic types of regulatory systems
• Endocrine system
• Nervous system
These two system are structurally, chemically and functionally
related. Many nervous systems have neurosecretory cells that
secrete hormones which act on some region of the organism.
Several chemicals serve both as hormones and as signals in
the nervous system. There are also several regulatory
processes that overlap between the endocrine and the nervous
systems. Also feed back mechanisms, both positive and
negative, operate in both the endocrine and the nervous
system
Figure 45.1 An example of how feedback regulation
maintains homeostasis
Neurosecretory cells
in brain produce brain
hormone (BH)
Figure 45.2 Hormonal regulation of insect
development
BH signals its main target,
the prothoracic gland, to
produce ecdysone
Ecdysone secretion is
episodic with each release
stimulating the molt
Low
high
Juvenile hormone (JH) is secreted by the corpus allatum and
determines the results of the molt. High concentration results in a
larvae produced by the molt and low levels stimulate metamorphosis
Chemical Signals and Their Modes
of Action
1. A variety of local regulators affect neighboring target cells
2. Most chemical signals bind to plasma-membrane proteins, initiating signal
transduction pathways
3. Steroid hormones, thyroid hormones, and some local regulators enter target
cells and bind to intracellular receptors
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A variety of local regulators affect
neighboring target cells
• Growth factors: proteins and polypeptides that stimulate
cell proliferation Example: nerve growth factor (NGF) affects certain
embryonic cells, developing white blood cells, and other kinds of cells
• Nitric oxide (NO)
–
–
–
–
Though a gas, NO is an important local regulator.
When secreted by neurons, it acts as a neurotransmitter.
When secreted by white blood cells, it kills bacteria and cancer cells.
And when secreted by endothelial cells, it dilates the walls of blood
vessels.
• Prostaglandins (PGs): modified fatty acids.
– PGs secreted by the placenta stimulate uterine contractions during
childbirth.
– Other PGs play a role in inflammation and the blood flow to the
lungs.
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Most chemical signals bind to plasma membrane
proteins, initiating signal-transduction pathways.
Fig. 45.3a
Different signal-transduction pathways in different cells can lead to different
responses to the same signal. In this case it is the neurotransmitter,
acetylcholine
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Fig. 45.4
Steroid hormones, thyroid hormones, and
some local regulators enter target cells and
bind to intracellular receptors
• Examples: estrogen, progesterone, vitamin D, NO.
– Usually, the intracellular receptor activated by a hormone is a
transcription factor. (shown in b below)
Fig. 45.3b
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• Humans have
nine endocrine
glands.
The hypothalamus and pituitary integrate many
functions of the vertebrate endocrine system
• The hypothalamus integrates endocrine and nervous
function.
– Neurosecretory cells of the hypothalamus produce
hormones.
• Releasing hormones stimulate the anterior pituitary
(adenohypophysis) to secrete hormones.
• Inhibiting hormones prevent the anterior pituitary
from secreting hormones.
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The anterior pituitary gland is derived from a fold of tissue on the
roof of the embryonic mouth. Neurosecretory cells of the
hypothalamus exert control over the anterior pituitary gland
Source of releasing
and inhibiting hormones
Fig. 45.6b
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 The posterior
pituitary
(neurohypophysis)
is derived from
brain tissue
and stores and
secretes
hormones
produced
by the
hypothalamus.
Fig. 45.6a
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• Regulation of blood osmolarity is maintained by hormonal
control of the kidney by negative feedback circuits.
One hormone important in regulating water balance is antidiuretic
hormone (ADH). ADH is produced in hypothalamus of the brain and stored
in and released from the pituitary gland, which lies just below the
hypothalamus. Osmoreceptor cells in the hypothalamus monitor the
osmolarity of the blood.
• When blood osmolarity rises
above a set point of 300
mosm/L, more ADH is released
into the blood stream and
reaches the kidney. The
epithelium of the distal tubules
and collecting ducts become
more permeable to water. This
amplifies water reabsorption,
reduces urine volume and
helps prevent further increase
of blood osmolarity above the
set point.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The next two slides are given for added
discussion but will not be examined in
examinations in this course.
Endocrine tissues of the pancreas secrete insulin and
glucagon, antagonistic hormones that regulate blood
glucose
• The pancreas has both endocrine and exocrine functions.
– Exocrine function: secretion of bicarbonate ions and digestive
enzymes.
– Endocrine function: insulin and glucagon secreted by islets of
Langerhans.
– Insulin: a protein secreted by beta cells.
• Lowers blood glucose levels.
– Stimulates all body cells (except brain cells) to take up
glucose.
– Slows glycogenolysis.
– Inhibits gluconeogenesis.
• Secretion regulated by glucose in blood (negative feedback).
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Fig. 45.10
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The adrenal medulla and adrenal cortex help the body manage stress
•
The adrenal glands are located adjacent to the kidneys.The adrenal
cortex is the outer portion and secretes corticosteroids and is regulated
by the nervous system in response to stress..The adrenal medulla is the
inner portion and produces epinephrine (adrenaline) and norepinephrine
(noradrenaline) and also regulated by the nervous system.
Fig. 45.14
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• Epinephrine (adrenaline) and
norepinephrine (noradrenaline).
• Catecholamines: amines synthesized from tyrosine.
• Secretion regulated by the nervous system in
response to stress.
• Raises blood glucose level and blood fatty acid level.
• Increase metabolic activities.
– Increases heart rate and stroke volume and dilates bronchioles.
• Shunts blood away from skin, digestive organs, and
kidneys, and increases blood flow to heart, brain, and
skeletal muscle.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings