Download Endocrine System

CHAPTER 45
CHEMICAL SIGNALS IN ANIMALS
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The endocrine system and the nervous system are
structurally, chemically, and functionally related
Why have a hormonal/endocrine system?
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• Homeostasis regulation of body
functions - keeps
body “ON
TRACK”
• Endocrine glands:
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Ductless glands, release
hormones into
BLOODSTREAM
• Exocrine glands:
Glands with ducts, release
enzymes into a
lumen/cavity;
Ex. salivary glands
• Paracrine secretions:
Local regulators
Local regulators affect neighboring target
cells- Paracrine secretions
• Growth factors: proteins and polypeptides that
stimulate cell division
• Nitric oxide (NO)- neurotransmitter, it kills bacteria
and cancer cells, it dilates the walls of blood vessels
(Viagra!!!)
• Prostaglandins secreted by the placenta stimulate
uterine contractions during childbirth; important in
inflammatory response
• Hormones are chemical
signals.
 The endocrine system consists
of:
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 Endocrine cells- hormonesecreting cells and
 Endocrine glandshormone-secreting organs.
 Secrete their hormones
into blood stream and
affect target cells
• Specific target cells respond
to specific hormones =
receptors involved and second
messenger system (chp 11).
 Neurosecretory
cells (neurons
that can produce
hormones)
secrete
hormones into
the blood.
 Located in
hypothalamus
Epinephrine - can signal nerves and act as a hormone
Feedback regulation is a feature of both the
endocrine and nervous systems (negative and
positive feedback loops).
•
Negative regulation - hormone
decreases the stimulus causing its
production:
•
Calcium can be stored in bone or
released to cells via blood (like
glycogen-glucose)
•
Blood Calcium level high
(stimulus)
•
Thyroid makes calcitonin
•
Enters blood
•
Calcium goes from blood to bone
•
Calcium level falls (stimulus
decreases)
•
Hormone release causes stimulus
to decrease- negative feedback
Positive feedback loop- Stimulus makes
the hormone to be released, and hormone
release increases stimulus strength
• Sucking of baby (stimulus)
• Hypothalamus makes
Oxytocin
• Enters blood
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•
Smooth muscle contraction
at nipple releasing milk
• Baby sucks more!!
• Positive feedback- not seen
as often as negative feedback
Invertebrates:
Ecdysone- promotes
the development of
adult features.
Neurosecretory cells
in the brain produce
brain hormone (BH),
which regulates the
secretion of ecdysone.
•Juvenile hormone (JH)
promotes the retention of
larval characteristics.
Fig. 45.2
Signal transduction
- Most chemical signals bind to plasma-membrane proteins,
initiating signal transduction pathways like G protein and
phosphorylation cascade (water soluble hormones)
• Signaltransduction
pathways
allow for
small
amounts of
a hormone
to have a
large effect.
Fig.11.16
Signal transduction
Steroid hormones, thyroid hormones, and some local
regulators enter target cells and bind to intracellular
receptors in the cytoplasm. Next they activate
transcription factors - these bind to DNA in the nucleus
and cause mRNA to be produced which in turn produces
proteins (lipid soluble)
Water soluble Hormones:
Lipid soluble Hormones:
Bind to plasma membrane
receptors on target cells
Enter target cells and bind to
intracellular receptors
Examples: Insulin, epinephrine
Examples: estrogen,
progesterone, vitamin D, NO.
Leads to activation of G
proteins, second messengers
(cAMP), protein kinases enzymes that activate various
proteins including some
transcription factors
May lead to changes in DNA
transcription
Final effect - protein activation
or synthesis
Usually, the intracellular
receptor activated by a hormone
is a transcription factor.
Leads to changes in DNA
transcription
Final effect - protein synthesis
Fig. 45.3b
• Different signal-transduction pathways in
different cells can lead to different responses to the
same signal.
Fig. 45.4
CHAPTER 45
CHEMICAL SIGNALS IN ANIMALS
Section C: The Vertebrate Endocrine System
1. The hypothalamus and pituitary integrate many functions of the vertebrate
endocrine system
2. The pineal gland is involved in biorhythms
3. Thyroid hormones function in development, bioenergetics, and homeostasis
4. Parathyroid hormone and calcitonin balance blood calcium
5. Endocrine tissues of the pancreas secrete insulin and glucagon, antagonistic
hormones that regulate blood glucose
6. The adrenal medulla and adrenal cortex help the body manage stress
7. Gonadal steroids regulate growth, development, reproductive cycles, and
sexual behavior
Introduction
 Tropic hormones
- produced by
hypothalamus and
pituitary gland MASTER
GLAND>target other
endocrine
glands and are
important for
chemical
coordination.
• Humans have
nine endocrine
glands.
Fig. 45.5
Hypothalamus Tropic
Hypothalamus
and
Hormones:
pituitary integrate
endocrine
B) Releasingsystem
hormones
•produced
A) Neurosecretory
by
cells of the stimulate
hypothalamus
hypothalamus
the
anterior pituitary
produce hormones-to
(adenohypophysis)
ADH hormones.
and Oxytocin.
secrete
(FSH,
Reach
posterior
TSH,
ACTH)
pituatary gland for
C) Inhibiting hormones
storage
prevent the anterior
pituitary from secreting
hormones.
D) Nontropic Hormones Prolactin, MSH,
Hypothalamus and pituitary integrate
endocrine system
• A) Neurosecretory
cells of the
hypothalamus
produce hormonesADH and Oxytocin.
Reach posterior
pituatary gland for
storage
• Hormones manufactured by the hypothalamus and
released by the posterior pituitary.
• Oxytocin: a peptide.
• Stimulates contraction of the uterus
(birthing/parturition) and mammary glands (for
milk).
• Secretion regulated by the nervous system.
• Antidiuretic hormone (ADH): a peptide (in excretion
chapter 44)
• Promotes retention of water by the kidneys.
• Secretion regulated by water/salt balance.
Pituatary hormones:
Fig. 45.6b
Table 45.1 (continued)
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• Anterior pituitary hormones.
• Growth hormone (GH): a protein.
• Stimulates growth and metabolism.
• Secretion regulated by
hypothalamic hormones.
• Acts directly on tissues or acts via
growth factors.
• Gigantism: excessive GH during
development.
• Acromegaly: excessive GH
production during adulthood.
• Hypopituitary dwarfism: childhood
GH deficiency.
• Thyroid-stimulating hormone (TSH): a
glycoprotein.
• Stimulates thyroid gland.
• Secretion regulated by thyroxine in blood.
• Secretion regulated by hypothalamic hormones.
• Adrenocorticotropic hormone (ACTH): a
peptide
• Stimulates adrenal cortex secretion of
glucocorticoids
• Secretion regulated by glucocorticoids and
hypothalamic hormones.
• Prolactin (PRL): a protein.
• Stimulates milk production and secretion.
• Secretion regulated by hypothalamic hormones.
• Gonadotropins: glyocoproteins.
• Follicle-stimulating hormone (FSH).
• Stimulates production of sperm and ova.
• Secretion regulated by hypothalamic hormones.
• Luteinizing hormone (LH).
• Stimulates ovaries and testes.
• Secretion regulated by hypothalamic hormones.
• Melanocyte-stimulating hormone (MSH): a
peptide.
• May play a role in fat metabolism.
• Endorphins: peptides.
• Inhibit pain perception.
• Effects mimicked by heroin and other opiate
drugs.
2) The pineal gland is a small mass of tissue near the
center of the mammalian brain.
• The pineal gland secretes the hormone,
melatonin, an amine.
• Involved in biological rhythms associated with
reproduction.
• Secretion regulated by light/dark cycles.
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Thyroid gland:
• Produces
thyroxine
hormone
3. Thyroid hormones function in development, bioenergetics, and homeostasis
• The thyroid gland
of mammals consists
of two lobes located
on the ventral surface
of the trachea.
• Triiodothyronine (T3)
and thyroxine (T4): amines.
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• Stimulates and maintain
metabolic processes.
• Secretion regulated by TSH
hormones.
Fig. 45.8
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Fig. 45.9
Thyroid in Amphibians:
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• Thyroid hormone
functions:
• A) metamorphosis in
amphibians
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• B) Bone and brain
development in some other
animals
• C) Homeostasis in humans
- metabolism control
• Hyperthyroidism - Grave’s diseaseeyes protrude
• Palpitations
• Heat intolerance
• Nervousness
• Insomnia
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• Increased bowel movements
• Light or absent menstrual periods
• Fatigue
• Fast heart rate
• Trembling hands
• Weight loss
• Muscle weakness
• Sweating
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• Hypothyroidism
 An insufficient
amount of thyroid
hormones is known as
hypothyroidism.
 Infants: cretinism.
 Adults: weight
gain, lethargy, cold
intolerance.
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 Goiter: often
associated with
iodine deficiency
(no negative
feedback!)
4) Parathyroid- embedded in the surface of the thyroid
gland.
 Parathyroid Hormone and Calcitonin:
Opposite effects- regulate calcium levels
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-Secretion regulated by calcium in blood.
• Parathyroid hormone (PTH), a peptide.
• Raises blood calcium levels.
• Causes osteoclasts to break down bone, releasing Ca2+ into
the blood.
• Stimulates the kidneys to reabsorb Ca2+.
• Stimulates kidneys to convert vitamin D to its active form.
• Hypoparathyoidism: tetany.- convulsive contraction of
muscles
5) 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.
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Fig. 45.10
•Glucagon: a protein secreted
• Insulin: a protein
secreted by beta cells . by alpha cells.
• Lowers blood glucose
levels.
• Stimulates all body
cells (except brain
cells) to take up
glucose from blood.
• Slows glycogen
breakdown.
• Inhibits
gluconeogenesis.
• Secretion regulated by
glucose in blood
(negative feedback).
•Raises blood glucose levels.
• Inhibits cells from
taking up glucose from
the blood
•Stimulates glyogen
breakdown in the liver
and skeletal muscle.
•Stimulates
gluconeogenesis
•Secretion regulated by
glucose in blood (negative
feedback
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• Hypoinsulinism: diabetes mellitus- “honey water”
• Hereditary factors and obesity play a role in its
development.
• High blood sugar levels – sugar excreted in the urine.
• Symptoms: excessive urination and excessive thirst.
• If severe: fat substitutes for glucose as major fuel
source  production of acidic metabolites  life
threatening lowering of blood pH.
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• Type I diabetes mellitus
(insulin-dependent diabetes).
• Autoimmune disorder.
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• Usually appears in childhood.
• Treatment: insulin injections.
• Type II diabetes mellitus (noninsulin-dependent diabetes).
• Usually due to target cells having
a decreased responsiveness to
insulin.
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• Usually occurs after age 40 – risk
increases with age, weight, stress.
• Accounts for over 90% of
diabetes cases.
6) 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.
• The adrenal medulla is the inner portion.
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• Adrenal medulla.
• Developmentally and
functionally related to the
nervous system.
• Epinephrine (adrenaline)
and norepinephrine
(noradrenaline).
• Flight or fight response
• Increased sugar in blood
• Adrenal cortex reacts to stress- especially
long term.
• Secretes corticosteroids
• Glucocorticoids.
• Raises blood glucose level.
• Secretion regulated by ACTH
(negative feedback).
• Abnormally high doses are
administered as medication to suppress
the inflammation response
• Blood routed to skeletal
muscles, heart, brain (and
not skin, digestive organs)
• Mineralocorticoids (example:
aldosterone, which affects salt and water
balance).
• Increased heart rate,
stroke volume, breathing,
dialtion of bronchioles…
• Promotes reabsorption of Na+ and
excretion of K+ in kidneys.
• Secretion regulated by K+ in blood.
Fig. 45.14
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• A third group of corticosteriods are sex
hormones.
• Androgens secreted by the adrenal cortex may
account for the female sex drive.
• The adrenal cortex also secretes small amounts of
estrogens and progesterone.
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7. Gonadal steroids regulate growth,
development, reproductive cycles, and
sexual behavior
• Testes.
• Androgens (example: testosterone): steroids.
• Supports sperm formation.
• Promote development and maintenance of male
sex characteristics.
• Secretion regulated by FSH and LH.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Ovaries secrete estrogens and progesterone.
• Estrogens: steroids.
• Stimulate uterine lining growth.
• Promote development and maintenance of female sex
characteristics.
• Secretion regulated by FSH and LH.
• Progestins (example: progesterone): steroids.
• Promotes uterine lining growth.
• Secretion regulated by FSH and LH.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings