hormones and the endocrine system chapter 45 p. 943-963
TRANSCRIPT
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Hormones and the Endocrine System
Chapter 45
p. 943-963
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Hormones: an introduction
Hormone: chemical signal secreted to communicate regulationCarried in blood or hemolymphTarget Cells: specific cells that respond to
hormones Endocrine System: consists of cells &
ductless glands that secrete hormones directly into body fluids
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Endocrine-Nervous System Relationship Both systems have structural, functional, &
chemical similarities Regulate each other through + & - feedback systems Nervous System: rapid messages w/ immediate
response Endocrine System: slower, longer-lasting responses
Neurosecretory Cells: nerve cells of endocrine system that secrete hormones i.e.: Epinephrine: acts as both hormone & nervous
system signal
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Control Pathways
Endocrine control systems include a receptor, a control center, and an effector
4 Types (see Fig 45.2): 1) Simple Endocrine: involves endocrine cells only 2) Simple Neurohormone: involves neurosecretary
cells only 3) Simple Neuroendocrine: involves endocrine &
neurosecretary cells 4) Complex: involves one hormone controlling
another Most are (-) feedback systems
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Classes of Hormones
1) Proteins & Peptides: small polypeptides H2O soluble
2) Amines: derived from amino acids H2O soluble
3) Steroids: lipid w/ 4 C-rings & a functional group attached NOT H2O soluble
All involve reception, signal, and response
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The Signal-Transduction Pathway
1) Reception: signal molecule binds to specific receptor protein A) Plasma Membrane Receptors
i.e. for epinephrine, frog’s camouflage
B) Intracellular Receptors (in nucleus)
2) Signal Transduction: results in response i.e. enzyme activation,
uptake/secretion molecules, etc. Target cells determine the
response
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Intracellular Receptors
Nucleus is target for small, non-polar molecules that pass easily through cell membrane i.e. steroid & thyroid hormones, vit D, NO
Signal is transducted within cell; stimulates/represses transcription of genes i.e. Estrogen: stimulates female bird cells to produce
ovalbumin (egg white protein)
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Chemical Signaling Modes of Action
A) Local Regulators: act on neighboring cells Elicit response much more quickly than hormones 1) target cells take up signal 2) enzymes break down signal (non-target cells) 3) signal is fixed in extracellular matrix (storage) Types: Paracrine & Synaptic
B) Long-Distance: signal travels through blood stream to reach target cell Type: Hormonal
C) Pheromones: act between individuals i.e.: to attract mates
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Types of Local Regulators
1) Growth Factors: peptides/proteins; stimulate cell division, growth, & development i.e.: Nerve Growth Factor: speeds dvlpmt of
embryonic nerve cells, WBC, others 2) Nitric Oxide (NO): gas; many functions,
highly reactive, may be toxic i.e.: neurotransmitter, kills bacteria & cancer cells,
relaxes smooth muscle 3) Prostaglandins (PG): modified FA’s;
important in reproductive functions i.e.: uterine contractions, induces fever, antagonistic
muscle action
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The Vertebrate Endocrine System Hormones may target few
tissues or many Tropic Hormones: target
other endocrine glands & aid in chemical coordination
Some organs outside endocrine have cells that secrete hormones i.e.: stomach, heart, kidney,
placenta Thymus Gland: important
in the immune system
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Endocrine Glands
Chapter 45
p. 948-961
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Hypothalamus/Pituitary Relationship Hypothalamus: contains 2
sets of neurosecretory cells in lower brain that regulate the pituitary Integrates endocrine & nervous
system
Posterior Pituitary “neurohypophysis”: extension of the hypothalamus Stores & secretes hypoth.
hormones
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Hypothalamus/Pituitary Relationship (con’t)
Anterior Pituitary “adenohypophysis”: endocrine cells that make & secrete hormones into blood Develops from embryonic mouth
tissue Controlled by tropic hormones of
the hypothalamus: Releasing Hormones: cause ant.
pit to release hormones Inhibiting Hormones: stop
secretion from ant. pit Portal vessels connect
hypothalamus to anterior pituitary
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Posterior Pituitary Hormones
BOTH are peptides, use simple neurohormone pathway, and are (+) feedback systems1) ADH: acts on kidneys to retain H2O & ↓
urine volume Helps regulate blood osmolarity
2) Oxytocin: induces muscle contractions on birth & milk release during nursing
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Anterior Pituitary Hormones
A) Tropic Hormones: all use complex pathways1) FSH & LH “gonadotropins”: stimulate
activity of ovaries &testes2) TSH: promotes development of thyroid
gland & hormones3) ACTH: stimulates production & secretion of
steroid hormones by adrenal cortex
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Anterior Pituitary Hormones (con’t) B) Nontropic Hormones: all use simple
neuroendocrine pathways 1) Prolactin: variety of effects in different vertebrates
Indicates evolutionary significance 2) MSH: regulates activity of pigment cells & plays
role in fat metabolism 3) Endorphins: produced by neurosecretary cells;
dull pain perception C) Growth Hormone: tropic & nontropic effects
Variety of actions Helps stimulate bone & cartilage growth, may ↑ blood
glucose (oppose insulin) Abnormal production may lead to gigantism or
dwarfism
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Pineal Gland
Near center of brain Contains light-sensitive cells & is
connected to the eye Involved in biorhythms of reproduction
Link between biological clock & activity
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Thyroid Gland
On ventral side of trachea Mostly releases T4 which converts to T3 at target
cell – contain iodine Involved in skeletal & mental development Maintains normal BP, HR, muscle tone,
digestion & reproduction Hyperthyroidism: ↑ thyroid hormones cause ↑ body
temp, sweating, weight loss, ↑ BP Hypothyroidism: ↓ hormones cause infant cretinism,
weight gain, lethargy Goiter: ↓ hormones caused by lack of iron (can not
synthesize T4 & T3)
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Parathyroid
4 glands embedded in thyroid When blood Ca2+ is low, PTH causes:
1) Osteoclasts to decompose bone matrix to release Ca2+
2) Kidneys to reabsorb Ca2+ into blood & activate vit D
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Pancreas
Upper abdominal cavity Both exocrine & endocrine functions Produces bicarbonate & digests enzymes Islets of Langerhans: clusters of endocrine
cells; regulate glucose conc. in blood Alpha: secrete glucagon (↑ [glucose] in blood) Beta: secrete insulin (↓ [glucose] in blood)
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Diabetes
Type I Diabetes Mellitus: “insulin-dependent” or “juvenile onset”Autoimmune disorderDestroys ability to produce insulin
Type II Diabetes Mellitus: “non-insulin dependent” or “adult onset”Caused by heredity or obesityCauses insulin deficiency or ↓ target cell
responsiveness
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Adrenal Glands
Adjacent to the kidneys Adrenal Medulla: central gland
Hypothalamus controls thru nervous system Secretes epinephrine & norepinephrine (↑ blood
glucose) “Fight-or-Flight”
Adrenal Cortex: outer gland Hypothalamus controls thru hormones Secretes glucocorticoids (glucose synthesis) &
mineralocorticoids (NaCl & H2O balance)
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Gonads
Testes (males) & Ovaries (females) Affect growth & development and regulate
reproduction cycles & sexual behavior Controlled by FSH & LH