Endocrine System -Training Handout
Karen L. Lancour
National Rules Committee Chairman – Life Science
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Basic anatomy and physiology of the human endocrine system
Definition of hormones
Types of endocrine glands and their hormonal effects
Endocrine related problems
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ENDOCRINE SYSTEM AND HOMEOSTASIS
Homeostasis
Feedback Mechanisms
Stimulus
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change in homeostatic environment
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signal sent to CNS
Response
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signal sent from CNS
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produce effect
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body returns to
homeostasis
Type of Glands
Exocrine gland
Ducts
Lumen and surfaces
Endocrine gland
Chemical messengers
Blood stream
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Hormones – produced by endocrine glands
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specific chemical compound
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produced by a specific tissue of the body
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released in the body fluids
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carried to a distant target tissue
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affects a pre-existing mechanism
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effective is small amounts.
Chemical messengers
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Secreted by endocrine gland
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Specific to target
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Activate cellular change
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Of 4 different chemical types
Mechanisms of Hormone Action
 Endocrine Glands - secrete chemical (hormones) into blood
 Hormones - communicate and control slower than nerves
 Hormones - act on Target cells
Classes of Hormones:
peptides – short chains of amino acids (most hormones)
pituitary, parathyroid, heart, stomach, liver & kidneys
amines - derived from tyrosine and secreted by thyroid and adrenal cortex
steroids - lipids derived from cholesterol secreted by the gonads, adrenal cortex, and placenta
eicosanoid - produced from 20-carbon fatty acid, arachadonic acid, produced in all cells except
RBCs -Prostaglandins and leukotrienes
Peptide/Protein
 Hydrophilic
 Large
 Can't fit through membrane
 Second messenger mechanism of action
 Most common hormone
 translated, packaged, & sent
 Hydrophilic/Lipophobic
 Bind surface receptors at target
 Binding mediates signal transduction/2nd messenger system
 Example: Insulin
Amine
 Synthesized from a single amino acid
 Melatonin from tryptophan
 Thyroid hormone from tyrosine
 Catecholamines (EPI, DA) from tyrosine
Eicosanoid
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Produced from 20-carbon fatty acid, arachadonic acid
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Produced in all cells except RBCs
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2nd messenger
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Prostaglandins and leukotrienes
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inflammation
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Steroid Hormones
 Small
 Hydrophobic/Lipophilic
 Travel in blood w/carrier
 Cytoplasmic or nuclear receptors
 change protein synthesis
 Example: estradiol
Two Mechanisms of Hormone Operation – Hormone plus receptor
Note the difference in action between the Steroid hormones and the other hormones
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Mechanism of Hormone Action:
Peptides and Amines – non-steroid water soluble
Protein hormones (1st messengers) - bind to receptor on target cell triggering 2nd messenger to affect cell’s
activity
st
 hormone (1 messenger) does not enter the cell
 bind to receptor on the plasma membrane receptors
 hormone-receptor complex activates G protein
nd
 generates chemical signal (2 messenger) – most common is cAMP and IP3
nd
 2 messenger chemical signal activates other intracellular chemicals to produce response in target cell
 responses may be phosporylation, activation of enzymes
release of calcium ions into cytosol from ER, turn on
transcription factor CREB for protein production.
Steroid hormones – fat-soluble hormones
bind to receptors within target cell and influence cell activity by acting on specific genes
 hormone diffuses freely into cell where cytoplasmic and/ or nuclear proteins serve as receptors
 hormone binds to receptor (hormone-receptor complex)
 complex bonds to steroid response element (sections of DNA receptive to the hormone-receptor
complex
 hormone-receptor complex acts as transcription factor
to turn target genes “on” or “off”
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Neurosecretory Cells
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Specialized neurons
Synthesize and secrete hormones
Extend from HYPOTHALAMUS to
POSTERIOR PITUITARY
Neurosecretory cells in Hypothalamus
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Nuclei synthesize and secrete hormones
Neuronal connection to POSTERIOR
pituitary
Antidiuretic Hormone (ADH), Oxytocin
Hypothalamus
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Connection to pituitary
Neuronal to POSTERIOR PITUITARY
Endocrine to ANTERIOR PITUITARY
RH = Pituitary releasing hormones
RIH = Pituitary release inhibiting
hormones
Secretes regulatory homones
"Directs" pituitary
Release Inhibiting Hormones
Somatostatin
Prolactin release inhibiting hormone-PIH
Releasing Hormones
Thyrotropin releasing hormone-TRH
Growth hormone releasing hormone-GHRH
STIMULUS
Hypothalamus
Releasing Hormone
(Release-Inhibiting Hormone)
Pituitary
Stimulating
Hormone
Gland
Hormone
Target
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Types of Feedback
Positive Feedback
 Not common
 Classic example:
 Action of OXYTOCIN on uterine muscle during birth.
 Baby pushes on cervix
 Nervous signal to Hypothalamus
 Hypothal. manufactures OXY
 OXY transported to POSTERIOR PITUITARY & released
 OXY stimulates uterine contraction
 Loop stops when baby leaves birth canal
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Negative Feedback
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Most common control mechanism
Level of hormone in blood or body’s
return to homeostasis shuts off loop at
hypothalamus and pituitary
Endocrine Disorders:
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Hyposecretion disorders are caused by too little hormone – they can be treated by addition of the
hormone
Hypersecretion disorders are caused by too much hormone – these are much harder to treat
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