Endocrine System

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Endocrine System

• Dr. Annette M. Parrott
• GPC
• BIOL1612

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Endo crine Systeminside secrete

• Odd organ system
• Compared to nervous sys. digestive sys.
• Endocrine glands usually not connected
• Considered a system because of functional
  similarity
• Secrete chemical messages called hormones to
  target cells to
  excite

Also skin, heart, GI tract, placenta, kidneys,
adipose tissue
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Principal functions of the endocrine system

• Maintenance of the internal environment in the
  body (maintaining the optimum biochemical
  environment).
• Integration and regulation of growth and
  development.
• Control, maintenance and instigation of sexual
  reproduction and development.

Glands with a sensing and signaling system which
regulates the duration and magnitude of hormone
release via feedback from the target cell.
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Types of hormones

• Hormones are categorized into four structural
  groups, with members of each group having many
  properties in common
• Peptides and proteins (polypeptides)
• Amino acid derivatives
• Steroids (cholesterol based)
• Fatty acid derivatives - Eicosanoids (mostly
  paracrines, i.e. leukotrines, prostaglandins)

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Types of hormones

• Peptides
• Chains of amino acids
• 4 200 amino acids
• Water soluble
• Largest of hormones
• Hypothalamus
• Pituitary (Ant. Post.)
• Islets of Langerhans
• Parathyroid hormone
• Digestive system hormones

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Peptide/protein hormone synthesis
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Types of hormones

• Amino Acid Based
• Tyrosine derivatives
• Thyroid hormones
• Thyroxine (T4)
• Triiodothyronine (T3)
• Catecholamines/Adrenal medulla
• Epinephrine
• Norepinephrine
• Both neurohormones neurotransmitter
• Tryptophan derivatives (precursor to serotonin
  and the pineal hormone melatonin)
• Glutamic acid (converted to histamine)

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Types of hormones

• Steroids
• Derivatives of cholesterol differing in side
  chains
• Four covalently-bonded rings
• Lipid soluble (freely diffuse, not stored, not
  packaged)
• Adrenal cortex
• Gonads
• Examples
• Glucocorticoids (cortisol major representative in
  mammals)
• Mineralocorticoids (aldosterone most prominent)
• Androgens (i.e. testosterone)
• Estrogens (i.e. estradiol and estrone)
• Progestogens (i.e. progestins)

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Types of hormones

• Fatty Acid Derivatives - Eicosanoids
• Eicosanoids are a large group of molecules
  derived from polyunsaturated fatty acids.
• The principal groups of hormones of this class
  are prostaglandins, prostacyclins, leukotrienes
  and thromboxanes.

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How does hormone type affect its activation of
target cells?
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Mechanisms of Hormone Action

• Lipid-soluble steroids thyroid hormones
• Diffuse through plasma membrane
• Enter nucleus
• Forms hormone-receptor complex
• H-R complex binds as transcription factors to
  chromosome to activate/inactivate gene(s)

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Mechanisms of Hormone Action

• Peptides water-soluble amines
• Hormone (A) binds to receptor on cell surface
• Activates G- protein
• Activates adenylate cyclase
• Converts ATP to cAMP
• cAMP activates protein kinases, which produce
  final effect.

Signal Transduction Pathway Animation
Transduction Pathway Epinephrine
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Mechanisms of Hormone Action

• Peptides water-soluble amines
• Other Hormone (B) binds to receptor on cell
  surface
• Activates G- protein
• Inhibits adenylate cyclase
• Stops ATP to cAMP
• ? inhibits final effect of first hormone

Which cells are activated by hormones?
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Hormone Targets

• A cell is a target because is has a specific
  receptor for the hormone
• Most hormones circulate in blood, coming into
  contact with essentially all cells. However, a
  given hormone usually affects only a limited
  number of cells, which are called target cells.
• A target cell responds to a hormone because it
  bears receptors for the hormone.

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Which diagram represents Steroid
hormones? Lipid hormones? Peptide hormones?
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Target cell concept
Receptor
Target cell
Hormone
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Target cell concept
Not all hormonesfind their target How are
chemical signals sent to cells?
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Types of cell-to-cell signaling

• Classic endocrine hormones travel via bloodstream
  to target cells
• Neurohormones are released via synapses and
  travel via the bloostream
• Paracrine hormones act on adjacent cells
• Autocrine hormones are released and act on the
  cell that secreted them
• Intracrine hormones act within the cell that
  produces them

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Response vs. distance traveled
Endocrine action the hormone is distributed in
blood and binds to distant target
cells. Paracrine action the hormone acts
locally by diffusing from its source to target
cells in the neighborhood. Autocrine action the
hormone acts on the same cell that produced it.
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Ways of influencing target cells
Within beside/near self close to
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(No Transcript)
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Create a Venn diagram comparing the nervous
endocrine systems
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Endocrine vs. Nervous System

• Major communication systems in the body
• Integrate stimuli and responses to changes in
  external and internal environment
• Both are crucial to coordinated functions of
  highly differentiated cells, tissues and organs
• Unlike the nervous system, the endocrine system
  is anatomically discontinuous.

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Nervous Sys. vs Endocrine Sys.

• The nervous system exerts point-to-point control
  through nerves, similar to sending messages by
  conventional telephone. Nervous control is
  electrical in nature and fast.
• The endocrine system broadcasts its hormonal
  messages to essentially all cells by secretion
  into blood and extracellular fluid. Like a radio
  broadcast, it requires a receiver to get the
  message - in the case of endocrine messages,
  cells must bear a receptor for the hormone being
  broadcast in order to respond.

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Regulation of hormone secretion

• Sensing and signaling a biological need is
  sensed, the endocrine system sends out a signal
  to a target cell whose action addresses the
  biological need. Key features of this stimulus
  response system are
•         receipt of stimulus
•         synthesis and secretion of hormone
•         delivery of hormone to target cell
•         evoking target cell response
•         degradation of hormone

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Receipt of Stimulus

• Humoral? in response to changing blood levels
• i.e. PTH regulation of Ca2 via parathyroid
• Neural? in response to nerve fibers
• i.e. catecholamines (norepinephrine
  epinephrine) from adrenal medulla
• Hormonal? in response to other hormones
• i.e. GHRH secreted by hypothalamus which
  regulates GH secretion by anterior pituitary

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Inputs to endocrine cells
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Control of Endocrine Activity

• The concentration of hormone as seen by target
  cells is determined by three factors
• Rate of production
• Rate of delivery
• Permissiveness/Synergism/Antagonism
• Upregulation (insipidus)/downregulation (Type II,
  melitus)
• Rate of degradation and elimination
• What is a feedback loop?

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Feedback Control of Hormone Production

• Feedback loops are used extensively to regulate
  secretion of hormones
• Negative feedback occurs when a change in a
  physiological variable triggers a response that
  counteracts the initial fluctuation

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Negative Feedback

• Neurons in the hypothalamus secrete thyroid
  releasing hormone (TRH), which stimulates cells
  in the anterior pituitary to secrete
  thyroid-stimulating hormone (TSH)
• TSH binds to receptors on epithelial cells in the
  thyroid gland, stimulating synthesis and
  secretion of thyroid hormones, which affect
  probably all cells in the body
• When blood concentrations of thyroid hormones
  increase above a certain threshold, TRH-secreting
  neurons in the hypothalamus are inhibited and
  stop secreting TRH.

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Feedback control

• Negative feedback is most common for example, LH
  from pituitary stimulates the testis to produce
  testosterone which in turn feeds back and
  inhibits LH secretion
• Positive feedback is less common examples
  include LH stimulation of estrogen which
  stimulates LH surge at ovulation

Positive Negative Feedback
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Diseases of the Endocrine System

• Cushing's Syndrome
• Acromegaly
• Pheochromocytoma
• Glucagonoma
• Somatostatinoma
• Diabetes mellitus
• Diabetes insipidus
• Hyperthyroidism (Graves disease)
• Hypothyroidism (Goiter)
• Hypothyroidism (Cretinism in babies)
• Hypothyroidism (Myxedema)
• Achondroplasia (Dwarfism)
• Gigantism
• SADS (Seasonal Affective Disorder)

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Disorders of the Endocrine System

• Acromegaly Simple Goiter

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Disorders of the Endocrine System

• Cushings Disease Achondroplasia