Animal Endocrine Systems

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Animal Endocrine Systems

• Biology 2 Form and Function

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Hormones regulate...

• Together with nervous system, responsible for
  regulation of body organs
• Secreted by ductless glands into surrounding
  capillary network
• Long-term, narrow-to-broad impact mediated by
  contact of hormone with receptor molecules at
  target site
• Receptor molecules may be internal or external to
  cell
• Endocrine system is distinct to organ
  self-regulation, or autocrine/paracrine system

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There are four classes of hormone

• Polypeptides - short chains lt 100 amino acids in
  sequence, e.g., ADH
• Glycoproteins - long chains (100) of amino
  acids connected to carbohydrate, e.g., FSH
• Amines - derivatives of tyrosine and tryptophan,
  e.g., epinephrine, thyroxine
• Steroids - lipid derived
• sex steroids, e.g., testosterone
• corticosteroids, e.g., aldosterone

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In mammals, there is a close association between
the endocrine and neural systems...

• Nervous system-controlled endocrine glands
  include
• Adrenal medulla
• Posterior and anterior pituitary (via
  Hypothalamus)
• Pineal gland
• Examples of non-nervous system controlled
  endocrine secretion include pancreas (insulin),
  and adrenal cortex (aldosterone)

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Hormones that enter cells

• Includes all lipophilic (lipid-soluble) hormones
  (e.g., steroids, thyroxine)
• Bind to specific receptors in cytoplasm, which
  then moves to the nucleus, or binds directly to
  receptor proteins in nucleus
• Receptor molecule, once activated, binds to
  portions of DNA and stimulates transcription,
  ultimately effecting protein production and cell
  metabolism

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Hormones that do not enter cells...

• Water soluble hormones that bind to the outside
  of cell membranes, requiring a secondary
  messenger inside cell to complete message
• Secondary messengers include
• Cyclic AMP
• IP3/Ca2

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Cyclic AMP

• e.g., effects of epinephrine on b-adrenergic
  centers
• Binding of epinephrine to G-protein receptor
  causes G-protein sub-unit to disassociate
• G-protein sub-unit binds with membrane enzyme
  adenlyl cyclase
• Adenlyl cyclase, now activated, catalyzes
  formation of cAMP from ATP
• cAMP binds to and activates protein kinase-A,
  responsible for phosphorylation of certain
  proteins specific to tissue/cell
• in liver, stimulates conversion of glycogen to
  glucose
• In cardiac muscle, increases speed and force of
  heart beat

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Inositol triphosphate/Ca2

• e.g., effects of epinephrine on a-adrenergic
  centers
• Binding of epinephrine to G-protein receptor
  causes G-protein sub-unit to disassociate
• G-protein sub-unit binds with, and activates
  membrane enzyme phospholipase C
• Phospholipase C cleaves certain phospholipids to
  produce IP3
• IP3 binds with receptors on endoplasmic
  reticulum, stimulates release of Ca2
• Ca2 binds to calmodulin, which activates
  different types of protein kinases, causing
  phosphorylation of different cellular proteins

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The Posterior Pituitary

• neurally derived hormones are part of
  neuroendocrine reflex.
• Secretes Antidiuretic hormone (ADH) and Oxytocin
  (although both are made in the hypothalamus)
• ADH stimulates water retention by the kidneys
  (alcohol inhibits ADH, causing dehydration)
• Oxytocin stimulates uterine contractions and
  milk-ejection reflex

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Anterior pituitary

• Epithelially-derived tissue, produces
• GH, growth hormone (somatotropin)
• ACTH, adrenocorticotropic hormone (corticotropin)
• TSH, thyroid stimulating hormone (thyrotropin)
• Gonadotropins LH (luteinizing hormone) and FSH
  (follicle stimulating hormone)
• Prolactin (PRL)
• MSH, Melanocyte-stimulating hormone

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Control of the Anterior Pituitary by the
Hypothalamus is still hormone-mediated

• Releasing and inhibitory hormones are secreted by
  the hypothalamus and carried via a c apillary
  network connected to a second caillary network -
  the hypothalamo-hypophyseal portal system
• for example, gonadotropin releasing hormone
  (GnRH) stimulates the release of FSH and LH
• In turn, hypothalamus is controlled by negative
  feedback inhibition

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Other endocrine glands

• Adrenal glands
• The adrenal medulla secrets epinephrine and
  norepinephrine, triggering alarm responses across
  the body at various targets, preparing the body
  for fight or flight
• The adrenal cortex secretes cortisol and other
  glucocorticoids, an aid in glucose homeostasis,
  as well as aldosterone, responsible for salt
  balance

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The pancreas has both exocrine and endocrine
functions
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