The marine iguana (Amblyrhynchus cristatus)

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The marine iguana (Amblyrhynchus cristatus)
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Common Aspects of Neural and Endocrine Regulation

• APs are chemical events produced by diffusion of
  ions through neuron plasma membrane.
• Action of some hormones are accompanied by ion
  diffusion and electrical changes in the target
  cell.
• Nerve axon boutons release NTs.
• Some chemicals are secreted as hormones, and also
  are NTs.
• In order for either a NT or hormone to function
  in physiological regulation
• Target cell must have specific receptor proteins.
• Combination of the regulatory molecule with its
  receptor proteins must cause a specific sequence
  of changes.
• There must be a mechanism to quickly turn off the
  action of a regulator.

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Endocrine Glands and Hormones

• Secrete biologically active molecules into the
  blood.
• Lack ducts.
• Carry hormones to target cells that contain
  specific receptor proteins for that hormone.
• Target cells can respond in a specific fashion.

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Endocrine Glands and Hormones (continued)

• Neurohormone
• Specialized neurons that secrete chemicals into
  the blood rather than synaptic cleft.
• Chemical secreted is called neurohormone.
• Hormones
• Affect metabolism of target organs.
• Help regulate total body metabolism, growth, and
  reproduction.

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Chemical Classification of Hormones

• Amines
• Hormones derived from tyrosine and tryptophan.
• NE, Epi, T4.
• Polypeptides and proteins
• Polypeptides
• Chains of lt 100 amino acids in length.
• ADH.
• Protein hormones
• Polypeptide chains with gt 100 amino acids.
• Growth hormone.

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Chemical Classification of Hormones (continued)

• Lipids derived from cholesterol.
• Are lipophilic hormones.
• Testosterone.
• Estradiol.
• Cortisol.
• Progesterone.

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Chemical Classification of Hormones (continued)

• Glycoproteins
• Long polypeptides (gt100) bound to 1 or more
  carbohydrate (CHO) groups.
• FSH and LH.
• Hormones can also be divided into
• Polar
• H20 soluble.
• Nonpolar (lipophilic)
• H20 insoluble.
• Can gain entry into target cells.
• Steroid hormones and T4.
• Pineal gland secretes melatonin
• Has properties of both H20 soluble and lipophilic
  hormones.

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Chemical Classification of Hormones (continued)

• Steroid hormones- lipid soluble
• Synthesize from cholesterol
• Invertebrates--Molting hormone
• Vertebrates gonads and adrenal cortex
• Peptide and protein hormones-transported via
  carrier proteins
• Invertebrates gamete-shedding hormones
• Vertebrates-- ADH, insulin, growth hormone
• Amine hormones
• Melatonin, catecholamines, and iodothyronines

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Prohormones and Prehormones

• Prohormone
• Precursor is a longer chained polypeptide that is
  cut and spliced together to make the hormone.
• Proinsulin.
• Preprohormone
• Prohormone derived from larger precursor
  molecule.
• Preproinsulin.
• Prehormone
• Molecules secreted by endocrine glands that are
  inactive until changed into hormones by target
  cells.
• T4 converted to T3.

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Hormonal Interactions

• Synergistic
• Two hormones work together to produce a result.
• Additive
• Each hormone separately produces response,
  together at same concentrations stimulate even
  greater effect.
• NE and Epi.
• Complementary
• Each hormone stimulates different step in the
  process.
• FSH and testosterone.

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Hormonal Interactions (continued)

• Permissive effects
• Hormone enhances the responsiveness of a target
  organ to second hormone.
• Increases the activity of a second hormone.
• Prior exposure of uterus to estrogen induces
  formation of receptors for progesterone.
• Antagonistic effects
• Action of one hormone antagonizes the effects of
  another.
• Insulin and glucagon.

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Effects of Hormone on Tissue Response

• Hormone in blood reflects the rate of
  secretion.
• Half-life
• Time required for the blood hormone to be
  reduced to ½ reference level.
• Minutes to days.
• Normal tissue responses are produced only when
  hormone are present within physiological range.
• Varying hormone within normal, physiological
  range can affect the responsiveness of target
  cells.

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Effects of Hormone on Tissue Response
(continued)

• Priming effect (upregulation)
• Increase number of receptors formed on target
  cells in response to particular hormone.
• Greater response by the target cell.
• Desensitization (downregulation)
• Prolonged exposure to high polypeptide hormone.
• Subsequent exposure to the same hormone
  produces less response.
• Decrease in number of receptors on target cells.
• Insulin in adipose cells.
• Pulsatile secretion may prevent downregulation.

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Mechanisms of Hormone Action

• Hormones of same chemical class have similar
  mechanisms of action.
• Similarities include
• Location of cellular receptor proteins depends on
  the chemical nature of the hormone.
• Events that occur in the target cells.
• To respond to a hormone
• Target cell must have specific receptors for that
  hormone (specificity).
• Hormones exhibit
• Affinity (bind to receptors with high bond
  strength).
• Saturation (low capacity of receptors).

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Hormones That Bind to Nuclear Receptor Proteins

• Lipophilic steroid and thyroid hormones are
  attached to plasma carrier proteins.
• Hormones dissociate from carrier proteins to pass
  through lipid component of the target plasma
  membrane.
• Receptors for the lipophilic hormones are known
  as nuclear hormone receptors.

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Nuclear Hormone Receptors

• Steroid receptors are located in cytoplasm and in
  the nucleus.
• Function within cell to activate genetic
  transcription.
• Messenger RNA directs synthesis of specific
  enzyme proteins that change metabolism.
• Each nuclear hormone receptor has 2 regions
• A ligand (hormone)-binding domain.
• DNA-binding domain.
• Receptor must be activated by binding to hormone
  before binding to specific region of DNA called
  HRE (hormone responsive element).
• Located adjacent to gene that will be transcribed.

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Mechanisms of Steroid Hormone Action

• Cytoplasmic receptor binds to steroid hormone.
• Translocates to nucleus.
• DNA-binding domain binds to specific HRE of the
  DNA.
• Dimerization occurs.
• Process of 2 receptor units coming together at
  the 2 half-sites.
• Stimulates transcription of particular genes.

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Mechanism of Thyroid Hormone Action

• T4 passes into cytoplasm and is converted to T3.
• Receptor proteins located in nucleus.
• T3 binds to ligand-binding domain.
• Other half-site is vitamin A derivative
  (9-cis-retinoic) acid.
• DNA-binding domain can then bind to the half-site
  of the HRE.
• Two partners can bind to the DNA to activate HRE.
• Stimulate transcription of genes.

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Hormones That Use 2nd Messengers

• Hormones cannot pass through plasma membrane use
  2nd messengers.
• Catecholamine, polypeptide, and glycoprotein
  hormones bind to receptor proteins on the target
  plasma membrane.
• Actions are mediated by 2nd messengers
  (signal-transduction mechanisms).
• Extracellular hormones are transduced into
  intracellular 2nd messengers.

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Adenylate Cyclase-cAMP (continued)

• Phosphorylates enzymes within the cell to produce
  hormones effects.
• Modulates activity of enzymes present in the
  cell.
• Alters metabolism of the cell.
• cAMP inactivated by phosphodiesterase.
• Hydrolyzes cAMP to inactive fragments.

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Adenylate Cyclase-cAMP

• Polypeptide or glycoprotein hormone binds to
  receptor protein causing dissociation of a
  subunit of G-protein.
• G-protein subunit binds to and activates
  adenylate cyclase.
• ATP cAMP PPi
• cAMP attaches to inhibitory subunit of protein
  kinase.
• Inhibitory subunit dissociates and activates
  protein kinase.

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Synthesis, storage, and release of hormones

• Peptide hormones
• Synthesized by transcription of DNA, translation
  and post-translational processing
• Steroid hormones
• Synthesized from cholesterol
• Not stored, synthesize on demand
• Secreted by diffusion through cell membrane

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Figure 14.4 Snapshots of insulin synthesis,
processing, and packaging (Part 1)
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Figure 14.4 Snapshots of insulin synthesis,
processing, and packaging (Part 2)
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Pituitary Gland

• Pituitary gland is located in the diencephalon.
• Structurally and functionally divided into
• Anterior lobe.
• Posterior lobe.

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The mammalian pituitary gland

• Pars nervosa- posterior pituitary
• Contains terminals of axons
• Secretory cells located in hypothalamus
• Anterior pituitary
• Nonneural endocrine cells
• Secretion controlled by hypothalamo-hypophyseal
  portal system
• Separate populations of cells secrete different
  hormones

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Hypothalamic Control of Posterior Pituitary

• Hypothalamus neuron cell bodies produce
• ADH supraoptic nuclei.
• Oxytocin paraventricular nuclei.
• Transported along the hypothalamo-hypophyseal
  tract.
• Stored in posterior pituitary.
• Release controlled by neuroendocrine reflexes.

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Figure 14.6 The vertebrate pituitary gland has
two parts (Part 1)
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Pituitary Hormones (continued)

• Posterior pituitary
• Stores and releases 2 hormones that are produced
  in the hypothalamus
• Antidiuretic hormone (ADH/vasopressin)
• Promotes the retention of H20 by the kidneys.
• Less H20 is excreted in the urine.
• Oxytocin
• Stimulates contractions of the uterus during
  parturition.
• Stimulates contractions of the mammary gland
  alveoli.
• Milk-ejection reflex.

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Pituitary Gland (continued)

• Posterior pituitary(neurohypophysis)
• Formed by downgrowth of the brain during fetal
  development.
• Is in contact with the infundibulum.
• Nerve fibers extend through the infundibulum.
• Anterior pituitary
• Adenohypophysis
• Derived from a pouch of epithelial tissue that
  migrates upward from the mouth.

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Pituitary Hormones

• Anterior Pituitary
• Trophic effects
• High blood hormone causes target organ to
  hypertrophy.
• Low blood hormone causes target organ to
  atrophy.

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Hypothalamic Control of the Anterior Pituitary

• Hormonal control rather than neural.
• Hypothalamus neurons synthesize releasing and
  inhibiting hormones.
• Hormones are transported to axon endings of
  median eminence.
• Hormones secreted into the hypothalamo-hypophyseal
  portal system regulate the secretions of the
  anterior pituitary

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Figure 14.6 The vertebrate pituitary gland has
two parts (Part 2)
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Figure 14.6 The vertebrate pituitary gland has
two parts (Part 3)
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Figure 14.6 The vertebrate pituitary gland has
two parts (Part 4)
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Figure 14.6 The vertebrate pituitary gland has
two parts (Part 5)
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Feedback Control of the Anterior Pituitary

• Anterior pituitary and hypothalamic secretions
  are controlled by the target organs they
  regulate.
• Secretions are controlled by negative feedback
  inhibition by target gland hormones.
• Negative feedback at 2 levels
• The target gland hormone can act on the
  hypothalamus and inhibit secretion of releasing
  hormones.
• The target gland hormone can act on the anterior
  pituitary and inhibit response to the releasing
  hormone.

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Feedback Control of the Anterior Pituitary
(continued)

• Short feedback loop
• Retrograde transport of blood from anterior
  pituitary to the hypothalamus.
• Hormone released by anterior pituitary inhibits
  secretion of releasing hormone.
• Positive feedback effect
• During the menstrual cycle, estrogen stimulates
  LH surge.

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Higher Brain Function and Pituitary Secretion

• Axis
• Relationship between anterior pituitary and a
  particular target gland.
• Pituitary-gonad axis.
• Hypothalamus receives input from higher brain
  centers.
• Psychological stress affects
• Circadian rhythms.
• Menstrual cycle.

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Figure 14.7 The adrenal gland consists of an
inner medulla and an outer cortex
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Figure 14.8 Both hormonal and neural mechanisms
modulate the action of the HPA axis
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Figure 14.9 Interactions of insulin, glucagon,
and epinephrine
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Figure 14.10 The mammalian stress response (Part
1)
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Figure 14.10 The mammalian stress response (Part
2)
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Figure 14.11 The CNS and the immune system
interact during the stress response
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The CNS and the immune system interact during the
stress response

• Cytokines released from certain cells of the
  immune system
• Binds with specific receptor molecules
• Travel in the blood to hypothalamus
• Stimulate CRH neurosecretory cells
• Resulting in the physiological responses of the
  HPA axis
• Helps fight infection
• Glucocorticoids inhibit the production of agents
  that cause inflammation-modulating the immune
  response

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Endocrine control of nutrient metabolism in
mammals

• Insulin secreted when nutrients molecules are
  abundant
• Hypoglycemic effect- promote uptake of nutrients
• Inhibit degradation of glycogen, lipids and
  proteins
• Glucagon secreted when glucose level is low
• Hyperglycemic effect- stimulate break down of
  glycogen, triglyceride molecules
• Forms glucose from noncarbohydrate sources
• Growth hormone, glucocorticoids, epinephrine,
  thyroid hormones play permissive and synergistic
  roles in nutrient metabolism

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Figure 14.12 Hormone nutrient levels in blood
of healthy humans before after a meal (Part 1)
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Figure 14.12 Hormone nutrient levels in blood
of healthy humans before after a meal (Part 2)
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Figure 14.13 The action of an antidiuretic
hormone (Part 1)
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Figure 14.13 The action of an antidiuretic
hormone (Part 2)
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Figure 14.14 The reninangiotensinaldosterone
system (Part 1)
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Figure 14.14 The reninangiotensinaldosterone
system (Part 2)
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Endocrine control of salt and water balance in
vertebrates

• Vasopressin (ADH)- peptide neurohormone
• Stimulate conservation of water
• Aldosterone
• Stimulate conservation of Na
• Part of renin-angiotensin-aldosterone system
• ANP- atrial natriuretic peptide
• Stimulate the excretion of Na and water

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Figure 14.15 Chemical messengers act over short,
intermediate, and long distances
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Figure 14.16 Two types of metamorphosis
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Figure 14.17 The silkworm Bombyx mori goes
through holometabolous development
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Insect metamorphosis part 1

• Three hormones control metamorphosis
• Prothoracicotropic hormone PTTH
• Ecdysone
• Juvenile hormone JH
• Secreted by nonneural endocrine cells
• Prevents metamorphosis in the adult form
• In adult, stimulates sex-attractant pheromones
• Additional hormones
• Bursicaon darkening and hardening of the
  cuticle
• Eclosion hormone (EH)
• Pre-ecdysis triggering hormone (PETH)
• Ecdysis triggering hormone (ETH)
• Control stereotyped movements during ecdysis

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Insect metamorphosis part 2

• Convergent evolution of endocrine and
  neuroendocrine functions between vertebrate and
  invertebrate animals
• Hemimetabolous insects go through gradual
  metamorphosis
• Holometabolous insects go through complete
  metamorphosis
• Environmental and behavioral signals mediated by
  the nervous system initiate molting

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Insect metamorphosis part 3

• Neuroendocrine cells in the brain secrete PTTH
• Stimulates secretion of ecdysone from the
  prothoracic glands
• Ecdysone is converted to 20-hydroxyecdysone by
  peripheral activation
• Epidermis secrete enzymes required for molting
  process

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Figure 14.19 Endocrine neuroendocrine
structures involved in control of insect
metamorphosis (1)
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Figure 14.19 Endocrine neuroendocrine
structures involved in control of insect
metamorphosis (2)