Animal Hormones

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Animal Hormones
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Concept 30.1 Hormones Are Chemical Messengers

• Endocrine secretioncells secrete substances into
  the extracellular fluid
• Exocrine secretioncells secrete substances into
  a duct or a body cavity that communicates to the
  external world

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Concept 30.1 Hormones Are Chemical Messengers

• Endocrine cellscells that secrete endocrine
  signals
• Some endocrine cells exist as single cells (e.g.,
  in the digestive tract).
• Endocrine glandssecretory organs composed of
  aggregations of endocrine cells

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Concept 30.1 Hormones Are Chemical Messengers

• Endocrine signaling molecules are paracrine
  signals, autocrine signals, or hormones.
• Hormones are long-distance endocrine signals
  that are released into the bloodstream and
  circulate throughout the body.

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Concept 30.1 Hormones Are Chemical Messengers

• Target cellscells that have receptors for the
  chemical signals
• The same hormone can have a variety of different
  target cells, all distant from the site of
  release.

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Concept 30.1 Hormones Are Chemical Messengers

• Hormones are in three chemical groups
• Peptide and protein hormoneswater-soluble,
  transported in blood with receptors on exterior
  of target cells
• Steroid hormonessynthesized from cholesterol
  lipid-soluble bound to carrier proteins in
  blood receptors inside target cells

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Concept 30.1 Hormones Are Chemical Messengers

• Amine hormonessynthesized from single amino
  acids may be lipid-soluble or water-soluble,
  depending on the charge of the amino acid

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Figure 30.1 Three Classes of Hormones (Part 1)
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Figure 30.1 Three Classes of Hormones (Part 2)
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Figure 30.1 Three Classes of Hormones (Part 3)
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Concept 30.1 Hormones Are Chemical Messengers

• Chemical communication was critical for evolution
  of multicellular organisms.
• Plants, sponges, and protists all use chemical
  signals.
• Signaling molecules are highly conserved, but
  their functions differ.

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Concept 30.1 Hormones Are Chemical Messengers

• In arthropods, hormones control molting and
  metamorphosis
• The rigid exoskeleton is shed during molts to
  allow growth.
• Growth stages between molts are called instars.

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Figure 30.2 A Diffusible Substance Triggers
Molting (Part 1)
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Figure 30.2 A Diffusible Substance Triggers
Molting (Part 2)
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Concept 30.1 Hormones Are Chemical Messengers

• Two hormones regulate molting
• PTTH (prothoracicotropic hormone), from cells in
  the brain, is stored in the corpora cardiaca
• PTTH stimulates the prothoracic gland to secrete
  ecdysone.
• Ecdysone diffuses to target tissues and
  stimulates molting.

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Concept 30.1 Hormones Are Chemical Messengers

• A third hormone, juvenile hormone, is also
  released from the brainprevents maturation to
  adult form.
• Control of development by juvenile hormone is
  important in insects with complete metamorphosis.

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Figure 30.3 Hormonal Control of Metamorphosis
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Concept 30.2 Hormones Act by Binding to Receptors

• Hormone receptors can be membrane-bound with
  three domains
• Binding domainprojects outside plasma membrane
• Transmembrane domainanchors receptor
• Cytoplasmic domainextends into cytoplasm,
  initiates target cell response

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Concept 30.2 Hormones Act by Binding to Receptors

• Hormone receptors can also be intracellular
• Lipid soluble hormonesreceptors are inside the
  cell, usually in the cytoplasm
• When hormone binds, the hormonereceptor complex
  moves into the nucleus.

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Concept 30.2 Hormones Act by Binding to Receptors

• One hormone can trigger different responses in
  different types of cells.
• Epinephrine and norepinephrine are secreted by
  adrenal glands in the fight-or-flight response.
• These hormones bind to adrenergic receptors.

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Figure 30.4 The Fight-or-Flight Response
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Concept 30.2 Hormones Act by Binding to Receptors

• Two categories ?-adrenergic and ?-adrenergic
  receptors
• Stimulation of one receptor can cause diverse
  effects, depending on its location.
• Example ?-adrenergic stimulation causes
  sweating in skin and shutdown of digestive
  enzymes and decreased blood flow in gut.

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Figure 30.5 Adrenergic Receptors (Part 1)
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Figure 30.5 Adrenergic Receptors (Part 2)
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Concept 30.2 Hormones Act by Binding to Receptors

• Abundance of hormone receptors can be regulated
  by negative feedback.
• Downregulationcontinuous high level of hormone
  decreases number of receptors.
• Upregulationwhen hormone secretion is
  suppressed, receptors increase.

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Figure 30.6 The Human Endocrine System
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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems

• The nervous system communicates via
  moleculesneurotransmitters.
• The endocrine system communicates via molecules
  released into the blood.
• The systems are complementarynervous system is
  rapid and specific, endocrine system is broader
  and longer-term.

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neurotransmitter
hormone
hormone mediator molecule released in one part
of body but regulates activity in another part
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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems

• The nervous and endocrine systems also interact.
• Nervous system controls activity of many
  endocrine glands.
• Some neurons secrete hormones directlyneurohormon
  es.
• Endocrine system can also influence the nervous
  systemsteroids promote sexual behavior.

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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems

• The pituitary gland connects the nervous and
  endocrine systems.
• The pituitary gland is attached to the
  hypothalamus of the brain.
• Two partsthe anterior pituitary and posterior
  pituitary

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Figure 30.7 The Posterior Pituitary (Part 1)
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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems

• The hypothalamus secretes two neurohormones into
  the posterior pituitary antidiuretic hormone
  (vasopressin) and oxytocin.
• Antidiuretic hormone (ADH) serves to increase the
  water retained by the kidneys when necessary.
• Oxytocin stimulates contractions, milk flow,
  promotes bondingthe cuddle chemical

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Figure 30.7 The Posterior Pituitary (Part 2)
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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems

• The anterior pituitary secretes four tropic
  hormones that control other endocrine glands
• Thyroid-stimulating hormone (TSH)
• Luteinizing hormone (LH)
• Follicle-stimulating hormone (FSH)
• Adrenocorticotropin hormone (ACTH)

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Figure 30.8 The Anterior Pituitary
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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems

• The anterior pituitary also secretes other
  peptide hormones including prolactin and growth
  hormone.
• Growth hormone (GH) stimulates cells to take up
  amino acids.
• GH stimulates the liver to produce somatomedins
  or insulin-like growth factors (IGFs).
• Overproduction of GH causes gigantism
  underproduction causes pituitary dwarfism.

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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems
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Pituitary Hormones
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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems

• Neurohormones from the hypothalamus control
  subsequent hormone production in the anterior
  pituitary.
• The hypothalamus sends secretions to the anterior
  pituitary via the portal blood vessels.

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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems

• Hypothalamic neurohormones are released in minute
  quantities measurable by immunoassay.
• The first releasing hormone to be purified was
  thyrotropin-releasing hormone (TRH).
• TRH causes anterior pituitary cells to release
  thyroid-stimulating hormone (TSH).
• TSH causes the thyroid gland to release thyroxine.

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Concept 30.3 The Pituitary Gland Links the
Nervous and Endocrine Systems

• Negative feedback loops control hormone secretion
  from the anterior pituitary.
• Corticotropin is released by pituitaryadrenal
  produces cortisol in response.
• Circulating cortisol in bloodstream reaches
  pituitary and inhibits production.
• Hypothalamus slows release of corticotropin-releas
  ing hormone.

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Figure 30.9 Multiple Feedback Loops Control
Hormone Secretion
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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• The thyroid gland contains two cell types that
  produce two different hormones, thyroxine and
  calcitonin.
• In or near the thyroid gland are the parathyroid
  glands, which produce parathyroid hormone.
• Thyroxine (T4) is synthesized from the amino acid
  tyrosine and iodine.
• T3 is a similar hormone that is more active.

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• In birds and mammals, thyroxine raises metabolic
  rate.
• Thyroxine regulates cell metabolism by acting as
  a transcription factor for many genes and is
  crucial during development.
• Hypothalamus releases thyrotropin-releasing
  hormone (TRH), which causes anterior pituitary to
  secrete thyroid-stimulating hormone (TSH).
• TSH causes the thyroid to produce thyroxine.

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Goiter is an enlarged thyroid gland.

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Hyperthyroidism (thyroxine excess) is often
  caused by an autoimmune disease.
• Antibody-binding activates TSH receptors on
  follicle cells and increases thyroxine.
• Thyroid remains stimulated and grows bigger.

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Hypothyroidism (thyroxine deficiency) is the
  result of low circulating thyroxine.
• The most common cause is iodine
  deficiencythyroid cannot produce thyroxine.
• TSH levels remain high and stimulate the
  thyroid to grow bigger.

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Blood calcium concentration is controlled by
  calcitonin, calcitriol (from vitamin D), and
  parathyroid hormone (PTH).
• Mechanisms for changing calcium levels
• Deposition or absorption by bone
• Excretion or retention by kidneys
• Absorption of calcium from digestive tract

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Calcitonin, released by thyroid, lowers blood
  calcium (Ca2) by regulating bone turnover.
• Osteoclasts break down bone, increasing blood
  Ca2.
• Ca2 is deposited into bone by osteoblasts
  levels of Ca2 in blood decrease.
• Calcitonin decreases osteoclast activity and
  favors adding calcium to bones.

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Figure 30.11 Hormonal Regulation of Calcium
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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Vitamin D (calciferol) is synthesized from
  cholesterol in skin cells by UV light.
• Once synthesized it is converted to calcitriol, a
  hormone that stimulates calcium absorption from
  food.
• If light is insufficient, vitamin D must be
  obtained from diet or supplements.

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• The parathyroid glands secrete parathyroid
  hormone (PTH).
• PTH raises blood calcium levels
• Stimulates osteoclasts and osteoblasts
• Stimulates kidneys to reabsorb calcium
• Activates synthesis of calcitriol from vitamin D

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Each of the two adrenal glands is a gland within
  a gland.
• The core, or adrenal medulla, produces
  epinephrine and norepinephrine.
• Release of these neurohormones is under control
  of the nervous system and is very rapid in the
  stress response.

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Figure 30.12 The Adrenal Is a Gland within a
Gland
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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• The outer adrenal cortex produces two types of
  corticosteroid hormones
• Mineralocorticoids influence salt and water
  balance
• Aldosterone, the main mineralocorticoid,
  stimulates kidneys to conserve sodium and excrete
  potassium.

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Glucocorticoids influence blood glucose
  concentration
• Cortisol, the main glucocorticoid in humans and
  mammals, mediates metabolic stress response.
• After a stressful stimulus, blood cortisol rises.
• Cells not critical for action decrease their use
  of blood glucoseimmune system reactions are also
  blocked.

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems
Cushings
CAH
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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Gonads produce sex steroids.
• Androgensmale steroids, testosterone
• Estrogens and progesteronefemale steroids
• Both sexes use both types, in varying levels.
• In embryos, sex hormones determine sex of fetus
  at puberty, they stimulate maturation and
  secondary sex characteristics.

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Sex hormones exert their effects by the seventh
  week of human development.
• If a Y chromosome is present, gonads begin
  producing testosterone and MIS (Müllerian-inhibiti
  ng substance)these produce male reproductive
  organs and inhibit female reproductive
  structures.
• Without androgens, female reproductive structures
  develop.

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Figure 30.13 Sex Steroids Direct the Development
of Human Sex Organs (Part 1)
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Figure 30.13 Sex Steroids Direct the Development
of Human Sex Organs (Part 2)
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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• At puberty, production of sex hormones increases.
• Controlled by tropic hormones called
  gonadotropins from the anterior pituitary
• Luteinizing hormone (LH)
• Follicle-stimulating hormone (FSH)

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Concept 30.4 Hormones Regulate Mammalian
Physiological Systems

• Gonadotropins are controlled by hypothalamic
  gonadotropin-releasing hormone (GnrH)its release
  increases at puberty.
• Increase in gonadotropins leads to increase in
  sex steroids and development of secondary sex
  characteristics.

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Answer to Opening Question

• Hormones and their receptor complexes can have
  varying effects depending on the type of target
  cells.
• The receptors are essential because without them
  the circulating hormones are unable to have the
  desired effect.
• Hormones may also be modified during development,
  with different effects at different stages.

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Figure 30.14 Real People, Real Lives