Chemical Signals in Animals: Endocrine System and Hormonal Control

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Chemical Signals in Animals Endocrine System
and Hormonal Control
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Endocrine vs. Nervous

• The nervous system brings about immediate
  responses, but the endocrine system is slower
  acting and regulates processes that occur over
  days or even months.

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Hormones

• Endocrine systems exert control through the use
  of hormones.
• Hormones are chemical messengers produced by
  ductless glands in one part of the body which
  travel through the bloodstream and exert their
  influence in another part of the body.

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Hormones

• Hormones are secreted into the bloodstream and
  regulate whole body processes like growth,
  reproduction, complex behaviors including
  courtship and migration.
• Hormones influence the metabolism of their target
  cells by binding to receptor proteins within the
  cell or on the surface of the cell.

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Chemical Communication
Briefly describe the two major forms of
intercellular communication in animal bodies.
Which organ systems are responsible for this
communication? Describe the type of intercellular
communication called neuroendocrine. What
defines a target tissue?
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Basic Mechanisms of Chemical Signaling
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Exocrine vs. Endocrine

• Exocrine systems have ducts used for transport of
  substances directly into the body cavities
  salivary glands
• Endocrine systems are ductless and secrete
  hormones directly into body fluids pituitary
  gland

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Hormones

• The endocrine and the nervous systems are related
• 1) structurally
• 2) chemically
• 3) functionally
• simultaneously maintaining homeostasis,
  physiology and other body processes.

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Hormones

• Neurosecretory cells specialized nerve cells
  that secrete hormones located within endocrine
  organs and tissues.

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Hormones

• Several chemicals serve as both neurotransmitters
  and hormones.
• Epinephrine, produced by the adrenal medulla,
  acts as the fight or flight hormone and a
  neurotransmitter.

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Control

• Positive and Negative Feedback regulate
  mechanisms of both systems
• Positive feed back output intensifies and
  increases the likelihood of a response
• Mammal milk production and release

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Control

• - Antagonistic hormones work in opposition to one
  other.
• - Insulin and glucagon

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Hormonal Control

• Chemical signals operate at virtually all levels
  of organization
• Local regulators
• Intracellular
• Cell to cell
• Tissue to tissue regulators
• Organ to organ regulators
• Organism to organism (pheromones)

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Hormonal Control

• Local regulators affect neighboring target cells
• Histamine -- immune and regulatory responses
• Interleukins immune response
• Growth factors peptides and proteins that
  regulate the behavior of cells in growing and
  developing tissues
• Prostaglandins modified fatty acids released
  into interstitial fluid

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Hormonal Control

• Binding of a chemical signal to a specific
  receptor protein triggers chemical events in the
  target cell that result in a change in that cell.
• The response to a chemical signal depends on the
  number and affinity of the receptor proteins.

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Chemical Signals

• Chemical signals often bind to a specific protein
  receptor on the plasma membrane of the target
  cell
• Because of their chemical nature, most signal
  molecules (peptides, proteins, glycoproteins) are
  unable to diffuse through the plasma membrane

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Chemical Signals

• The binding of the signal molecule to a plasma
  membrane receptor initiates a signal transduction
  pathway, a series of events that converts the
  signal into a specific cellular response.

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Chemical Signals

• A specific example is the binding on the
  polypeptide hormone insulin to the insulin
  receptor
• Insulin binding initiates a chain of events that
  accounts for the blood sugar lowering effects of
  insulin.

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Vertebrate Endocrine System

• Coordinates
• 1)metabolism,
• 2)growth,
• 3)development, and
• 4)reproduction.

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Major Endocrine Organs
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Functions of Vertebrate Hormones

• Some hormones have a single action while other
  have multiple functions
• Tropic hormones act on other endocrine glands

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Functions of Vertebrate Hormones
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Functions of Vertebrate Hormones
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Hypothalamus

• Region of the lower brain
• Receives information from nerves throughout the
  body and brain
• Initiates endocrine signals appropriate to the
  environmental conditions
• Regulates the Pituitary Gland

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Pituitary Gland

• - Located at the base of the hypothalamus
• -Two lobes anterior and posterior numerous
  functions

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Anterior Pituitary Gland
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Anterior Pituitary Gland

• Produces many different hormones
• Regulated by factors of the hypothalamus
• Four are tropic hormones that stimulate other
  endocrine glands to synthesize and release their
  hormones TSH, ACTH, FSH, LH

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Anterior Pituitary Gland

• Luteinizing Hormone (LH)
• Stimulates ovulation and corpus luteum formation
  in females
• Stimulates spermatogenesis in males

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Anterior Pituitary Gland

• Follicle-Stimulating Hormone (FSH)
• Tropic hormone that affects the gonads
• In males, necessary for spermatogenesis
• In females, it stimulates ovarian follicle growth

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Anterior Pituitary Gland

• Growth Hormone (GH)
• Promotes growth directly
• Stimulates production of growth factors

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Anterior Pituitary Gland

• Thyroid-Stimulating Hormone (TSH)
• Tropic hormone that stimulates the thyroid gland
  to produce and secrete its own hormone

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Anterior Pituitary Gland

• Adrenocorticotropin (ACTH) stimulates the
  adrenal cortex to produce and secrete its steroid
  hormones
• Melanocyte-Stimulating Hormone (MSH) regulates
  the activity of pigment-containing skin cells
• Endorphins inhibit pain perception

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Posterior Pituitary Gland
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Posterior Pituitary Gland

• Synthesized in hypothalamus
• Secreted from posterior pituitary
• Oxytocin induces uterine muscle contraction
  induces lactation
• Antidiuretic Hormone acts on kidneys to
  increase water retention thus reducing urine
  volume

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Pineal Gland

• Small mass near the center of the brain
• Produces melatonin
• modified amino acid that modulates skin
  pigmentation
• secreted only at night larger amounts secreted
  in winter
• Involved in regulation of biorhythms

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Thyroid hormones function in 1) development
2) bioenergetics 3) homeostasis
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• Thyroid is on the ventral side of the trachea.
• plays a major role in vertebrate development
  participates in embryonic development
• control metamorphosis in amphibians

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Thyroid gland maintains homeostasis in mammals
including

• blood pressure
• heart rate
• muscle tone
• digestion
• reproductive functions
• rate of O2 consumption and metabolism (increases)

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Serious metabolic disorders result from
deficiency or excess of thyroid hormones.

• Hyperthyroidism - high body temperature,
  sweating, weight loss, irritability, high blood
  pressure
• Hypothyroidism can cause cretinism in infants
  and weight gain, lethargy, and cold-intolerance
  in adults
• Goiter - enlarged thyroid caused by a deficiency
  in iodine

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Thyroid hormone secretion is regulated by
hypothalamus and pituitary.

• Negative Feedback System.
• Hypothalamus secretes TRH ?
• Anterior Pituitary stimulated to produce TSH ?
• TSH binds to receptors and T3 and T4
• High levels of T3, T4, and TSH inhibit TRH

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Parathyroid hormone (PTH)

• balances blood calcium
• needs vitamin D to function

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Adrenal Glands

• located on top of kidneys
• Adrenal medula synthesizes catecholamines
• epinephrine
• norepinephrine
• Glucose is mobilized
• Heart rate is increased
• Bronchioles dilate

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Adrenal Glands

• Adrenal cortex synthesizes and secretes
  corticosteroids as directed by ACTH from the
  anterior pituitary
• Mineralocorticoids affect salt and water balance
• Aldosterone stimulates kidney cells to reabsorb
  sodium ions and water
• Glucocorticoids promote glucose synthesis from
  noncarbohydrate substances such as proteins

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Stress and The Adrenal Glands
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Steroids

• Androgens male sex hormones
• Testosterone
• Stimulate the development and maintenance of male
  reproductive systems
• responsible for secondary male sex
  characteristics

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Steroids

• Estrogens female sex hormones
• Maintain the female reproductive system
• responsible for secondary sex characteristics
• Progestins (Progesterone)
• Preparation and maintainace of uterus for
  reproduction
• Gonadotropins from anterior pituitary (FSH and
  LH) control the synthesis of both androgens and
  estrogens