Chapter 45 Hormones and the Endocrine System

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Chapter 45 Hormones and the Endocrine System

• Barbara Musolf
• Clayton State University
• AS Building G 110-G
• 678-466-4851

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Objectives

• Interactions of the endocrine and nervous system
  in regulating animals physiology
• Mechanisms of hormone actions
• The role of the hypothalamus and pituitary in
  regulating the endocrine system
• The role of hormones in regulating metabolism,
  homeostasis, development and behavior.
• Invertebrate regulatory systems

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Intercellular communication

• The endocrine system releases hormones into the
  blood.
• Hormones can reach all cells
• The spread of hormones takes time
• The action of hormones can be prolonged
• The nervous system releases neurotransmitters
  that affect specific neuronal cells.
• Neurotransmitters reach few cells
• The response is rapid
• The action is brief

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Endocrine system

• All the hormone secreting cells make up the
  endocrine system
• Hormone secreting organs are called endocrine
  glands
• Chemicals are released into the blood and
  extracellular space.
• Regulate homeostatic processes
• Regulate developmental processes
• Male and female characteristics
• Adult and juvenile characteristics

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Nervous system overlap

• Neurosecretory cells found in the brain also
  release hormones called neurohormones
• Some of these chemical hormones also function as
  neurotransmitters.
• Nervous system plays a role in regulating some
  parts of the endocrine system
• Regulation of circadian and seasonal rhythms
• Regulation of reproductive cycles

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Intercellular signaling Fig. 45.2a

• Simple endocrine pathway
• Release of the signal molecule is into the blood.

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Intercellular signaling Fig. 45.2b

• Simple endocrine pathway
• Release of the signal molecule is into
  intercellular space.

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Intercellular signaling Fig. 45.2b

• Simple endocrine pathway
• Release of the signal molecule is into
  intercellular space.

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Intercellular signaling Fig. 45.2c

• Synaptic signaling from presynaptic cell to
  postsynaptic cell
• Release of the signal molecule is at a synapse.

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Intercellular signaling Fig. 45.2d

• Synaptic signaling from presynaptic cell to
  postsynaptic cell
• Release of the signal molecule is at a synapse.

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Intercellular signaling Fig. 45.2d

• Neurosecretory signaling
• A presynaptic cell releases signal molecule into
  the blood.
• Signal travels to distant targets

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Types of secreted signaling hormones

• Hormones convey signals through the blood stream.
• Paracrine hormones signal local cells
• Autocrine hormones target the secreting cell
• Neurotransmitters and neurohormones
• 3 classes of hormones
• Proteins and peptides (under 30 AAs)
• Amines (derived from a single AA)
• Steroids
• Pheromones are volatile signals between organisms

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Chemical classes of hormones

• Water soluble hormones bind to plasma membrane
  receptors
• Steroid hormones bind to intracellular receptors

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Where is the receptor for MSH?
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Water soluble hormones Fig. 45.5a

• Intracellular response can be
• Activation of an enzyme
• Change in uptake or secretion of chemicals
• Rearrangement of cytoskeleton
• Transcription of particular genes

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Water soluble hormones

• Can activate second messenger pathways

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Lipid soluble hormonesFig. 45.5b

• Diffusion
• Formation of hormone/receptor complex
• Activation of transcription
• Production of mRNA

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Different effects from one hormone
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Local regulators

• Act faster, use the same pathways
• Cytokines enhance immune responses
• Growth factor stimulates proliferation and
  differentiation
• NO promotes vasodilation
• Prostaglandins enhance smooth muscle contractions

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Human endocrine glands
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Simple hormonal pathway
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Glucose homeostasis

• Glucagon and insulin are produced in 2 of the
  cells in the pancreas
• Islets of Langerhans are scattered throughout the
  pancreas
• Glucagon is produced by alpha cells
• Insulin is produced by beta cells
• Glucagon and insulin are antagonistic hormones
  that regulate glucose in the blood at 90mg/100mL

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Effects of insulin and glucagon

• Insulin stimulates all body cells except brain
  cells to take up glucose
• Insulin slows glycogen breakdown in the liver
• Insulin inhibits gluconeogenesis and production
  of glucose from glycerol.
• Glucagon increases glucose in the blood.
• Glucagon stimulates hydrolysis of glycogen in the
  liver and conversion of AAs and glycerol to
  glucose
• Only liver cells are sensitive to glucagon.

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Glucose homeostasis
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Diabetes

• Diabetes mellitus has two different causes
• Type I the immune system destroys beta cells
  leading to lack of insulin
• Type II is a deficiency of insulin or reduced
  sensitivity of insulin receptors
• Glucose levels in the blood exceed the
  reabsorbing abilities of the kidney
• The body turns to fat to produce glucose, which
  produces acidic blood (ketosis)

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Endocrine and nervous system interactions in
invertebrates

• Hormones control sexual and asexual reproduction
  in hydra
• In Aplysia a neurohormone stimulates laying of
  eggs and inhibits appetite and locomotion
• Crustaceans and insects have hormones that
  regulate molting

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Endocrine and nervous system interactions in
vertebrates
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Hypothalamus and posterior pituitary

• The hypothalamus is the neural integrator
• Axons project to posterior pituitary and release
  neurohormones
• Antidiuretic hormone (ADH)
• Oxytocin

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Hypothalamus and anterior pituitary
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Anterior pituitary Tropic hormones

• Gonadotropins--Follicle stimulating hormone (FSH)
  and leutinizing hormone (LH) stimulate activities
  of ovaries and testes
• Thyroid stimulating hormone (TSH) stimulates
  production and relase of thyroid hormones
• Adrenocorticotropic hormone (ACTH) promotes
  production and secretion of steroid hormones from
  the adrenal gland.

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Anterior pituitary Nontropic hormones

• Prolactin stimulates mammary gland growth and
  milk synthesis in mammals.
• Melanocyte stimulating hormone inhibits hunger
• b-endorphins dull the perception of pain

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Anterior pituitaryGrowth hormone

• GH acts on the liver to release insulin-like
  growth factors (IGFs)
• Stimulates bone and cartilage growth
• Raises blood glucose levels
• Hypersecretion leads to gigantism
• Hyposecretion leads to pituitary dwarfism

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Thyroid hormones

• Thyroid gland produces triiodothyronine (T3) and
  thyroxine (T4).
• Secretes mostly T4, which is converetd to T3 by
  target cells.
• T3 has a higher affinity for the receptor
• Hypothalamus and pituitary control secretion of
  thyroid hormones

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Thyroid hormone

• Plays an important role in development
• Controls metamorphosis of tadpole into frog.
• Required in bone formation and branching of
  neurons during development
• Inherited conditions of thyroid deficiency can
  lead to cretinism
• Maintains homeostasis in blood pressure, heart
  rate, muscle tone, digestion and reproduction
• TH increases oxygen use and cellular metabolism.
• Graves disease is hyperthyroidism.
• Hypothyroidism leads to weight gain, lethargy

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Thyroid hormones calcitonin

• Calcitonin is secreted from parafollicular cells
  of thyroid.
• Calcitonin is important in calcium homeostasis.
• Increases activity of osteoblasts that increase
  bone deposition.

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Parathyroid hormones

• The parathyroid glands in humans are collections
  of cells embedded in the dorsal surface of the
  thyroid gland.
• Parathyroid hormone (PTH) leads to release of
  calcium into the blood.
• Acts on osteoclasts that breakdown bone
• Inhibits osteoblast activity
• Stimulates liver and kidney to produce calcitriol
  from Vitamin D
• Calcitriol increases absorption of calcium in the
  GI tract.

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Calcium homeostasis

• Calcium maintained between 9-11 mg/100 mL

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Adrenal Hormones

• Adrenal cortex is an endocrine gland
• Adrenal medulla is a neuroendocrine gland

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Adrenal gland and short term stress
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Adrenal gland and long term stress
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Gonadal sex hormones

• Gonads produce androgens, estrogens and
  progestins.
• Proportions are different in males and females
• Androgens (testosterone) stimulate development
  and help maintain male reproductive system.
• In utero they lead to development of males
• During puberty they are responsible for secondary
  sex characteristics
• Estrogens (estradiol) is responsible for
  maintenance of female reproductive system and
  development of secondary sex characteristics
• Progestins prepare and maintain the uterus.

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The pineal gland and melatonin

• The pineal gland is located centrally in
  vertebrate brain, often close to the surface.
• In some organisms, the cells are light sensitive,
  others have input from light sensing regions of
  the hypothalamus.
• The pineal gland secretes melatonin during dark
  hours
• It is linked to a biological clock that regulates
  daily and seasonal rhythms
• Melatonin feeds back to the region of the
  hypothalamus called the suprachiasmatic nucleus
  (SCN)