ZOO 211

• Endocrine system


  Composed of endocrine glands and specialized endocrine cells located throughout the body
• Hormones


  Chemical messengers secreted by endocrine glands and cells into the bloodstream, rather than into a duct
• Target tissues


  Have receptors for a specific hormone and produce a particular response
• Endocrine System Glands


  • Figure 10.1
• Classes of Chemical Messengers

  • Autocrine
  • Paracrine
  • Neurotransmitter and neuromodulators
  • Hormones and neurohormones
• Endocrine System Functions


  • Regulation of metabolism
  • Control of food intake and digestion
  • Modulation of tissue development
  • Regulation of ion levels
  • Control of water balance
  • Regulation of cardiovascular function
  • Control of blood glucose and other nutrients
  • Control of reproductive functions
  • Stimulation of uterine contraction and milk release
  • Modulation of immune system function
• Types of Hormones


  • Water-soluble hormones
  • Lipid-soluble hormones
• Blood-borne chemicals can directly stimulate the release of some hormones


  These chemicals are referred to as humoral stimuli
• Hormone release can also be under neural control

  Following action potentials, neurons release a neurotransmitter into the synapse with the cells that produce the hormone
• Hormone release can also be controlled by other hormones


  A hormone is secreted that, in turn, stimulates the secretion of other hormones
• Control of Hormone Secretion

  • Humoral stimuli
  • Neural stimuli
  • Hormonal stimuli
• Humoral inhibition of hormone release generally involves the actions of companion hormones
• Neurons inhibit targets just as often as they stimulate targets
• Some hormones are inhibitory hormones, that reduce the release of the hormone being controlled
• Negative feedback


  Most hormones are regulated by a mechanism whereby the hormone's secretion is inhibited by the hormone itself once blood levels have reached a certain point
• Positive feedback


  Some hormones are regulated by a mechanism as exemplified by tropic hormone action
• Hormone Receptors and Mechanisms of Action

  • Receptor site
  • Lipid-soluble hormones
  • Water-soluble hormones
• Nuclear receptors


  Lipid-soluble hormones bind to these, which can be located in the cytoplasm or nucleus
• Membrane-bound receptors


  Water-soluble hormones bind to these, which are proteins that extend across the cell membrane
• Pituitary Gland


  • Small gland in brain
  • Controlled by hypothalamus
  • Divided into 2 regions: anterior and posterior
  • Secretes at least 6 hormones
• The anterior pituitary gland synthesizes hormones under the control of the hypothalamus


  Neurons of the hypothalamus secrete releasing hormones that stimulate the production and secretion of a specific hormone, and inhibiting hormones that decrease the secretion of a specific anterior pituitary hormone
• The posterior pituitary gland stores and releases hormones produced by neuroendocrine cells in the hypothalamus


  The two hormones released from the posterior pituitary are antidiuretic hormone (ADH) and oxytocin
• Anterior Pituitary Hormones


  • Growth Hormone
  • Thyroid-Stimulating Hormone (TSH)
  • Gonadotropin Hormone Luteinizing Hormone (LH) for females
• Growth Hormone


  Target tissues: most tissues, Functions: stimulates growth of bones, muscles, and organs, Abnormalities: Too much GH causes giantism, Too little GH causes pituitary dwarfism
• Thyroid-Stimulating Hormone (TSH)


  Target tissues: thyroid gland, Functions: regulates thyroid gland secretions, Abnormalities: Too much TSH, thyroid gland enlarges (goiter), Too little TSH, thyroid gland shrinks
• Posterior pituitary gland


  Stores and releases hormones produced by neuroendocrine cells in the hypothalamus
• Hormones released from the posterior pituitary

  • Antidiuretic hormone (ADH)
  • Oxytocin
• Anterior Pituitary Hormones: Growth Hormone (GH)


  • Target tissues: most tissues
  • Functions: stimulates growth of bones, muscles, and organs
  • Abnormalities: Too much GH causes giantism, Too little GH causes pituitary dwarfism
• Anterior Pituitary Hormones: Thyroid-Stimulating Hormone (TSH)


  • Target tissues: thyroid gland
  • Functions: regulates thyroid gland secretions
  • Abnormalities: Too much TSH, thyroid gland enlarges (goiter), Too little TSH, thyroid gland shrinks
• Anterior Pituitary Hormones: Luteinizing Hormone (LH)


  • For females: Target tissue: ovaries, Function: promotes ovulation and progesterone production
  • For males: Target tissue: testes, Function: production of sperm and testosterone
• Anterior Pituitary Hormones: Follicle-Stimulating Hormone (FSH)


  • For females: Target tissue: follicles in ovaries, Function: follicle maturation and estrogen secretion
  • For males: Target tissue: seminiferous tubules (testes), Function: sperm production
• Anterior Pituitary Hormones: Prolactin


  • Target tissues: mammary glands and ovaries, Functions: milk production
• Anterior Pituitary Hormones


  • Growth Hormone (GH)
  • Thyroid-Stimulating Hormone (TSH)
  • Luteinizing Hormone (LH)
  • Follicle-Stimulating Hormone (FSH)
  • Prolactin
  • Melanocyte Stimulating Hormone (MSH)
  • Adrenocorticotrophic Hormone (ACTH)
• Hormones of the Posterior Pituitary: Antidiuretic Hormone (ADH)

  • Target tissues: kidneys, Functions: conserve water, Abnormalities: Diabetes insipidus - low ADH, kidneys produce large amounts of dilute (watery) urine, can lead to dehydration and thirst
• Hormones of the Posterior Pituitary: Oxytocin


  • Target tissues: uterus, Functions: increases uterine contractions during labor
• Thyroid gland


  One of the largest glands, requires iodine to function, secretes thyroid hormone and calcitonin
• Thyroid Hormones


  • Target tissues: most tissues, Functions: regulates metabolic rates and is needed for growth
• Calcitonin


  • Target tissues: bone and some other tissues, Function: reduces blood calcium level when high
• Hypothyroidism


  • Decreased metabolism, Weight gain, reduced appetite, fatigue, Low temp. and pulse, Dry, cold skin, Myxedema in adults, Cretinism in infants
• Hyperthyroidism


  • Increased metabolism, Weight loss, increased appetite, nervousness, Higher temp. and pulse, Warm, flushed skin, Graves' disease (leads to goiter)