endocrine system

• The Endocrine System

  
• Endocrine system


  • Network of hormone-secreting organs that coordinate homeostatic and physiologic processes including reproduction, development, metabolism, growth, and behavior
• How the endocrine system works

  1. Endocrine glands secrete hormones

  2. Hormones travel through circulatory system to target cells

  3. Hormone receptors trigger cellular response

  
• Feedback mechanisms


  • Negative feedback: inhibits a response by reducing the initial stimulus (i.e. epinephrine, cortisol)
  • Positive feedback: reinforces a stimulus to produce an even greater response (i.e. oxytocin, estradiol)
• Autocrine signal


  A chemical signal that affects the very cells that synthesize it

  
• Paracrine signal


  A chemical signal that affects neighboring cells

  
• Endocrine signal


  A chemical signal that affects distant cells outside the organ that secreted it

  
• Testosterone is an example of an autocrine, paracrine, and endocrine signal
• Endocrine glands


  • Hypothalamus
  • Pituitary
  • Adrenal
  • Thyroid
  • Gonads
• Types of hormones


  • Steroid hormones
  • Peptide hormones
  • Amine hormones
• A single hormone can have multiple effects on target cells with different receptors or signal transduction pathways
• Coordination of the endocrine system


  • Negative feedback
  • Positive feedback
• Insulin and glucagon in glucose metabolism

  Example of antagonistic hormones controlling homeostasis via negative feedback

  
• Many important pathways involve multiple hormones in the brain and endocrine glands (H-P-E (G or T or A) system)

  
• H-P-E (G-T-A) system

  1. Hypothalamus receives information and secretes releasing hormones

  2. Pituitary gland receives releasing hormones and secretes tropic hormones

  3. Tropic hormones trigger hormone secretion in endocrine glands

  
• Hormones and their actions


  • FSH/LH release sex hormones from the gonads
  • TSH releases hormones from the thyroid
  • ACTH releases stress hormones
  • Prolactin promotes milk production
  • MSH promotes melanin forming cells
  • GH directs bone growth and triggers release of growth factors

  
• Adrenal hormones: stress response


  • Adrenal gland secretes steroid hormones (cortisol, aldosterone) and epinephrine/norepinephrine to mediate 'fight-or-flight' responses

  
• Gonadal hormones: reproduction, sexual differentiation and behavior


  • Gonads secrete sex hormones (androgens, estrogens, progestins) to mediate secondary sex characteristics and reproductive behavior
• Disorders of endocrine function

  • Hypo/hyperthyroidism
  • Addison's disease
  • Cushing's syndrome
  • Diabetes mellitus
  • Diabetes insipidus
  • Hypopituitarism
  • Gigantism/dwarfism
  • Osteoporosis
  • Hermaphroditism
  • Androgen insensitivity
  • Klinefelter syndrome
  • Many cancers