Endocrine system

• Endocrine System


  • Controls homeostasis
  • Maintains water balance
  • Controls uterine contractions
  • Controls milk production
  • Regulates ions (calcium, sodium, potassium)
  • Regulates metabolism and growth
  • Regulates heart rate and blood pressure
  • Monitors blood glucose levels
  • Aids the immune system
  • Regulates reproductive functions
• Hormones


  Chemical messengers secreted by endocrine glands or tissues into blood, travel everywhere blood goes, affect only target cells with receptors, may affect very distant organs or cells
• Endocrinology


  Study of endocrine system, diagnosis and treatment of its disorders
• Endocrine glands


  • Ductless, release secretions directly into blood stream
• Exocrine glands


  • Release secretions to tissue by ducts
• Other organs not usually considered endocrine glands

  • e.g., brain and heart, releasing important substances
• Endocrine System


  Chemical signals only, slower to respond and stop, hormones go everywhere, adapts relatively slowly, sometimes widespread effects
• Nervous System


  Chemical and electrical signals, responds and stops quickly, targets specific organ, adapts quickly, usually local effects
• Intracellular signals


  Produced in one part of a cell and move to another part of the same cell
• Intercellular signals


  Released from one cell and bind to receptors on another cell
• Autocrine


  Intracellular signals released by cells and have a local effect on same cell type
• Paracrine


  Intracellular signals released by cells that affect other cell types in close proximity
• Neurotransmitters and neuromodulators


  Intracellular signals secreted by nerve cells
• Pheromones


  Intracellular signals secreted into environment and modify behavior and physiology of other individuals in same species
• Hormones and neurohormones


  Intracellular signals secreted into blood and bind to receptor sites
• Steroid hormones


  • Lipids synthesized from cholesterol, share structure of four organic rings with varied side groups
• Monoamine hormones


  • Small molecules synthesized from amino acids tyrosine and tryptophan
• Peptide hormones


  • Chains from 3 to more than 200 amino acids, considered proteins if > 50 amino acids
• Hormone receptor


  Given hormone fits receptor like a key fits a lock, cell only responds if it has the proper receptors
• Peptide hormones and most monoamines

  Hydrophilic, unable to pass into target cell, bind to receptor at cell surface
• Cyclic AMP


  Made by removing two phosphates from ATP, activates or reactivates cytoplasmic enzymes, leads to various metabolic effects
• Steroid hormones


  Hydrophobic, readily pass into cell, bind receptor associated with DNA, causes gene to be transcribed, specific protein produced, alters metabolism in various ways
• Components of hormones

  • Receptor site: location on a cell where hormone binds (lock)
  • Target tissues: group of cells that respond to specific hormones
  • Specificity: specific hormones bind to specific receptor sites
• How does a hormone work?

  1. Hormones are secreted by endocrine glands directly into bloodstream

  2. Hormones travel to all parts of body

  3. Hormones (key) bind to receptor site (lock) on target tissue

  4. Response occurs
• Types of hormones

  • Water soluble (proteins, peptides, amino acids)
  • Lipid hormones (steroids and eicosanoids)
• Regulation of hormones


  • Blood levels of chemicals
  • Other hormones
  • Nervous system
  • Negative feedback
• Pituitary gland


  Small gland in brain, controlled by hypothalamus, divided into anterior and posterior regions, secretes at least 6 hormones
• Growth hormone (GH)


  Target tissues: most, functions: stimulates growth of bones, muscles, and organs, abnormalities: too much causes giantism, too little causes pituitary dwarfism
• Thyroid-stimulating hormone (TSH)


  Target tissues: thyroid gland, functions: regulates thyroid gland secretions, abnormalities: too much causes thyroid gland enlargement, too little causes thyroid gland shrinkage
• Luteinizing hormone (LH)


  For females: target tissue is ovaries, functions: promotes ovulation and progesterone production, for males: target tissue is testes, functions: sperm production and testosterone
• Follicle-stimulating hormone (FSH)


  For females: target tissue is follicles in ovaries, functions: follicle maturation and estrogen secretion, for males: target tissue is seminiferous tubules in testes, functions: sperm production
• Prolactin


  Target tissues: mammary glands and ovaries, functions: milk production
• Antidiuretic hormone (ADH)


  Target tissues: kidneys, functions: conserve water, abnormalities: diabetes insipidus (low ADH, kidneys produce large amounts of dilute urine, can lead to dehydration and thirst)
• Oxytocin


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


  One of largest glands, requires iodine to function, thyroid hormones regulate metabolic rates and are needed for growth
• Hypothyroidism


  Decreased metabolism, weight gain, reduced appetite, fatigue, low temperature and pulse, dry cold skin, myxedema in adults, cretinism in infants
• Hyperthyroidism


  Increased metabolism, weight loss, increased appetite, nervousness, higher temperature and pulse, warm flushed skin, Graves' disease (leads to goiter)
• Calcitonin


  Target tissues: bones, functions: secreted when blood Ca2+ levels are high
• Parathyroid hormone (PTH)


  Target tissues: bones and kidneys, functions: regulates blood Ca2+ levels (more than calcitonin), if Ca2+ is low then osteoclasts breakdown bone matrix and less Ca2+ is lost in urine, if Ca2+ is high then osteoclasts don't breakdown bone matrix and more Ca2+ is lost in urine
• Adrenal medulla


  Epinephrine/Norepinephrine: target tissues are heart, blood vessels, liver, fat cells, functions: released as part of fight or flight response