HUBS Endocrine system

• Homeostasis


  • System that keeps a relatively constant internal environment
  • Supports cell function and processes
• Set-point


  The physiological values for a variable, around which natural / normal fluctuations occur
• Normal range


  • Restricted range for a regulated variable, that allows optimal cell function
  • If the variable falls outside the normal range for that person it can cause illness or disorder, regardless of if it's inside the population reference range
• Population reference values


  • Set of values for a regulated variable that is considered to be normal or healthy
  • Based upon test results from a large population of healthy people
  • Tends to be a wider range, than that of any individuals range
  • 95% of people will have a set point within the population reference range
• Negative feedback loop


  1. Sensors - detect deviations from setpoint, send signal to control centre

  2. Control centre - compares deviated value to setpoint, sends signal to effector

  3. Effectors - act to oppose effect of stimulus, thus restoring variable to set-point
• Positive feedback loop


  • Effector amplifies the change in variable
  • Drives a process to completion by amplifying change in a regulated variable
  • Not used for homeostasis
• Endocrine glands and organs

  • Hypothalamus
  • Parathyroid Glands
  • Pituitary Gland
  • Thyroid gland
  • Adrenal Gland
  • Pancreas
• Hormones


  • Chemicals released by endocrine gland cells
  • Travel through blood
  • Bind to receptors on target cell membrane (water soluble) or within receptors in the target cell (fat soluble)
  • Made from amino acids or cholesterol
• Lipid-soluble hormones need carrier proteins to travel in the bloodstream
• Water soluble hormones don't need a carrier protein
• Differences between lipid-soluble and water-soluble hormones

  • Chemical classification
  • Synthesis and storage
  • Transports
  • Receptor location
  • Action mechanism
  • Response and duration
• The effect of a hormone stops when it gets broken down, recycled or excreted in sweat, urine or feces
• Lipid-soluble chemical classification


  • Amines (Thyroid hormones)
  • Steroids
• Water-soluble chemical classification


  • Amines (catecholamines)
  • Peptides & proteins (most proteins are water soluble)
• Thyroid hormones

  • Premade and stored
• Steroids


  • Made as needed, not stored
• Water-soluble hormones


  • All premade and stored until needed
• Lipid-soluble hormones


  • Bound to carrier proteins
• Water-soluble hormones


  • No carrier proteins needed
• Lipid-soluble hormones


  • Intracellular receptors (in nucleus or cytosol)
• Water-soluble hormones


  • Plasma membrane receptors
• Lipid-soluble hormones


  • Stimulate gene transcription to make new proteins
• Water-soluble hormones


  • Activate 2nd messengers for an amplified response (small amount of hormone = big response, from activation of 2nd messengers)
• Lipid-soluble hormones


  • Slower response, longer duration of hours to days
• Water-soluble hormones


  • Faster response, duration lasts only milliseconds to minutes
• Lipid-soluble hormones


  • Thyroid hormone (increases metabolic rate)
  • Cortisol
• Water-soluble hormones


  • Adrenaline
  • Most other hormones