1. Where is the thyroid located?
    Just inferior to the larynx
  2. What connects the right and left lobes of the thyroid?
    the isthmus
  3. What are the microscopic spherical sacs called that make up most of the thyroid gland?
    thyroid follicles
  4. The wall of each thyroid follicle consist primalrily of cells called ____ ____, most of which extend to the lumer of the follicle.
    follicular cells
  5. The follicular cells produce 2 hormones:
    thyroxine and triiodothyronine (T4 & T3)
  6. Why does T4 have a 4?
    Because it contains 4 atoms of iodine
  7. Why does T3 have a 3?
    Because it has 3 atoms of iodine
  8. What are known as thyroid hormones?
    T3 & T4 together
  9. A few cells called _____ ____ lie between follicles. They produce the hormone _____.
    parafollicular cells

  10. What does calcitonin regulate?
    calcium homeostasis
  11. What is the only gland that stores its secretory product in large quantities?
    the thyroid gland
  12. Most body cells have receptors for what?
    thyroid hormones
  13. What are the 5 actions of the thyroid?
    1. Increase BMR

    2. Stimulate synthesis of additional sodium-potassium pumps (raising body temperature)

    3. Regulate metabolism by stimulating protein synthesis & increase the use of glucose & fatty acids for ATP production; increase lipolysis and enhance cholesterol excretion, reducing blood cholesterol level

    4. Enhance some actions of the catecholamines (epinephrine & NE)

    5. With hGH and insulin accelerate body growth, particularly nervous and skeletal
  14. What controls thyroid hormone secretion?
    TRH & TSH
  15. What is the process of TRH & TSH when stimulating thyroid hormones?
    1. Low levels of T3 & T4 or low metabolic rate stimulate the hypothalamus to secrete TRH

    2. TRH enters the hypophyseal portal veins and flows to the anterior pituitary, where it stimulates thyrotrophs to secrete TSH

    3. TSH stimulates virtually all aspects of thyroid follicular cell activity, including iodide trapping, hormone synthesis and secretion, and growth of the follicular cells

    4. The thyroid follicular cells release T3 & T4 into the blood until the metabolic rate returns to normal

    5. An elevated level of T3 inhibits release of TRH and TSH (negative feedback inhibition)
  16. What are the conditions that increase ATP demand that also increase the secretion of the thyroid hormones?
    cold environment


    high altitude

  17. The hormone produced by the parafollicular cells of the thyroid gland is what?
    calcitonin (CT)
  18. This can decrease the level of calcium in the blood by inhibiting the action of osteoclasts, the cells that break down bone extracellular matrix.
  19. How does CT work when it's blood level is high?
    it lowers the amount of blood calcium and phosphates by inhibiting bone resorption by osteoclasts and by accelerating uptake of calcium and phosphates into bone extracellular matrix.
  20. What is 10x more potent than cuman calcitonin & prescribed to treat osteoporosis?
    miacalcin-a calcitonin extract derived from salmon
Card Set
Endocrine system