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Thyroid S2M1

  1. What is the embryological origin of the thyroid gland
    • It is derived from endoderm from the floor of the pharynx (foramen cecum)
    • It then descends in front of the gut connected to the thyroglossal duct which later disappears
  2. When does the thyroid reach its final destination
    Week 7
  3. The thyroid is composed of
    Thyroid follicles (spherical) which are filled with colloid
  4. What are thyroid follicles lined by
    • Simple epithelium
    • Simple squamous epithelium
    • Simple columnar epithelium
    • Depending on its activity
  5. What is another name for C-cells and what are they derived from
    • "Parafollicular cells"
    • Derived from neural crest cells that migrate to the body of the 4th pharyngeal pouch and eventually to the thyroid gland
  6. Thyroid follicular cells secrete
    Thyroxine (T4) and Triiodothyronine (T3)
  7. Where is T3 and T4 stored
    Colloid in the lumen of the thyroid follicles
  8. Parafollicular cells secrete
    Calcitonin
  9. What effect does calcitonin have
    • It acts on osteoclasts by inhibiting bone resorption, increasing Ca++ absorption, and decreasing Ca++ and PO4- in blood
    • "CalcitonIN keeps Calcium IN bones"
  10. What is the effect of high Ca+
    Increases Calcitonin secretion and decreases PTH secretion
  11. What is the only thyroid cell that has contact with the hormones T3 and T4
    Follicular cells
  12. TSH is secreted from what and has what effect
    • Secreted from the Pituitary gland
    • It binds to receptors on the basal surface of the follicular cells and triggers the synthesis and secretion of T3 and T4
  13. Thyroglobulin (TGB)
    Synthesized in the RER and glycosylated in the golgi, it is then released into the lumen of the thyroid follicular cells via secretory vesicles
  14. How does Iodide get into the cytosol of the follicular cells from the capillaries
    • It is transported from the capillaries on the basal side by Na/I symporters
    • (ATP is required)
  15. Peroxidase has what role on the apical membrane of the follicular cells
    • It oxidizes Iodide to Iodine (I2) which requires the presence of H2O2
  16. Pendrin
    Iodide/Chloride transport in the follicular cells on the apical side
  17. What happens to the iodine in the lumen of the follicular cells
    It binds to tyrosine residues of TGB to form MIT and DIT
  18. What does coupling of one MIT and one DIT form
    T3
  19. What does the joining of two DIT make
    T4
  20. How long can the thyroid store hormones
    Months (in colloid)
  21. MIT
    Monoiodotyrosine
  22. DIT
    Diiodotyrosine
  23. MIT and DIT or unique in that
    They are reused in the cell
  24. T4 makes up about how much of the released hormone in comparison to T3
    80-90%
  25. What happens in the liver to the T4
    It is converted to T3
  26. How is the secretion of Thyroid Hormone controlled
    • By the level of iodine in the blood (low iodine hinders synthesis)
    • By negative feedback (presence of T3 or T4 stops the thyroid from producing more)
  27. Cretinism
    • Results in children with a hyposecretion of thyroid hormones due to an Iodine deficiency
    • Causes retardation and dwarfism
  28. Graves disease
    Results from thyroid hyperfunction due to immunological dysfunction. Antibodies bind TSH receptors in the follicular cells elevating levels of T4 and T3
  29. Why is TSH low in Graves disease
    Because the high levels of T3 and T4 are shutting the off the release of TSH from the Pituitary gland
Author
lancesadams
ID
89524
Card Set
Thyroid S2M1
Description
Micro Anatomy
Updated

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