Thyroid and Parathyroid Histology Flashcards
What cell type does the Thyroid arise from?
Endoderm
What embryological structure does the thyroid arise from?
Thyroid Diverticulum
What structure connects the Thyroid to the tongue?
Thyroglossal duct
What are the parts of the thyroid?
Pyramidal lobe(old thyroglossal duct)
Left/Right lobe
Isthmus (connects the two lobes)
What are the 3 hormones secreted by the THyroid gland?
T3
T4
Calcitonin
What is the structural and functional subunit of the Thyroid gland?
Thyroid Follicle
full of Colloid (Thyroglobulin, a glycoprotein)
Simple squamous or Cuboidal Epithelium
Surrounded by a cappillary Plexus
What is the purpose of the parafollicular cells?
Synthesize and release calcitonin
Do Not come in contact with the Colloid
What is the function of Calcitonin?
Released when Serum Ca is high
Stop sign for osteoclasts
Lowers Serum Ca back to normal
What is the hormonal release pathway for secretion of Thyroid Hormone?
TRH Thyrotropes(Basophilic Cells) TSH Thyroid T3/T4
Where does TSH act to stimulate secretion of T3/T4?
Acts on receptors on the basal membrane of the Follicular cells.
How is Iodide used in Thyroid Hormone Synthesis?
Active Transport by Na/I Symporter on the Basal Lamina
Oxidized in the Cytosol of the Follicular Cell
Transported into the Lumen where the Thyroglobulin is Iodinated
How is T3/T4 Secreted by the Lysosomal Pathway?
1) Uptake of Colloid by Endocytosis
2) Fuses with Lysosome
3) Digestion by enzymes releases thyroid hormones
4) T3/T4 released into the bloodstream
(Thyroid Stimulating Hormone is Bound to the receptor during the process)
How is T3/T4 Secreted by the Transepithelial Pathway?
Thyroglobulin Endocytosed (megalin receptors) Throglobulin released into the bloodstream while still attached to T3/T4
What is the Pathophysiology of Hyperthyroidism?
Autoantibodies IgG binds to TSH receptors => increased colloid uptake => excessive Thyroid hormones in Circulation
What are the physical findings in Hyperthyroidism?
Exophthalmos Enlarged THyroid (Toxic Goiter)
What causes exopthalmos?
Fibrosis of Rectus muscles
Loose Connective Tissue accumulation behind eyeball
Which Pharyngeal Pouches give rise to the Parathyroid Glands?
3rd Pouch- Inferior PTG
4th Pouch- Superior PTG
WHat cells/tissues does PTH act on?
PTH attaches to osteoblast receptors
Osteoblasts release osteoclast stimulating factor => osteoclasts activated => Ca and Phos released from the bone
Kidney: Conserves Ca
Excretes Phosphate
GI tract: Regulates Vit D formation in kidneys
VitD facilitates Ca abs in the GI
What are the opposing effects of PTH and Calcitonin?
PTH increases low Blood Ca to normal
Calcitonin decreases elevated blood Ca to normal
What are the effects of HYPOparathyroidism?
Hypocalcema => Tetany
What are the effects of HYPERparathyroidism?
Hypercalcemia => Urinary tract stones
