The Thyroid Gland Flashcards
Label these diagrams of the thyroid gland.
Pyramid= pyramidal lobe
Where are parathyroid glands embedded?
In the thyroid
What supplies the vocal cords?
Left recurrent laryngeal nerve and it runs close to the thyroid gland
Describe the embryology of the thyroid gland.
Midline outpouching from floor of pharynx (originates from base of tongue)
Development of thyroglossal duct
Divides into 2 lobes
Duct disappears leaving foramen caecum
Final position by week 7
Thyroid gland then develops
What is it called when the thyroid fails to develop at all?
thyroid agenesis
- it can also remain in tongue leading to a lingular thyroid
Label this diagram.
What stain is used to check thyroid histology?
H and E stain
What is the small white spaces in this thyroid histology?
Where reactions take place to make thyroid hormone
How does TSH work on the thyroid gland?
TG=> thyroglobulin
TPO=> thyroperoxidase
MIT and DIT=> monoiodotyrosine and diiodotyrosine
Sodium iodide transporter
lysosome break bonds in thyroglobulin holding T3 and T4 so they can released into blood stream
Iodination occurs colloid
What are the thyroid hormones?
Iodothyronines
coupling reactions from T3 and T4
What is the main product of the thyroid gland?
T4= thyroxine
Why is T3 formed and how does T4 turn into T3?
Deiodinated to triiodothyronine (T3), its bioactive form, in target tissues by DEIODINASE ENZYME
Also can deiodinated in a different position to produce reverse T3 (inactive)
T4-> T3 can happen within target tissue
What is T4?
tetraiodothyronine is a prohormone
What is the half life of T3 and T4?
T4 is roughly 7-9 days
T3 is roughly 2 days
How much of circulating T3 is from the thyroid gland?
80% from deiodination of T4
20% from direct thyroidal secretion
What does T3 provide?
T3 provides almost all the thyroid hormone activity in target cells.
How is T3 and T4 transported in the blood?
Mostly bound to plasma proteins
a) thyroid-binding globulin: TBG (70-80%)
b) albumin (10-15%)
c) prealbumin (aka transthyretin)
Only 0.05% T4 and 0.5% T3 is unbound (bioactive components)
What does T3/ T4 do once inside the cell?
First T4 is converted to T3
T3 then enters the nucleus and binds to TR (thyroid hormone receptor) on TRE gene
Leading to altered gene expression
What are the actions of thyroid hormone in babies?
Essential for fetal growth & development, in particular that of the central nervous system
Untreated congenital hypothyroidism: cretinism
TSH measured in new-born infant’s heel-prick test
What is untreated congenital hypothyroidism called?
Untreated congenital (present since birth) hypothyroidism: cretinism
How is TSH measured in a new-born infant?
TSH measured in new-born infant’s heel-prick test