Thyroid Flashcards
(54 cards)
C cells are known as?
Parafollicular cells
What do c cells do?
Secrete calcitonin, a peptide hormone
What does c cells cause?
Medullary corcinomas.
A neuroendocrine tumour that comprises ±5% of thyroid cancers,
arising in the C (parafollicular)
cells
Thyroid epithelial cells are also known as?
Thyrocytes
Thyrocytes are organised in what kind of shape?
spherical follicles

Follicular cells secrete?
Thyroid hormone
The thyroid secretes what 3 hormones?
T3, T4 and calcitonin
Differences between T3 and T4?
T4 is secreted in greater amounts than T3. Small amount in reverse T3 form. T3 is more potent than T4.
How is T4 converted to T3?
By a deiodinase enzyme found in many peripheral tissues
How is T3 more potent than T4? (ie greater chemical action)
Binds with a higher affinity to T3 receptors
Name the 3 types of deioninases?
Type 1 Type 2 Type 3
Type 1 deioninases?
Low affinity Converts to T4 to T3. Supply circulating T3
Type 2 deionisases?
High affinity Expressed by glial cells of CNS. Provides T3 even when T4 levels are low.
Type 3 deioniases?
Highly expressed in pregnancy. Role in regulating thyroid hormone inactivation. Convertes T4 to inactive T3
Biosynthesis of Thyroid hormone?
add pic. Iodide in uptake from the blood by thyroid follicular cell. This iodide is excreted to the follicle colloid to be oxidised to be iodine. This iodine is added to thyroglobulin (also excreted by the thyroid follicular cell by exocytosis into follicle colloid). Couple this I2-thyroglobulin and endogenesis back into the thyroid follicular cell. Thyroglobulin lysosomal degradation is the enzyme that degrades the I2-thyroglobulin to T4, T3, MIT & DIT subunits. T3 & T4 are taken up by the blood system.
What is the follicle colloid?
The space surrounding thyroid follicles.
What enzyme is responsible for the iodination and conjugation reactions?
Peroxidase enzymes
Thyroglobulin
Synthesised by thyroid epithelial cells Secreted into the lumen of the follicle.
What pump is used to take up the iodide from the blood?
the sodium-iodide symporter
Na is transported into the follicular cell down its conc gradient while iodide into the cell against its conc. gradient.
Colloid
Colloid is ingested by thyroid epithelial cells by endocytosis. Laden endosomes fuse with lysosomes, which contains enzymes that digest thyroglobulin.
DIT (diodotyrosine)
Intermediate of the biosynthesis of thyroid hormone.
MIT (monoiodotyrosine)
Iodinated amino acid involved in the synthesis of T4 &T3.
What much iodide is ingested & excreted each day?
400micrograms
How much iodide is taken up by the thyroid gland
70-80 micrograms


