Lec 7 - Thyroid Gland Flashcards
thyroid gland structure
2 lobes
(20-30% of pop have a 3rd lobe = pyrimidal lobe)
which cells secrete calcitonin
parafollicular c cells
what is thyroid follicle filled with
thyroglobulin filled
why is thyroid follicle described as dynamic
both shape and size epithelial cells and amount of thyroglobulin changes
what does hypothalamus release to trigger thryoid stimulating hromone
thyrotropin releasing hormone
TRH
where is TSH released from
APG
what does TSH do
acts on thyroid gland = thyroid hromones released
what negatively feedbacks of APG and hypothalamus
T3
what effects TRH release from hypothalamus
- diurnal release
- stresses decrease release
what type of hormone is thyroid stim hormone
glycoprotein hormone
(the one with the differing beta subunit)
what determines the stability and biological activity of TSH
CHO side chains
what cells produce TSH
pituitary thyrotrophs
how do thyrotrophs increase TSH production
by increasing the production of alpha and beta subunits needed to make it
how does high TSH affect thyroid follicle
- inc tg loss from lumen into cells
- inc blood flow
- inc pseudopodia
- cuboid to columnar
how does iodide get into thyroid follicular lumen
passes through 2 membranes
basolateral and apical through the follicular cells
2 transporters for I- in basolateral cell membrane
- Na+/K+ ATPase (increases Na+ on outside)
- sodium iodide symporter (NIS)
(brings iodide back in with Na+)
transporter for iodide in apical cell membrane
pendrin
what enzyme complex iodinates thyroglobulin
thyroid peroxidase (TPO)
= oxidises iodide so it can connect with Tg
what complex is made when plenty of iodide
di-iodotyrosine (DIT)
2 of these make T4
what complex is made when less iodide
monoioidotyrosine
1 of these and a DIT make T3
normal proportion of T4 to T3
90% T4
10% T3
T4 other name
thyroxine
T3 other name
tri-iodothyronine
what pathway does TSH use
- adenylate cyclase = cyclic AMP = protein kinase A
iodine deficiency effect
= derbyshire neck
non-toxic GOITRE
- effect of thyroid gland trying to extract iodine from blood
- lack of iodide means less T3 produced = NO NEGATIVE FEEDBACK to stop TSH
What is thyroid gland lobes connected by
isthmus
