Thyroid
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They thyroid consists of two lobes that are connected by isthmus in front of the _______.
larynx
They thyroid weights about ____g.
15-20
Blood perfusion to the thyroid is…
(5ml/g/min) *highly perfused organ
Adrenergic & ___________ innervation that regulates the tone of blood vessels.
Cholinergic
-The lobes of Thyroid gland: aggregates of spherical follicles * Connection between follicular cells: tight junction
Follicle
• thick gel-like substance in the lumen of follicles • composed primarily of thyroglobulin (10-20%)
Colloid (thyroid globulin main component?) Iodinating glycoprotein
• Produce thyroxine (T4) & triiodo thyronine(T3) • Basal membrane of follicular cells are close to capillary network
Follicular cells
What cells regulate calcitonin in the thyroid?
Parafollicular cells/ C-cells -regulate calcitonin secretion
What are the functional cells of the thyroid?
✦ Follicular cells
What two hormones can activate Vit. D?
PTH and calcitonin (paradox effect)
What is the storage form of thyroid hormone? the active form?
T4- thyroxine* T3-Triiodothyronine* T4 is most abundant in blood but weaker action
increased catecholamine effect? Thyroid hormones
ex: norepinephrine, epinephrine increases CNS, HR, etc.
____ iodine is removed to become T3
5 ‘
Reverse T3? Know what it looks like
Erythrode sick syndrome
Thyroid hormone synthesis: ER —> Apical membrane of follicular cells.
Thyroglobulin
Concentrate iodide from circulation [iodide transporter] - maximum 25-200 times higher than circulation [via basal membrane of FC]
Follicular cells (FC) The sodium/iodide cotransporter, also known as the sodium/iodide symporter, is a protein that in humans is encoded by the SLC5A5 gene. It is a transmembrane glycoprotein with a molecular weight of 87 kDa and 13 transmembrane domains, which transports two sodium cations for each iodide anion into the cell
How is thyroglobulin assembled?
-Iodination of thyroglobulin [thyroid peroxidase] -Product formed: monoidotyrosine (MIT) & diiodotyrosine (DIT)
Coupling reaction of iodinated tyrosine residues -Mediated by thyroid _______ -DIT + MIT = T3 -DIT + DIT = T4 -After iodination, the thyroglobulin molecule is stored as part of the colloid in the lumen of follicle
peroxidase
DIT + MIT = DIT + DIT =
T3, T4
low total T3 and free T3 levels with low or normal T4 and thyroid-stimulating hormone (TSH) levels. -thyroid is NORMAL but the pt appears sick
Euthyroid sick syndrome
Steps of thyroid hormone secretion?
-Start with pinocytosis at the apical membranes of follicular cells -Colloid droplets migrate toward the basal region of the follicular cells -Lysosomes fuse with the colloid droplets Lysosomes hydrolyze the thyroglobulin to its constituent and amino acids -T4 and T3 and the other iodinated amino acids are released into the cytosol -The rest of the amino acids are either released into circulation or recycled for new protein synthesis -The MIT and DIT residues are deiodinated and the iodine is recycled to be incorporated into new TH
True or false: All cells in follicle all make hormone at the same time, and release at the same time.
All of cells forming follicles are are release or building and very synchronized. But not all the follicles in the thyroid gland are synchronized True
Less than ____% of the T4 and T3 in blood is in free form
1
Thyroid hormone secretion: binds to what carrier (plasma) proteins?
➡ thyroid-binding globulin (TBG), transthyretin, albumin, lipoprotein -Protein-bound form of T4 and T3 are large reservoir of performed hormone