The Thyroid Gland Flashcards
what shape are thyroid hormones?
shaped like a butterfly, lies across trachea at base of larynx, one of larger endocrine glands, (15-20g), but neither visible nor palpable in health.
what are the 2 active forms of thyroid hormones?
T3 (triiodothyronine) and T4 (thyroxine).
what are the 2 cell types of thryoid glands>
C (clear) cells
2. Follicular cells
what are the function of C cells
secrete calcitonin (Ca2+ regulating hormone).
what is the function of follicular cells
support thyroid hormone synthesis and surround hollow follicles.
what are thyroid follicles?
spherical structures whose walls are made of follicular cells
what is the centre of thyroid follicles filled with?
colloid = sticky glycoprotein matrix. Contain 2-3 mths supply of TH.
what do follicular cells manufacture?
the enzymes that make thyroid hormones as well as thyroglobulin, a large protein rich in tyrosine residues.
finish the sentence:
the enzymes and thyroglobin are packaged into vesicles and exported from the foliicular cells into the…
colloid
follicular cells actively concentrate …. from the plasma and transport it into the collide
iodide
what happens to the concentrated iodided that is transported into the colloid?
combines with the tyrosine residues to form the thyroid hormones
wht are tyrosine and iodide derived from?
diet
how doess iodide enter the follicular cells from the plasma via?
Na/I transporteer
how is iodide then transported into the colloid?
pendrin transporter
what happens in response to TSH?
portions of the colloid are taken back up into the follicular cell by endocytosis. Within the cells they form vesicles which contain proteolytic enzymes that cut the thyroglobulin to release thyroid hormones.
are T3 and T4 lipid soluble or water soluble?
lipid soluble
what is the significance of T3 and T4 being lipid soluble?
pass across the follicular cell membrane into the plasma where they bind to plasma proteins, mainly thyroxine-binding globulin. Transporter proteins may also be involved in this process as rare mutations in this protein cause major disruption to TH balance.
where do T3 and T4 circulate?
in the plasma
how is the movement of TH from colloid to plasma triggered/controlled?
under the influence of TSH released from the pituitary
what does TSH stimulate?
the follicular cells to endocytose colloidal thyroglobulin. When not stimulated, the thyroid hormones are stored in the colloid.
does thyroxine binding globulin have a high or low affinity for T4?
high which means it releases it slow into the plasma
is it more T3 or T4 that circulates in the form of protein bound T4?
T4
90% of TH binding to TH receptors inside cells is …
T3
the TH receptor has a much higher affinity for
T3 than T4