Lecture 17: Thyroid Hormones 1 Flashcards
Thyroid gland: Single layered circular follicles are comprised of
Cuboidal endocrine cell surrounded by basement membrane
Lumen of follicle of Thyroid Gland is made of what material?
Colloid
Thyroid gland: Newly synthesized, stored hormones are attached to what in the lumen of follicle?
Thyroglobulin
What is absorbed into follicular cells under stimulation
Colloidal thyroid hormone
Parafollicular cells (C cells) secrete what
Calcitonin
Thyroxine is
T4
Triiodythyronine is
T3
What is the active thyroid form?
T3
Large amounts of what are required for thyroid hormone synthesis?
Iodine
Synthesis of thyroid hormones is intracellular or extracellular?
Partially both
What is the major hormone secreted, and what is the biologically active thyroid hormone?
T4 = Major hormone
T3 = Biologically active
In order to synthesize thyroid hormones, first need to synthesize protein molecule called
Thyroglobulin
To synthesize thyroglobulin, you need
Tyrosine
Where is thyroglobulin synthesized?
In rough ER + golgi of follicular cells
After thyroglobulin synthesis, it is put into
Follicular lumen
How are thyroid hormones bound?
Using peptide linkages
Iodide is transported from blood into follicular epithelial cells via which transporters?
2Na/I symporter
Iodide is transported across apical membrane into colloid of follicle via ____ and oxidized iodine
Pendrin
What incorporates iodine into tyrosines at specific sites in thyroglobulin
Thyroid peroxidase
The coupling reaction of tyrosine and iodine results in
MIT and DIT
Two DIT molecules =
T4
One DIT + one MIT =
T3
Excessively high levels of dietary iodide will
Suppress activity of 2 Na/1 I pump
Thyroglobulin is stored in follicles as ______ until stimulation for release of thyroid hormones
Colloid
The stimulus for release of thyroid hormones is
Thyroid stimulating hormone
Retrieval of thyroglobulin from follicle lumen into endocrine cell via
Endocytosis
Cell membranes form
Pseudopods
Lysosomes fuse with colloid droplet and release
T3, T4, free MIT, and free DIT
Deiodinase enzyme
Deionizes MIT and DIT to conserve iodide and recycle
Thyrotropin releasing hormone is released from
Hypothalamus
TRH causes release of
Thyroid stimulating hormone from anterior pituitary
TSH causes release of
T4 and T3 from thyroid gland
Negative feedback of T4 and T3 to
Anterior pituitary and hypothalamus
Large circulating pool of
T4
Small pool and short half life
T3
What effects of age and dog breed size have on circulating concentrations?
Higher levels in small breed dogs
Decrease with age
~10% of T4 and T3 is bound to
Thyroxine-binding globulin
Transthryetin
Lower affinity for T4, readily transfers T4 to target cells
TRH is a what kind of hormone
Tripeptide
TSH is what kind of hormone
Glycoprotein hormone with two subunits
