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Distinguish between T3 and T4
T3 (triiodothyronine) is the active form of thyroid hormone
T4 (thyroxine) is a prohormone that is converted to T3 by the body.
Why is T3 considered the Major functional thyroid hormone?
T4 is the predominant form of thyroid hormone, but T3 is more potent and biologically active (stimulates a very diverse array of metabolic activities in most tissues)
What is the importance of Iodine?
is necessary for thyroid hormone production
What are the major steps in the Synthesis & Secretion of Thyroid Hormones?
(1) iodide uptake by the thyroid follicular cells
(2) synthesis of thyroglobulin protein
(3) oxidation of iodide to iodine
(4) iodination of thyroglobulin tyrosine residues forming monoiodotyrosine (MIT) and diiodotyrosine (DIT)
(5) coupling of MIT and DIT to form thyroxine (T4) and triiodothyronine (T3)
(6) storage of thyroid hormones within thyroglobulin in the follicular lumen
(7) release of thyroid hormones by endocytosis and lysosomal digestion of thyroglobulin; with the entire process regulated by thyroid-stimulating hormone (TSH) from the pituitary gland.
Thyroid Peroxidase can be defined as…
an important enzyme required for thyroid hormone production
What are the effects of Thyroid-Stimulating Hormone (TSH) on Thyroid Hormone Production and Secretion?
directly stimulates the thyroid gland to produce and secrete thyroid hormones (T3 and T4) essentially acting as the primary regulator of thyroid hormone production within the Hypothalamic-Pituitary-Thyroid (HPT) axis
when blood levels of thyroid hormone drop, the pituitary gland releases more TSH to signal the thyroid to produce more hormone, maintaining a balanced system.
What is the cellular location of the Thyroid Hormone Receptor?
in the nucleus of cells
Thyroid hormone signaling acts on thyroid hormone (TH) receptor to ______
influence target gene expression
What are the Metabolic Actions of thyroid hormones?
T3 stimulates a very diverse array of metabolic activities in most tissues
Increases metabolic rate overall
Increases oxygen consumption & ATP hydrolysis
Leads to increased thermogenesis
What are the Permissive (thyroid hormone needs to be present for another hormone to fully function) Actions of thyroid hormones?
Thyroid hormone dramatically increases the effectiveness of epinephrine in a target cell
Due in large part to its ability to increase the number of cell surface receptors for epinephrine
TH is permissive on epinephrine’s cellular actions
The thyroid hormone acts closely with the growth hormone (GH) for _____
body growth and development
Thyroid Hormones play a particularly important role in _____
early brain structure development
______acts as a critical regulator for the structure and function of the central nervous system (CNS) during embryonic and early postnatal development
The Thyroid Hormone
