12.04.17 Thyroid hormones Flashcards
The thyroid hormones control (3):
– the body’s basal metabolic rate
– the overall metabolism of protein, fat, and carbohydrates
– the sensitivity to catecholamines
Triiodothyronine (T3) and thyroxine (T4) are synthesized from ______
Triiodothyronine (T3) and thyroxine (T4) are synthesized from thyroglobulin
The major form of thyroid hormone in the blood is ___:
- ratio of T4:T3 = _____
- which has longer half-life?
- potency?
- ___% of T4 is converted to T3 in peripheral tissues
The major form of thyroid hormone in the blood is T4:
- ratio of T4:T3 = 20:1
- which has longer half-life? T4
- potency? T3 5-10x more potent than T4
- 25% of T4 is converted to T3 in peripheral tissues
Decarboxylation and deiodination of T3 and T4 produce _____ (T0a) and _____ (T1a).
Decarboxylation and deiodination of T3 and T4 produce thyronamine (T0a) and iodothyronamine (T1a).
Iodine enters the thyroid follicular cell via a _____ channel. It leaves the cell through pendrin and is oxidized by ____, which enables it to iodize _____ which undergoes conjugation, endocytosis, ____ (thyroxine and triiodothyronine) and eventual release into bloodstream.
Iodine enters the thyroid follicular cell via a Na/I symporter channel. It leaves the cell through pendrin and is oxidized by thyroid peroxidase (TPO), which enables it to iodize thyroglobluin which undergoes conjugation, endocytosis, proteolysis (thyroxine and triiodothyronine) and eventual release into bloodstream.
Thyroid stimulating hormone acts directly on ____ cells, increasing (6):
– iodide transport into follicular cells – production of thyroglobulin – iodination of thyroglobulin – endocytosis of iodinated thyroglobulin from the colloid into follicular cells – Proteolysis of iodinated thryoglobulin – exocytosis into the capillaries
The rate of iodine uptake and incorporation into thyroglobulin is influenced by the amount of dietary iodide available
- low iodide levels ____ iodine transport
- high iodide levels ____ iodine transport
The rate of iodine uptake and incorporation into thyroglobulin is influenced by the amount of dietary iodide available
- low iodide levels increase iodine transport
- high iodide levels decrease iodine transport
Major sources of dietary iodine include (4):
– iodized salt (developed to control iodine intake)
– iodated bread (potassium iodate used in flour
preservation and dough leavening process)
– dairy products
– shellfish
Minimum requirement of iodine is ____/day, the US intake is ____/day
Minimum requirement of iodine is 75 micrograms/day, the US intake is 200-500 micrograms/day
Physiological roles of the thyroid hormone include (8):
- Cardiovascular system
- Respiratory system
- Oxygen-carrying capacity
- Oxygen-consumption
- Renal system
- Reproductive system
- Growth and tissue development
- Nervous system
Thyroid receptors belong in the _____ family of receptors. It is constitutively bound to DNA.
- No ligand: ____ gene expression
- With ligand: ____ of gene expression
Thyroid receptors belong in the Retinoid X receptor (RXR) family of receptors. It is constitutively bound to DNA.
- No ligand: No gene expression
- With ligand: Activationof gene expression
Tα1 and Tα2 are splice variants of the ____ gene. Tβ1 and Tβ2 are splice variants of the ____ gene
Tα1 and Tα2 are splice variants of the THRA gene. Tβ1 and Tβ2 are splice variants of the THRB gene.
___, ___, and ___ generally activate transcription when T3 binds. Except in the pituitary, ___ is an activator unbound, but with T3 binding becomes an inhibitor.
Tα1, Tβ1, and Tβ2 generally activate transcription when T3 binds. Except in the pituitary, Tβ2 is an activator unbound, but with T3 binding becomes an inhibitor.
___ does not bind T3/T4 and therefore inhibits
Tα2 does not bind T3/T4 and therefore inhibits
• Tα1: widely expressed, high levels in ____ and ____
muscles
• Tα2: widely expressed, but unable to bind hormone
• Tβ1: predominantly expressed in ___, ___, and ___
• Tβ2: expression primarily in the ___ and ___. Mutations (splicing, receptor) can result in Thyroid resistance disease (Refetoff syndrome)
• Tα1: widely expressed, high levels in skeletal and cardiac
muscles
• Tα2: widely expressed, but unable to bind hormone
• Tβ1: predominantly expressed in brain, kidney, and liver
• Tβ2: expression primarily in the hypothalamus and pituitary
Thyroid resistance disease (Refetoff syndrome)
