Endocrinology: Thyroid Gland Hormones Flashcards
What is the action of thyroid hormone on metabolism?
- Increases hepatic gluconeogenesis
- Increases glycogenolysis
- Increases lipolysis
What is the action of thyroid hormone on bone?
- Increases bone turnover
- Increases bone resorption leading to osteopaenia
What is the action of thyroid homrone on blood?
- Increases EPO
- Increases erythropoiesis
- Increases DPG content of erythrocyte
What is the action of thyroid homrone on Beta-adrenrgic receptors?
Increases receptors in:
* Myocardium (leading to positive inotropic and chronotropic effects)
* Skeletal muscles
* Adipose tissue
* Lymphocytes
What is the action of thyroid hormone on superoxide dismutase levels?
Thyroid hormone decreases superoxide dismutase levels
What is the action of thyroid homrone on Na/K/ATPase (in all tiessues except brain, spleen and testis)?
Increases activity
- Increased O2 consumption
- Increased heat production
Where is thyroid hormone stored?
Colloid of follicular cells
Describe the iodination reactions leading to MIT, DIT and subsequently T3 and T4 production:
- I2 absorbed from bloodstream via iodide trapping
- Thyroglobulin synthesis
- Iodination (I2 binds to tyrosine contained in thyroglobulin)
2) 1) I2 + tyrosine = monoiodotyrosine (MIT)
2) I2 + MIT = diodotyrosine (DIT)
Coupling of iodinated residues:
1) MIT + DIT = T3
2) DIT + DIT = T4
What is thyroid hormone bound to in blood and in what proportions?
- Thyroid-binding globulin (TBG) = 70%
- Albumin = 15%
- Pre-albumin (transthyretin) = 15%
Is there more T4 or T3 in blood?
There is 20x more T4 than T3
What is the half life of T4?
7 days
Is T4 or T3 the active component
T3 is the active component
What is the half life of T3?
1 day
Is rT3 active or inactive and what is its half life?
Inactive.
Half life 4h
