Thyroid Pharmacology Flashcards
What are the two classes of hormones released from the thyroid?
T3 (triiodothyronine) and T4 (thyroxine)
Calcitonin
How are thyroid hormones regulated?
- TRH is released from hypothalamus.
- TSH is stimulated by TRH and released from anterior pituitary.
- T3 and T4 exert negative feedback on TSH/TRH
What are the main physiological effects of thyroid hormones?
- Increased basal metabolic rate.
- Sensitization to catecholamines.
- Growth and development.
What is the precursor protein for thyroid hormones?
Thyroglobulin.
What amino acid does thyroglobulin contain?
Tyrosine.
How many iodine can be added to each tyrosine ring?
1: Monoiodine (MIT)
2. Diiodine (DIT)
Which thyroid hormones are composed from MIT/DIT?
2 DIT: T4
1 DIT/1 MIT: T3
What is the predominant thyroid hormone that is released?
Thyroxine (T4)
What hormone causes coupled MIT/DIT to be endocytosed and processed?
TSH.
What occurs in the apical portion of the thyroid follicle?
Iodination and coupling of thyroglobulin.
What occurs in the intracellular portion of the thyroid follicle?
Processing of thyroglobulin after being iodinated and couple (colloid), endocytosis.
What happens in the basolateral side of the thyroid follicle?
Release of T3/T4 into bloodstream.
How does the thyroid gland accumulate iodide from the bloodstream?
Na/I co-transporter (symport)
What is the mechanism of action of thyroid hormones?
T3 is taken up by transmembrane receptors and bind to receptors in the nucleus. This causes the recruitment of RXR, which forms a heterodimer with the hormone receptor. This complex recruits co-activators that enhance transcription of target genes.
What is occurring in thyroid hormone target cells at rest?
Unbound thyroid hormone receptors associate with TRE to recruit co-repressors (weaken gene transcription)
What is hypothyroidism?
Deficient thyroid function.
What is the cause of hypothyroidism?
Iodine deficiency
Hashimoto’s thyroiditis
Defects
Inappropriate hormonal regulation
What is primary hypothyroidism?
Defect in the thyroid function; low T4/T3 but high TSH.
What is secondary hypothyroidism?
Central defect (pituitary or hypothalamus); low T4/T3 low TSH
What is the treatment for hypothyroidism?
Synthetic thyroxine (levothyroxine)
What is hyperthyroidism?
Overactive thyroid function.
What are the most common causes of hyperthyroidism?
Grave’s disease
Hyperplasia of thyroid (excess release)
What is Grave’s disease?
Stimulation of thyroid by anti-TSH receptor antibodies; high T3/T4 and low TSH. Characterized by goiters and bulging eyes.
What is thyroid hyperplasia?
Thyroid adenoma/goiter; high T4/T3 which causes negative feedback on TSH.
