Receptors for thyroid hormone are located in
Ans. b (Nucleus). (Ref. Ganong Physiology 22nd/pg. Chapter 1 and Figure 1-35)Thyroid hormones enter cells, and T3 binds to thyroid receptors (TR) in the nuclei. T4 can also bind, but not as avidly. The hormone-receptor complex then binds to DNA via zinc fingers and increases or in some cases decreases the expression of a variety of different genes that code for enzymes which regulate cell function. Thus, the nuclear receptors for thyroid hormones are members of the superfamily of hormone-sensitive nuclear transcription factors.There are two human TR genes: an a receptor gene on chromosome 17 and a b receptor gene on chromosome 3. By alternative splicing, each forms at least two different mRNAs and therefore two different receptor proteins. TRb2 is found only in the brain, but TRal, TRa2, and TRbl are widely distributed. TRs bind to DNA as monomers, homodimers, and heterodimers with other nuclear receptors, particularly the retinoid X receptor (RXR).MECHANISM OF ACTION OF STEROID AND THYROID HORMONESTypeCharacteristic HormonesDisease states due to impairment of receptor functionIntracellular ReceptorsTranscription regulatory proteinsGlucocorticoids, mineralocorticoids, estradiol, androgens, progesterone, triiodothyronine, 1,25-dihydroxy vitamin D, retinoic acidTesticular feminization and other androgen resistance syndromes; cortisol resistance; vitamin D-dependent rickets type II; thyroid hormone resistance; estrogen resistanceMembrane receptorsSeven transmembrane domain receptorsLH, TSH, parathyroid hormone, epinephrine, somatostatin, vasopressin,glucagon, angiotensin II, FSH, prostaglandins, serotoninPseudohypoparathyroidism, nephrogenic diabetes insipidus, malepseudohermaphroditism due to mutations of the LH receptor, Jansen's metaphyseal chondrodysplasiaProtein tyrosine kinasesInsulin, insulin-like growth factor- 1, platelet derived growth factor, epidermal growth factor, fibroblast growth factorDiabetes mellitus with profound insulin resistanceGuanylate cyclaseGrowth hormone, prolactin, cytokines, nerve growth factorLaron dwarfismGrowth hormone prolactin familyAtrial natriuretic peptide Also Know:The differentiation of adipocytes requires the action of a nuclear receptor protein--in the same family as the receptors for thyroid hormone, vitamin A, and vitamin D--known as PPAR# Nuclei:# Microtubules:# Active zones:# Clear vesicles:# Granulated vesicles:Contain steroid receptorsAssociated with kinesinContain syntaxinContain acetylcholineContain catecholamines
Cell membrane
Nucleus
Cytoplasm
DNA strands
Endocrinology and Reproduction