Question

The pathogen of the thyroid is directly transmitted through.................
A. Urine
B. Water
C. Blood
D. Cerebrospinal fluid

Answer 1

Thyroid hormones are present in the blood either bound or unbound to plasma proteins. Importantly, free, unbound thyroid hormones are the only form that has endocrine activity as it can freely diffuse through cellular plasma membranes and thus bind the cytosolic thyroid hormone nuclear receptor.

Complete answer: Thyroid hormones are extremely important and have diverse actions.
1. They act on virtually every cell in the body to alter gene transcription: under- or over-production of these hormones has potent effects. The process of thyroid hormone synthesis is complex. Once inside the follicular cell, iodide is oxidized to active iodine by hydrogen peroxide. This reaction is catalyzed by the heme-containing enzyme thyroid peroxidase (TPO).
2. Iodine is then actively transported across the apical surface of the follicular cell by the same active process that occurs at the basal surface.
3. The themes among the interacting TH metabolic pathways include the influence of nutrient feedback, through nuclear receptor crosstalk and epigenetic modifications of histones, the impact of adrenergic signaling, and local ligand availability.
4. TH action is exerted primarily via the nuclear TR, a member of the superfamily of hormone-responsive nuclear transcription factors that share a similar structure and mechanism of action.
5. The structure of the nuclear receptors, such as TR, includes a zinc finger motif DNA binding domain and a COOH-terminal domain that mediates ligand interactions as well as binding of coactivators and corepressors. The tissue specificity of the TR isoform expression, and the relative expression of each isoform within a tissue, is another pathway of thyroid hormone action specificity in metabolism.
6. Retinoid X receptor (RXR) is best characterized as a heterodimer partner that binds with other nuclear receptors to DNA response elements, but it can also be directly stimulated by ligand and regulate gene expression.
7. The recognition of TR isoform-specific actions has come from animal models of TR gene mutations and inactivation as well as the phenotype of individuals with TR gene mutations.
TR isoform specificity has also been probed by TR isoform-selective agonists.
8. TR isoform-selective actions are likely due to both the timing and location of TR expression as well as subtle different properties between the major receptor isoforms TRα and -β.

So, the correct answer is “Option C ”.

Note: Nuclear receptors play a key role in metabolic regulation and are attractive therapeutic targets for metabolic disorders. A significant limitation of their use, however, is the unintended metabolic consequences of these agents as well as adverse effects at other sites.