Transcript Managing people in sport organisations: A strategic

Chapter 22
PART IV: Molecular Pathology of Human Disease
Molecular Basis of Diseases of the Endocrine System
Companion site for Molecular Pathology
Author: William B. Coleman and Gregory J. Tsongalis
FIGURE 22.1
The hypothalamus-pituitary-thyroid axis.
Hypothalamic thyrotropin-releasing hormone (TRH) stimulates pituitary thyroid-stimulating hormone (TSH) secretion.
TSH binds to TSH receptors (TSHR) in the thyroid gland (target organ) to trigger thyroid hormone (T3 and T4)
secretion. Thyroid hormones are released into bloodstream and elicit their physiological functions in peripheral cells
through receptor-mediated mechanism. Meanwhile, thyroid hormones inhibit further hypothalamic TRH and pituitary
TSH secretion through negative feedback. A steady circulating level of thyroid hormones is thus achieved. The example
shown reflects the principal mode of regulation of the hypothalamus-pituitary-target organ axis. ⇓ indicates
stimulation, ⊢ indicates inhibition. NIS: sodium iodide symporter; TPO: thyroid peroxidase; TG: thyroglobulin;
MIT: mono-iodotyrosyl; DIT: di-iodotyrosyl.
Companion site for Molecular Pathology
Copyright © 2009 by Academic Press. All rights reserved.
2
FIGURE 22.2
Pathways of adrenal steroidogenesis.
The three classes of adrenal steroids are shown in bold. Enzymes or proteins that cause CAH when
defective are shown in gray boxes. The 17α-hydroxylase and 17,20-lyase activities are encoded by
the same enzyme (CYP17A1).
Companion site for Molecular Pathology
Copyright © 2009 by Academic Press. All rights reserved.
3