Pituitary gland thyroid-stimulating hormone-secreting

Thyroid autonomy appears as a solitary toxic nodule or toxic multinodular goitre. In toxic thyroid, the nodule s synthesis and secretion of thyroid hormones is autonomous from the thyroid-stimulating hormone (TSH), which is produced in the pituitary gland. Accordingly TSH is suppressed and the extranodular thyroid tissue is functionally downregulated. Thyroid autonomy occurs frequently in iodine-deficient countries, whereas it is much less common in iodine-sufficient areas. Constitu-tively activating mutations in the TSH receptor and in the Gs a protein are the major molecular aetiology of toxic thyroid nodules. 

A trophic hormone acts on another endocrine gland to stimulate secretion of its hormone. For example, thyrotropin, or thyroid-stimulating hormone (TSH), stimulates the secretion of thyroid hormones. Adrenocorticotropin, or adrenocorticotropic hormone (ACTH), stimulates the adrenal cortex to secrete the hormone cortisol. Both trophic hormones are produced by the pituitary gland in fact, many trophic hormones are secreted by the pituitary. The pituitary gland is sometimes referred to as the "master gland" because its hormones regulate the activity of other endocrine glands. 

Secondary hypothyroidism, or pituitary hypothyroidism, is the consequence of impaired thyroid-stimulating hormone (TSH) secretion and is less common than primary hypothyroidism. It may result from any of the causes of hypopituitarism (e.g., pituitary tumor, postpartum pituitary necrosis, trauma). Patients with secondary hypothyroidism exhibit undetectable or inappropriately low serum TSH concentrations. In secondary hypothyroidism, a normal thyroid gland lacks the normal level of TSH stimulation necessary to synthesize and secrete thyroid hormones. Such patients usually also have impaired secretion of TSH in response to exogenous thyrotropin-releasing hormone (TRH) administration. 

Control of thyroid function via thyroid-pituitary feedback is also discussed in Chapter 37. Briefly, hypothalamic cells secrete thyrotropin-releasing hormone (TRH) (Figure 38-3). TRH is secreted into capillaries of the pituitary portal venous system, and in the pituitary gland, TRH stimulates the synthesis and release of thyrotropin (thyroid-stimulating hormoneTSH). TSH in turn stimulates an adenylyl cyclase-mediated mechanism in the thyroid cell to increase the synthesis and release of T4 and T3. These thyroid hormones act in a negative feedback fashion in the pituitary to block the action of TRH and in the hypothalamus to inhibit the synthesis and secretion of TRH. Other hormones or drugs may also affect the release of TRH or TSH. 

Nerve impulses stimulate the hypothalamus to send specific hormones to the pituitary gland, thus stimulating (or inhibiting) the release of tropic hormones. The anterior pituitary hormones in turn stimulate other endocrine glands (thyroid, adrenals, pancreas) to secrete their characteristic hormones, which in turn stimulate specific target tissues. 

Thyrotropin-releasing hormone is one of several small peptide hormones secreted by the anterior lobe of the pituitary gland. These are the master" hormones that function to stimulate hormone secretion from other endocrine glands. Thyrotropin stimulates the functioning of the thyroid gland. 

TRH stimulates the anterior pituitary gland to release or secrete Thyroid-Stimulating-Hormone (TSH) (also referred to as Thyrotropin on some lab chem. Panels)... 

Correct answer = O. Propylthiouracil blocks the synthesis of the thyroid hormones, but does not affect the uptake of iodide, proteolytic cleavage of thyroglobulin, or the release of hormones from the thyroid gland. The thyroid hormones inhibit the secretion of thyroid-stimulating hormone from the anterior pituitary. ... 

Thyroid-stimulating hormone Posterior pituitary TSH Thyroid gland Secretion of thyroid hormones... 

Thyrotropin, thyroliberin, or thyroid-stimulating hormone (TSH) is a peptide released by the anterior pituitary gland that stimulates the thyroid gland to release thyroxine (Ladram et al., 1994). The release of TSH is triggered by the action of thyrotropin-releasing faetor (TRF), a peptidic substance found in the hypothalamus of the brain and influencing the secretion of glandula thyroidea. 

Thyroid stimulating hormone (TSH) thyro-trophin, a glycoprotein of the anterior pituitary, controls the synthesis and release of thyroid hormone from the gland, and also the uptake of iodide. There is a negative feedback of thyroid hormones on both the hypothalamic secretion of TRH and pituitary secretion of TSH. 

Three possible causes of hypothyroidism are the decreased secretion of thyrotropin-releasing hormone (TRH) by the hypothalamus gland, decreased secretion of thyroid-stimulating hormone (TSH) by the pituitary gland, and decreased secretion of thyroid hormones by the thyroid gland. 

Thyroid-stimulating hormone (TSH)—A polypeptide hormone secreted by the anterior pituitary gland that stimulates iodine uptake and thyroid hormone synthesis. 

In 1922, Smith and Smith (S12) found a substance in bovine pituitary glands which activated the thyroid of hypophysectomized tadpoles. For many years this finding was the basis for the assay of what has come to be called thyroid-stimulating hormone (TSH). The mechanism by which TSH stimulates the thyroid to organify iodine and secrete thyroxine has received much attention in recent years. 

TSH (thyroid stimulating hormone) which acts specifically on the thyroid gland to elicit secretion of thyroid hormones. Disorders of the hypo-thulamie-pituitary-lhyroid axis arc described in detail on pages 80-S5. 

Thyroid-stimulating hormone (thyrotropin) is a glycoprotein (molecular weight, 28,000-30,000 daltons) secreted by the anterior lobe of the pituitary gland that is necessary for the growth and function of the thyroid. A recombinant thyrotropin a useful for the detection and treatment of cancer was approved by the U. S. FDA in November 1998. 

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