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The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback control over the hypothalamus as well as anterior pituitary, thus controlling the release of both TRH from hypothalamus and TSH from anterior pituitary gland. [2]
Thyroid follicular cells form a simple cuboidal epithelium and are arranged in spherical thyroid follicles surrounding a fluid filled space known as the colloid. The interior space formed by the follicular cells is known as the follicular lumen .
Thyroid hormones act on nearly every cell in the body. They act to increase the basal metabolic rate, affect protein synthesis, help regulate long bone growth (synergy with growth hormone) and neural maturation, and increase the body's sensitivity to catecholamines (such as adrenaline) by permissiveness. [12]
At 20 weeks, the fetus is able to implement feedback mechanisms for the production of thyroid hormones. During fetal development, T 4 is the major thyroid hormone being produced while triiodothyronine (T 3 ) and its inactive derivative, reverse T 3 , are not detected until the third trimester.
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[2] In posterior pituitary we have hormones that control absorption of water and oxytocin. Anterior hypophysis, neurosecretory cells which release hormones. There is a pituitary portal system, with which the hormones are transported. These hormones are prolactin, growth hormone, TSH, adrenocorticotropic hormone, FSH and LH.
The cells of the anterior pituitary express specific G protein-coupled receptors that bind to the neuropeptides, activating intracellular second messenger cascades that produce the release of anterior pituitary hormones. [4] The following is a list of hormones that rely on the hypophyseal portal system to indirectly mediate their function by ...
The thyroid hormones increase the rate of cellular metabolism, and include thyroxine (T4) and triiodothyronine (T3). Secretion is stimulated by the thyroid-stimulating hormone, secreted by the anterior pituitary. When thyroid levels are high, there is negative feedback that decreases the amount of Thyroid-stimulating hormone secreted.