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Thyroid Gland - Anatomy & Physiology (view source)

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*[[Thyroid Gland - Pathology#Hyperthyroidism|Hyperthyroidism]]

*[[Thyroid Gland - Pathology#Hypothyroidism|Hypothyroidism]]

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==Functional Anatomy (summary)==

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The thyroid gland lies in the neck, in front of the upper part of the trachea. Two types of hormones are produced:

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*Iodine-containing hormones: '''Tri-iodothyronine'''(T3) and '''Thyroxine''' (T4). Thyroid hormones regulate the basal metabolic rate and are important in the regulation of growth of tissues, particularly nervous tissue. Release stimulated by TSH from the pituitary.

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*'''Calcitonin''': Regulates blood calcium levels along with parathyroid hormone. Acts to reduce blood calcium by inhibiting its removal from bone.

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The majority of the gland is derived from a downgrowth of the foetal tongue. The calcitonin producing cells are different and are derived from the fourth branchial pouch.

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[[Image:Normal thyroid.jpg|right|thumb|125px|<small><center>'''Normal Thyroid'''. Courtesy of A. Jefferies</center></small>]]

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The throid gland is divided into follicles which are bounded by a single layer of cuboidal epithelial cells and a basement membrane. Follicles contain a homogenous colloid material called '''thyroglobulin'''. This is a store of thyroid hormones prior to secretion. The thyroid gland is the only endocrine gland to store its hormone in large quantities.

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In the active gland:

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*Colloid is diminished.

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*Epithelial cells are tall and columnar.

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'''Parafollicular''' cells are found in clusters in the interfollicular space. Also known as '''clear''' cells as their cytoplasm doesn't stain with H and E.

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These cells synthesise and secrete calcitonin in response to raised plasma calcium.

==Test yourself with the Thyroid Gland Flashcards==

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[[Category:Endocrine System - Anatomy & Physiology]]

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[[Category:To Do - A&P]]

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