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Download MBBS Anatomy PPT 5 Thyroid Notes

Download MBBS (Bachelor of Medicine, Bachelor of Surgery) Human Anatomy ppt lectures Topic 5 Thyroid Notes. - anatomy ppt free download human anatomy ppt lectures, medicine notes ppt, anatomy handwritten notes pdf, mbbs 1st year anatomy notes pdf download, best anatomy notes pdf, human anatomy notes pdf, anatomy easy notes pdf, anatomy notes online, anatomy short notes, Anatomy ppt, Powerpoint Presentations and lecture notes.

This post was last modified on 05 April 2022




THYROID GLAND DEVELOPMENT

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? The thyroid gland is the first of the body's endocrine

glands to develop, on approximately the 24th day of

gestation

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? It begins its development from a median endodermal

thickening in the floor of the primitive pharynx just

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caudal to the future site of the tuberculum impar


Descent of the Thyroid Gland

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? Thickening forms a downgrowth, thyroid

diverticulum, which grows into the underlying

mesoderm, and as the embryo elongates and the tongue

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grows, the diverticulum descends in front of the neck

and pharyngeal gut

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? The diverticulum is connected to the tongue by a

narrow canal, the thyroglossal duct, which opens in

the tongue via the foramen cecum, which persists as a

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vestigial pit on the tongue

..Cont

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? Diverticulum grows rapidly and forms 2 lobes
? By week 7 of embryonic development, it reaches anterior to

the trachea, having acquired a small median isthmus and 2

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lateral lobes. By then, the thyroglossal duct usually has

disappeared

? A pyramidal lobe of the thyroid may be observed in as many

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as 50% of patients. This lobe represents a persistence of the

inferior end of the thyroglossal duct that has failed to

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obliterate.


? THE THYROID GLAND begins to function at about the end of

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month 3, at which time, the first follicles containing colloid can

be seen

? AT FIRST, THE THYROID PRIMORDIUM is made up of a solid

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mass of entodermal cells


? It later breaks up into a network of epithelial cords or plates by

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invasion of the surrounding mesenchyme

? By week 10, the cords have divided into small cellular groups,

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and a lumen forms in each cellular cluster. The cells then

arrange themselves in a single layer around the lumen

? During week 11, colloid is seen in these follicle structures, and

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even thyroxine can be demonstrated

REMNANTS OF THE THYROGLOSSAL DUCT

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? The normal remains of the thyroglossal duct are the

vestigial foramen cecum (of the tongue) and the

functional pyramidal lobe of the thyroid gland

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Congenital malformations

? THYROGLOSSAL DUCT CYSTS AND SINUSES

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? Cysts can form anywhere along the course of the developing

thyroglossal duct during descent of the developing thyroid

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gland from the tongue

? Remnants of the duct may persist and give rise to cysts in the

tongue or in the midline of the neck, usually below the hyoid

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bone
ACCESSORY THYROID TISSUE

? Very rarely the thyroid fails to descend from the tongue area

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resulting in a lingual thyroid

? Incomplete descent, which is rare, may result in a cervical

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thyroid that is seen in the neck at or just below the hyoid bone

? Accessory thyroid tissue often is fully functional, originates

from remnants of the thyroglossal duct, thus can be found

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anywhere from the level of the tongue to where the thyroid

gland comes to rest in the neck

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Ectopic Thyroid tissue and Agenesis

? Found in thorax in relation to trachea and bronchi or even

oesophagus

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? Believed to arise from endodermal cells displaced during

formation of laryngotracheal tube.

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? Agenesis of the Thyroid
? Failure of development of thyroid gland may also occur