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.
THYROID GLAND DEVELOPMENT
? The thyroid gland is the first of the body's endocrine
glands to develop, on approximately the 24th day of
gestation
? It begins its development from a median endodermal
thickening in the floor of the primitive pharynx just
caudal to the future site of the tuberculum impar
Descent of the Thyroid Gland
? Thickening forms a downgrowth, thyroid
diverticulum, which grows into the underlying
mesoderm, and as the embryo elongates and the tongue
grows, the diverticulum descends in front of the neck
and pharyngeal gut
? 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
vestigial pit on the tongue
..Cont
? 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
lateral lobes. By then, the thyroglossal duct usually has
disappeared
? A pyramidal lobe of the thyroid may be observed in as many
as 50% of patients. This lobe represents a persistence of the
inferior end of the thyroglossal duct that has failed to
obliterate.
? THE THYROID GLAND begins to function at about the end of
month 3, at which time, the first follicles containing colloid can
be seen
? AT FIRST, THE THYROID PRIMORDIUM is made up of a solid
mass of entodermal cells
? It later breaks up into a network of epithelial cords or plates by
invasion of the surrounding mesenchyme
? By week 10, the cords have divided into small cellular groups,
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
even thyroxine can be demonstrated
REMNANTS OF THE THYROGLOSSAL DUCT
? The normal remains of the thyroglossal duct are the
vestigial foramen cecum (of the tongue) and the
functional pyramidal lobe of the thyroid gland
Congenital malformations
? THYROGLOSSAL DUCT CYSTS AND SINUSES
? Cysts can form anywhere along the course of the developing
thyroglossal duct during descent of the developing thyroid
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
bone
ACCESSORY THYROID TISSUE
? Very rarely the thyroid fails to descend from the tongue area
resulting in a lingual thyroid
? Incomplete descent, which is rare, may result in a cervical
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
anywhere from the level of the tongue to where the thyroid
gland comes to rest in the neck
Ectopic Thyroid tissue and Agenesis
? Found in thorax in relation to trachea and bronchi or even
oesophagus
? Believed to arise from endodermal cells displaced during
formation of laryngotracheal tube.
? Agenesis of the Thyroid
? Failure of development of thyroid gland may also occur
This post was last modified on 05 April 2022