anatomyphysiologyblog - GROSS ANATOMY AND HISTOLOGICAL FEATURES OF THYROID GLAND
The thyroid is a highly vascular ductless gland constitute deep inwards the cervix part too overlapped past times the anterior cervix muscles.
Location of the thyroid gland:
It situated inwards front end too at the sides of trachea reverse 5th, 6th, seventh cervical too 1st thoracic vertebrae inwards the cervix region.
Shape of thyroid gland:
It is H-shaped majority too weighs virtually 25 gms.
Coverings of thyroid gland:
It is enclosed past times fibrous capsule (true capsule). It is likewise invested past times the pretracheal layer of cervical fascia (false capsule).
Attachment
Above, pretracheal fascia is attached to the hyoid os too thyroid cartilage on each side. Below, it enters the thoracic cavity too blends amongst fibrous pericardium of heart. The pretracheal fascia is thickened to shape the ligament (of Berry) which connects each lobe of thyroid amongst the cricoids cartilage (of larynx). These attachments of thyroid gland become far movement upwards too downward amongst swallowing.
Presenting parts of Thyroid gland:
It consists of ii lateral lobes too an isthmus connecting them across.
Lateral lobes:
Each lobe is roughly pyramidal. The apex is directed upward too towards the thyroid cartilage too is sandwiched betwixt the inferior constrictor (of pharynx) too sternothyroid muscles.
The superior thyroid artery too external laryngeal nervus are closely related to the apex of the thyroid lobe. The artery lies superficial too nervus passes deep to the apex. This is why the artery is ligated away from the thyroid gland during surgery.
The base of operations extends upwards to fifth or sixth band of the trachea too is related to the inferior thyroid artery too recurrent laryngeal nerve. Near the base of operations of the lateral lobe, the recurrent laryngeal nervus is closely related to inferior thyroid artery too its branches, nervus crossing the artery either anteriorly or posteriorly or may boot the bucket betwixt the branches of artery. Due to this closed proximity, the artery is ligated some distance away laterally to the thyroid gland to avoid the injury to recurrent laryngeal nerve.
Superficial surface is overlapped past times the cervix muscles whereas the deep surface is related amongst the larynx too trachea, throat too oesophagus too parathyroid glands.
In the surgical handling of hyperthyroidism, the posterior share of each lobe of the enlarged gland is normally preserved to protect superior too recurrent laryngeal nerves too parathyroid gland.
In the surgical handling of hyperthyroidism, the posterior share of each lobe of the enlarged gland is normally preserved to protect superior too recurrent laryngeal nerves too parathyroid gland.
Pyramidal lobe of the thyroid gland
In add-on to its normal presenting parts, closed to 50% of the thyroid glands acquaint a pyramidal lobe that varies inwards size. The lobe extends superiorly from the isthmus of thyroid, normally to the left of the median plane. Influenza A virus subtype H5N1 band of connector tissue may connect the apex of the pyramidal lobe to the hyoid bone.
Arterial furnish to thyroid gland:
Following arteries too their branches furnish the thyroid gland:
Superior thyroid artery, a branch of external carotid artery
Inferior thyroid artery, a branch of thyrocervical body of subclavian artery
These arteries prevarication betwixt the truthful capsule too pretracheal layer of deep cervical fascia.
The superior thyroid artery descend to the superior pole of the gland too divides into anterior too posterior branches after piercing the pretracheal fascia. The anterior branch of superior thyroid arterydescends along the anterior edge of thyroid gland too supplies the anterior surface. the anterior branches of correct too left sides anastomose across the midline. The posterior branch of superior thyroid artery descends along the posterior surface of the gland too anastomose amongst the inferior thyroid artery.
The inferior thyroid artery divides into several branches that pierce the pretracheal fascia too furnish the inferior pole (or base) of the gland.
Thyroid gland is likewise supplied by:
Arteria thyroidea ima, if present, branch of arch of aorta or bracheocephalic trunk
Venous drainage of thyroid gland:
It is of import to sympathize that the veins create non accompany the arteries. They arise from the venous plexus which is acquaint deep to the truthful capsule too are drained past times 3 pairs of veins:
superior thyroid veins (drain the superior pole of the gland)
middle thyroid veins (drain the middle of the lobe) and
inferior thyroid veins (drain the inferior pole of the gland)
Superior too middle thyroid veins drain into internal jugular vein whereas the inferior drains by too large into the left bracheocephalic vein.
Lymphatic drainage of thyroid gland:
superior thyroid veins (drain the superior pole of the gland)
middle thyroid veins (drain the middle of the lobe) and
inferior thyroid veins (drain the inferior pole of the gland)
Superior too middle thyroid veins drain into internal jugular vein whereas the inferior drains by too large into the left bracheocephalic vein.
Lymphatic drainage of thyroid gland:
The lymphatic vessels of the thyroid gland run inwards the interlobular connector tissue, normally accompanying the arteries too shape a capsular network of lymphatic vessels. The lymphatic vessels too hence boot the bucket initially to prelaryngeal, pretracheal, too paratracheal lymph nodes, which drain inwards plough to the superior (from the prelaryngeal nodes) too inferior deep cervical nodes (from the pretracheal too paratracheal nodes). Laterally, lymphatic vessels located along the superior thyroid veins boot the bucket conduct to the inferior deep cervical lymph nodes.
The nerves of the thyroid gland are derived from the superior, middle, too inferior cervical sympathetic ganglia. The nervus fibers accomplish the gland through the cardiac too superior too inferior thyroid periarterial plexuses that accompany the thyroid arteries. These fibers are vasomotor too crusade constriction of blood vessels. The secretory business office or endocrine business office of thyroid gland is regulated past times hormones from the pituitary gland.
Structure of Thyroid gland:
The thyroid gland is divided into a number of lobules past times numerous internal septa projecting from the fibrous capsule. Each lobule contains xl to lx thyroid follicles too a stroma inwards which blood vessels too lymphatics ramify.
Thyroid follicle is filled amongst colloid that contains iodinated thyroglobulin every bit storage. The follicle is surrounded past times a unmarried layer of follicular cells. Depending on the reason of activity, the cells are flattened with colloid abundant (resting state) or cuboidal (secretory state) amongst colloid diminished.
REFERENCES:
Following text books are used piece preparing this post (readers are strongly recommended to become through them for to a greater extent than details):
Gray's Anatomy
K. L. Moore's Clinically Oriented Anatomy
R. Snell's Clinical Anatomy
Wheater's Functional Histology