THYROID GLAND
It is an endocrine gland in the lower partof the front & sides of neck.
It has right & left lobes that are joined by isthumus.sometimes a pyramidal lobe maybe present which projects from the isthumus.Sometimes a fibrous or fibromuscular band or levator of the thyroid gland descends from the body of hyoid bone to isthumus or to the pyramidal lobe.
SITUATION & EXTENT:
1)The gland lies against vertebrae c5 c6 c7 & T1.
2)Each lobe extends from middle of thyroid cartilage to 4th or 5th tracheal ring.
CAPSULES OF THYROID GLAND:
1) True capsule-peripheral condensation of connective tissue of gland.
2) false capsule-derived from pretracheal layer of deep cervical fascia.It is thick on the inner surface of the gland & forms suspensory ligament of berry which connects the lobe to cricoid cartilage.
A dense capillary plexus is present deep to the true capsule.Therefore in thyroidectomy, the gland is removed along wit its true capsule to prevent haemorrhage.
RELATIONS:
The lobes are conical in shape & have an apex, base, 3 surfaces & 2 borders.
The superficial surface is covered by the sternothyroid,superior belly of omohyoid,sternohyoid & anterior border of sternocleidomastoid.
Medial surface is related to trachea, oesophagus,inferior constrictor, crico thyroid muscles, external & recurrent laryngeal nerves.
BLOOD SUPPLY:
1)ARERIAL SUPPLY:
(A)Superior thyroid artery(branch of external carotid artery)- it again gives off anterior & posterior branches.
(B) Inferior thyroid artery-branch of thyrocervical trunk
(C) Thyroidea ima artery-arises frm brachiocephalic trunk or arch of aorta. It is seen in 3% of individuals.
VENOUS DRAINAGE:-
(A)Superior thyroid vein
(B)Middle thyroid vein
(C) Inferior thyroid vein
(D) fourth thyroid vein of kocher
The superior,middle & thyroid vein of kocher drain into Internal jugular vein.
The inferior thyroid vein drains into the left brachiocephalic vein.