Download 15. thyroid2010-10-01 03:41779 KB

Thyroid gland
Structure : it is the largest
endocrine gland in the body. It has
butterfly shape. It consists of 2 lateral
( right & left ) lobes connected by a
narrow isthmus.
Capsule : it is surrounded by :
1-a sheath derived from pretracheal layer
of deep cervical fascia. this sheath
attaches the gland to larynx and trachea,
so it is responsible for movement of gland
with lartnx up & down during deglutition.
2-Fibrous capsule : is firmly attached to
the gland.
Each lobe : is pear shaped,
its apex is directed upward as far as the
oblique line/ on lamina / of thyroid
cartilage, while its base lies at the level of
5 or 6th tracheal ring.
Thyroid gland
Isthmus :
 It lies in the midline in front of
2,3, and 4th tracheal rings.
 A pyramidal lobe is often
projects upwards from isthmus,
usually to left of midline. It is
connected to the hyoid bone by
a fibromuscular band called
levator glandulae thyroidae
(remnant of thyroglossal duct in
embryo). This band may be
absent.
Relations of Lobes of
Anterolaterally :
Thyroid Gland : sternothyroid, sternohyoid, superior
belly of omohyoid, anterior border of
sternocleidomastoid.
Postrolaterally : carotid
sheath (common carotid artery +
internal jugular vein + vagus nerve).
Medially : larynx + trachea,
pharynx + esophagus, recurrent
laryngeal nerve, cricothyroid muscle
+ its nerve supply, the external
laryngeal nerve.
Cross section of the neck at level
of 6th cervical vertebra.
Posteriorly : the posterior
border of each lobe is related to
superior & inferior parathyroid
glands + anastomosis between
superior & inferior thyroid arteries.
Relations of Isthmus of
Thyroid Gland :
Anteriorly : skin, fascia,
anterior jugular veins,
sternohyoids & sternothyroids.
Posteriorly : 2,3,and 4th
tracheal rings.
N.B : superior thyroid arteries
anastomose along its upper
border.
Arteries of thyroid gland
Superior thyroid artery : a branch of
Anterior surface
external carotid artery, descends to upper pole
of each lobe.
-it is accompanied by superior thyroid vein +
external laryngeal N.
-it divides into anterior & posterior branches.
The anterior anastomoses with its fellow of
opposite side on the upper border of the
isthmus, and the posterior one descends on
posterior surface to anastomose with inferior
thyroid artery.
Inferior thyroid artery : a branch of
thyrocervical trunk from 1st part of subclavian A.
-It turns medially and downward then, upward
to posterior border of gland.
-it is accompanied by recurrent laryngeal nerve.
Thyroidea ima artery : if present, may
Posterior surface
arise from brachiocephalic artery or arch of
aorta. It ascends in front of trachea to the
isthmus.
Veins and lymph drainage of
thyroid gland :
Superior thyroid vein :
drains into internal jugular vein.
Middle thyroid vein :
drains into internal jugular vein.
Inferior thyroid vein :
receives its tributaries from
isthmus & lower poles of gland
and descend in front of trachea
to drain into left brachio-cephalic
vein in the thorax.
The lymph from thyroid
gland drains mainly into upper &
lower deep cervical L.Ns. (along
I.J.V)- Few into paratracheal
L.Ns.(along side of trachea).
Parathyroid glands
They are 2 pairs (2 superior + 2 inferior)
of small endocrine glands embedded in
the posterior aspect of the lobes of thyroid
gland.
Superior parathyroid : lies at the
middle of posterior surface of thyroid, they
are more constant in position.
Inferior parathyroid : lies near base
of thyroid gland.
They lie within the fascial sheath, /
embedded in the posterior wall of fibrous
capsule.
Arterial supply : inferior thyroid
vessels.
Lymph drainage : as thyroid gland.
Cervical part of Trachea
It is a mobile cartilaginous &
membranous tube starting at the
level of cricoid cartilage of larynx
opposite 6th cervical vertebra.
It ends at the level of disc between
4th & 5th thoracic vertebrae opposite
the sternal angle.
Relations :
Anteriorly :
-isthmus of thyroid (in front of 2nd ,3rd
,and 4th rings) + inferior thyroid vein +
thyroidea ima artery + jugular arch.
-sterno thyroid + sternohyoid muscles +
skin & fascia.
Posteriorly : recurrent laryngeal
nerves + esophagus + vertebral column.
Laterally : lobes of thyroid gland
(down as far as 5th or 6th ring ) + carotid
sheath.
Blood supply : inferior thyroid
vessels.
Lymph drainage : pretracheal +
paratracheal L.Ns.
Nerve supply : vagus & recurrent
laryngeal N. + sympathetic trunks.
Cervical part of esophagus &
It is a muscular tube about 25 cm long
its relations :
extending from pharynx to stomach.
It begins at the level of cricoid cartilage
opposite 6th cervical vertebra, and ends
to join the stomach in the abdomen.
Anteriorly : trachea, R.L.N. in
groove between trachea & esophagus.
Posteriorly : prevertebral layer of
deep cervical fascia, longus coli, and
vertebral column.
Laterally : lobe of thyroid gland +
carotid sheath.
Blood supply : inferior thyroid
vessels.
Lymph drainage : deep cervical
L.Ns.
Nerve supply : recurrent L.N. +
sympathetic trunks.