Gross anatomy of THE thyroid and parathyroid glands
Transcript of Gross anatomy of THE thyroid and parathyroid glands
GROSS ANATOMY OF THE THYROID AND
PARATHYROID GLANDS
ATIBA, P.M.
THYROID GLAND
• Is a brownish-red,
highly vascular
endocrine organ
located in the lower
part of the neck.
•Extends from C5 to T1
vertebra
LOCATION OF THE GLAND
•Situated on the anterior
side of the neck
•Lies against and around
the larynx and trachea
•Posteriorly, it reaches the
esophagus and carotid
sheath
• Is invested by a thin fibrous
capsule (true capsule);
sends septa into the
substance of the gland
• Also invested (outside
fibrous capsule) by the
pretracheal layer of deep
cervical fascia [false
capsule]
Capsule of the gland
•Has a parenchyma
whose cells are
arranged into follicles.
•These follicles produce
thyroid hormones (tri-
iodothyronine and tetra-
iodothyronine or
thyroxine)
•Weighs 20 – 25 g in man;
Heavier in females than in
males, and increases in
weight during menstruation
and pregnancy
•Consists of a median
isthmus and two lobes
(right and left)
Structure
LOBES
• Is directed upwards and laterally
from the level of the 4th (or 5th)
tracheal ring below to the oblique
line of the thyroid cartilage above
• Has a base and an apex; Apex is
directed upwards
• Has lateral, medial and posterior
surfaces
RELATIONS OF THE THYROID LOBES
• Medially: pharynx, oesophagus,
trachea, larynx, external laryngeal
and recurrent laryngeal nerves
• Laterally: (superficially)
sternohyoid and sternothyroid
• Posteriorly: carotid sheath and its
contents, parathyroid glands,
inferior thyroid artery
ISTHMUS OF THE GLAND
• Median part of thyroid that
connects the two lobes
• Located ventral to the 2nd
and 3rd tracheal cartilages
• Related anteriorly to
sternothyroids,
sternohyoids, anterior
jugular veins and skin
PYRAMIDAL LOBE
• May possess a conical extension
(in 50 % of the population) – the
pyramidal lobe – that projects
towards the hyoid.
• A fibromuscular band- levator of
the thyroid gland, may descend
from the hyoid to the pyramidal
lobe (or isthmus) of the gland.
VASCULAR SUPPLY
• Blood vessels of thyroid are
located largely between its
fibrous capsule and the
pretracheal layer of the deep
fascia of the neck
• Arterial blood comes from
the superior and inferior
thyroid arteries (branches of the
external carotid artery and thyrocervical trunk
resp)
•Additional arterial supply
to thyroid gland may arise
from the thyroidea ima
artery.
•This inconstant unpaired
artery arises from the aortic
arch or brachiocephalic
trunk (present only in 10% of
people)
• Veins of thyroid form a plexus on
the surface of the gland
• From the thyroid venous plexus-
three veins
• Superior
• Middle
• inferior thyroid veins
• The superior and middle thyroid
veins drain into the IJV; inferior
drains into brachiocephalic
•A plexus of lymph vessels also exists in the fibrous
capsule of the gland; this plexus communicates with
those in the interlobular connective tissue
•Lymph vessels, which emerge from the thyroid
gland end in paratracheal, pretracheal,
prelaryngeal and deep cervical nodes
•Nerve fibres reach the gland from the sympathetic
ganglion
•These nerves fibres are however vasomotor and
not secretomotor
CLINICAL ANATOMY
• Thyroglossal cysts
• Ectopic thyroid
• Hyperthyroidism
• Goiter- pathological enlargement of the gland (enlargement
can compress surrounding structures)
• In malignancy- partial thyroidectomy is done and the
posterior aspect of thyroid is preserved becos of parathyroid
glands
Goiter
PARATHYROID GLANDS
•Are minute ovoid yellowish-
brown endocrine organs
•Are located posterior to the
thyroid, two on each side
(superior and inferior), within
the fibrous capsule of thyroid
gland
•Are made up of a
parenchyma that consists
of principal (or chief)
cells.
•These cells produce
parathyroid hormone (control calcium levels in the body)
SUPERIOR PARATHYROID
•Usually located about midway
along the posterior border of
thyroid gland.
•Relatively constant in position
•A derivative of the 4th
pharyngeal pouch; therefore
also called parathyroid IV
INFERIOR PARATHYROID
• Usually located behind and close
to the lower pole of the lobe of
thyroid
• More variable in position; may be
found in mediastinum, close to
thymus.
• Derivative of 3rd pharyngeal
pouch- also called parathyroid III
NEUROVASCULAR SUPPLY
•Arterial supply- inferior
thyroid arteries; Collateral
circulation reaches the gland via
superior thyroid arteries, thyroid ima
artery, and laryngeal, tracheal and
oesophageal arteries.
• Parathyroid veins drain into
the thyroid plexus of veins.
•Lymphatic vessels drain (along with those of the
thyroid gland) into the deep cervical and
paratracheal lymph nodes.
•Nerve fibres reach the gland from the cervical
sympathetic ganglia via the plexus around the
thyroid arteries. [These fibres are vasomotor (not
secretomotor)]
CLINICAL “TITBIT”
• The posterior aspect of the thyroid is usually preserved
during thyroidectomy so as not to damage the
parathyroid
•Damage to parathyroid will lead to hypocalcemia
leading to tetany (severe muscle twitches and cramps).
Without urgent treatment this will result in death because
respiratory muscles will be involved.