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.