DEVELOPMENT & STRUCTURE

OF THYROID GLAND

DR TATHEER ZAHRA

ASSISTANT PROFESSOR ANATOMY

DEVELOPMENT OF THYROID

Concept of pharyngeal arch

4th week

7th weekAdults

3rd week

DEVELOPMENT OF FOLLICULAR CELLS

7TH WEEK: Solid cord of cells breaks into

network of epithelial cells as invaded by vascular

mesenchyme

10TH WEEK: Cellular groups formation, Lumen

formation

11TH WEEK: Colloid formation

20TH WEEK: level of TSH ↑, Adult levels by 35th

week

HISTOGENESIS OF THYROID

GLAND

DEVELOPMENT OF

PARAFOLLICULAR CELLS

4th or 5th

pharyngeal pouch

Ultimobranchial

body

Neural crest cells

origin

Ultimopharyngeal body / Ultimobranchial body

AGENESIS OF THE

THYROID GLANDDefective development of thyroid gland ~

Congenital hypothyroidism i.e. Cretinism

No central cause related to Hypothalamic-Pituitary

axis

Absence of gland or one of its lobes ~ Rare

anomaly

Thyroid Hemiagenesis ~ Left lobe most commonly

Mutations in the receptors for TSH is involved in

some cases

PYRAMIDAL LOBE

40% population

Usually to the left of

midline

Levator glandulae

thyroideae

Innervated by branch

of external laryngeal

nerve

THYROGLOSSAL DUCT

CYSTSAsymptomatic ~ unless the

lesion become infected

Painless, progressively

enlarging swelling

Appear in childhood,

adolescence or young

adults

Treatment: Surgery with

removal of hyoid bone

POSSIBLE LOCATIONS OF

THYROGLOSSAL CYSTS

THYROGLOSSAL SINUS &

FISTULA

ABERRANT/ ECTOPIC THYROID

GLAND

ACCESSORY THYROID TISSUE

GROSS STRUCTURE OF

THYROID

Only endocrine gland to

store its secretions

Location & extent

Shape

Length: 5 cm

Width: 2.5 cm

Weight: 25-30 g

True Capsule

Pretracheal fascia covering

RELATIONS OF THE LOBES

ANTEROLATERALLY

POSTEROLATERALLY

MEDIALLY

RELATIONS OF THE ISTHMUS

ANTERIORLY

POSTERIORLY

WHY SWELLINGS OF THYROID

GLAND MOVE WITH SWALLOWING?

THYROID GLAND & AIRWAY

ARTERIAL SUPPLY

Superior thyroid

artery (Anterior &

posterior branches)

Inferior thyroid

artery

Stroma richly

vascularized

Vessels lie between

true & false capsule

RELATIONSHIP OF NERVES WITH

THYROID ARTERIES & THEIR DAMAGE

Superior Thyroid Artery Ligation: Close to gland

Inferior Thyroid Artery Ligation: Lateral to gland

INJURY TO THE RECURRENT & NON

RECURRENT LARYNGEAL NERVES

Blood accumulation and serous exudate after the operation ~ Pressure

effects & nerve compression

Non-recurrent laryngeal nerve (due to lack of normal subclavian

artery) 1% incidence ~ Possible hazard in thyroidectomy

A:Weakness of voice

B: Speech not greatly

affected; Hoarseness of

voice; temporary aphonia or

disturbance of phonation

(voice production) and

laryngeal spasm

C: Impaired breathing,

speech lost

D: Greater degree of

paralysis of abductors

E: Dyspnea & stridor; Needs

cricothyroidotomy or

tracheostomy

VENOUS DRAINAGE

LYMPHATIC DRAINAGE

DEEP CERVICAL

NODES

PRELARYNGEAL

PRETRACHEAL

PARATRACHEAL

THORACIC

DUCT

NERVE SUPPLY

SUPERIOR CERVICAL SYMPATHETIC

GANGLIA

MIDDLE CERVICAL SYMPATHETIC

GANGLIA

INFERIOR CERVICAL SYMPATHETIC

GANGLIA

Periarteriolar nervous plexus:Vasomotor not secretomotor

Hypothalamic control of secretion

FUNCTIONS & REGULATION OF

SYNTHESIS OF THYROID HORMONES

ENLARGEMENT OF

THYROID GLAND

PHYSIOLOGICAL(e.g., during

menstruation & pregnancy)

PATHOLOGICAL e.g., GOITER

(HYPOTHYROIDISM/ HYPERTHYROIDISM)

HYPOTHYROIDISM

CONGENITAL HYPOTHYROIDISM/

CRETINISM

IODINE DEFICIENCY GOITER/ ENDEMIC

THYROID

AUTOIMMUNE/ HASHIMOTO’S THYROIDITIS

ADULT HYPOTHYROIDISM/

MYXEDEMA

HYPERTHYROIDISM/ TOXIC

GOITER/ GRAVES’ DISEASE

Exophthalamic goiter

Autoantibodies

Treatment options:

Surgery

Radiotherapy

Radioactive iodine

ingestion

EXTENT & MECHANICAL EFFECTS OF

GOITER

Attachment of sternothyroid muscle

Limits upward extension

No limit to downward expension behind sternum

Enlarges anteriorly, posteriorly, inferiorly, or

laterally

Retrosternal or substernal more common

Compression of trachea ~ Dyspnea

Severe venous compression

SURGICAL APPROACH OF

THYROID GLAND

TRANSVERSE INCISION IN A LOW SKIN CREASE ON THE FRONT OF NECK

VERTICAL DIVISION OF INVESTING FASCIA

RETRACTION / DIVISION OF STERNOHYOID & STERNOTHYROID MUSCLES

DIVISION OF PRETRACHEAL FASCIA TO EXPOSE GLAND PROPER

LOBECTOMY &

ISTHUMUSECTOMY

TOTAL THYROIDECTOMY

NEAR TOTAL & SUBTOTAL

THYROIDECTOMY

SURFACE ANATOMY OF

THYROID GLAND

Extent of gland: C5-T1 Vertebrae

Isthmus: 2nd, 3rd & 4th tracheal rings

MICROSTRUCTURE OF THE

THYROID GLAND

PARENCHYMA

STROMA

3D VIEW OF THYROID

FOLLICLES

FOLLICULAR/ PRINCIPAL

CELLS PARAFOLLICULAR/ C CELLS

PARENCHYMA & STROMA

FOLLICULAR CELLS

PRINCIPAL/ CHIEF CELLS

PARAFOLLICULAR CELLS

C CELLS/ CALCITONIN CELLS

HYPOACTIVE & HYPERACTIVE

VS. EUTHYROID STAGE

Hypoactive stage: Simple squamous

epithelium lined follicle filled with colloid

Hyperactive stage: Simple columnar

epithelium lined follicle with ↓ in colloid

Euthyroid stage: Simple cuboidal

epithelium + colloid

The height of the follicular cells is directly

proportional to the glandular activity.

REFERENCES

The Developing Human, Clinically Oriented Embryology,

By KEITH L. MOORE - Latest Edition

LANGMAN’S Embryology, By T.W.SADLER - Latest

Edition

LAST’S Anatomy Regional & Applied, By CHUMMY S.

SINNATAMBY - Latest Edition

Clinically Oriented Anatomy, By KEITH L. MOORE -

Latest Edition

Clinical Anatomy By Regions, By RICHARD S. SNELL -

Latest Edition

Basic Histology Text & Atlas, By LUIZ CARLOS

JUNQUEIRA & JOSé CARNEIRO - Latest Edition