3 thyroid gland final
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Transcript of 3 thyroid gland final
Captain Rishi Pokhrel
THYROID GLAND
Introduction
Unique endocrine glandLocated superficially
Uses raw material – supplied
externally ( Iodine )
Stores the product (2
months)
Rich blood supply 5 ml/g/min
5 l/hr.
0.4% of body weight - 2% of
total blood flow
Introduction – Historical background
Eponymy – Gr. thyreos (Shield)
Goiters were known long
before the thyroid gland itself.
God Bes of ancient Egypt –
features of myxedema
China 2700 B C
Ayurveda 1400 BC –
“galaganda”
Hippocrates (460-337 BC)
“...when glands of the neck
become diseased themselves,
they become tubercular and
produce struma....” (struma –
goiter)
Hippocrates failed to
differentiate between the
thyroid and the cervical glands
Gallen (130-200 AD) described operations on two boys by ignorant physicians who removed tubercular nodes with their fingernails, rendering one boy mute and the other semi-mute.
secretions of the thyroid lubricated the larynx & cartilage ; aphonia was provoked by cutting the laryngeal nerves
Aetios 550 AD : goiter ->
aneurysm
Bronchocele,
elephantiasis of the
throat etc.
• Leonardo Da Vinci is
generally credited as
the first to draw the
thyroid gland as an
anatomical organ in
1508 AD
Andreas Vesalius (1514-1564) correctly described the anatomy of thyroid gland in detail
B. Eustachius (1520-1547) first used the term isthmus
Thomas Warton (1614- 1673) gave the gland its modern name of thyroid
Robert James Graves, 1835 – hyperthyroidism – Grave’s disease
Partial thyroidectomy - P.S. Dessault (1744- 1795) in Paris.
Guillance Dupuytren 1808 - total thyroidectomy for tumor
Ludwig Rehn, 1880, first successful thyroidectomy for exophthalmic goiter.
Thyroxine was identified only in the 19th century
In 1909, Theodor Kocher won Nobel Prize in Medicine "for his work on the physiology, pathology and surgery of the thyroid gland”
Development Starts from 3rd week of
IUL -1st endocrine gland
to develop Proliferation of cells from
caudal end of
Thyroglossal duct -
endoderm PF or C cells –
Ultimibranchial body –
4th/5th pharyngeal pouch
– neural crest cells
Week 3 (day 24)
appears as midline
vesicular structure at
foramen cecum
form a duct like
invagination of ventral
pharyngeal endoderm
grows caudally to become
thyroglossal duct
Week 7 finishes descent along
midline – forms median
isthmus & 2 lateral lobes
2 lateral anlagen develop
from 4th-5th branchial
pouch, which contains
ultimobranchial body
midline and lateral portions
of thyroid fuse
Thyroglossal duct disappears
– remnants: Pyramidal lobe
(50%) and levator muscles
Week 9: cords and plates of follicular cells are formed
Week 10:cords divide into small cellular groups, small follicular
lumina appear
Week 11-12: colloid secretion appears, thyroid becomes functional
Week 14: well developed follicles are lined by follicular cells and
contain thyroglobulin containing colloid in lumina
Week 20: levels of TSH and T4 starts rising
Week 35: TSH & T4 levels = adults
Early growth and development is independent of TSH
Features
Features
Fleshy mass in the neck, in front of
trachea, concealed by strap muscles of
neck
2 symmetrical lobes united at isthmus.
Lobes 5 x 3 X 2 cm; isthmus 1.25 x 1.25
cm
25 – 30 gms in wt. – variable, larger in
females, varies with menstruation and
pregnancy
Features
Lobes – Pear shaped, triangular in
cross section
apex: oblique line of thyroid
cartilage
base: 4-6 tracheal ring
Isthmus flat and square: against 2-
4 tracheal rings
Pyramidal lobe (50%)
Levator Glandulae thyroidae
Coverings Inner true capsule: condensation
of parenchyma
Outer false capsule: formed by
splitting of pretracheal layer of
deep Cx fascia.
Blood vessels ramify under true
capsule
Ligament of berry – condensation
of PTF from false capsule to
cricoid cartilage- RLN runs in it ->
movement of thyroid gland with
larynx
Deep cervical fascia
Relations
Lobes: Δr in cross section – 3 surfaces: ant-lat, med & post
Only posteromedial border is prominent.
Med surface – 2 each; cartilage, muscle, tubes & nerves
Relations
• Upper pole tucked b/w 2 muscles
• Cannot extend sup.
Relations
Para thyroids lie in post.
Surface b/w 2 capsules
Capsule is thinner
posteriorly
Gland enlargement –
extends posteriorly &
inferiorly
Blood Supply
Blood Supply
Venous Drainage
Veins – wide lumen
No valves in lumen
Kocher’s vein - variable
Lymphatic Drainage
Microscopic Structure
Stroma:
– Fibroelastic true
capsule -> septae ->
ill defined lobules ->
Pseudolobulated
– Septae: blood vs,
nerves lymphatics
– Intralobular loose CT
Follicles: arrangement of
cells in hollow spherical or
short cylindrical masses 0.2-
0.9 mm - Structural &
functional units
Filled with gel like substance
- colloid- Thyroglobulin
Simple Principal/Follicular
cells
Parafollicular or ‘C’ cells
Parenchyma
Resting Follicle Active Follicle
Principal/Follicular cells
Nuclei- Spherical, 1-2
nucleoli
Golgi, rER - prominent
Cytoplasm –
basophilic
Apical vacuoles
Microvilli
Thyroglobulin - Stored follicle – iodine trapping and
iodination - reuptake (Scalloped margins) – lysosmes -
broken into T3 & T4 - secreted
– Lie beside follicle
– Enclosed in same BM
but not reaching lumen
– Larger, rounded &
paler
– Nucleus round /oval,
eccentric
– Secretory granules –
Calcitonin (PTH
Antagonist)
Parafollicular or Clear cells or ‘C’ cells (calcitonin)
Phylogeny
• Thyroid gland evolution -> adapt to the terrestrial
ecosystem with less supply of iodine.
• Jellyfish lack thyroid gland
• Endostyle of non-vertebrate chordates -> homologous to
thyroid (Endostyle: longitudinal ciliated groove on ventral
wall of the pharynx – produces mucus to gather food
particles)
• In lampreys, the larval endostyle transforms into adult
thyroid gland during metamorphosis
• Most primitive vertebrates - follicular thyroid gland but non
capsulated
• Thyroid is encapsulated in cartilaginous fish
• In the higher vertebrate forms, the thyroid is a one- or
two-lobed encapsulated structure.
Thyroid hormones
Primary function of the thyroid -
production of T3, T4, and calcitonin
T3 & T4 – essential for normal
growth, development & metabolism
T4 -> T3 by peripheral organs like
liver, kidney, spleen
T3 is 4 - 10 X more active than T4
Hypothalamo – pitutary – thyroid
axis
Physiology
Thyrocytes (follicular cells)
have four functions:
– collect and transport iodine
– they synthesize thyroglobulin
and secrete it into the colloid
– fix iodine to the thyroglobulin
to generate thyroid hormones
– remove the thyroid
hormones from thyroglobulin
and secrete them into the
circulation.
Synthesis of thyroid hormones
Thyroglobulin is synthesized in the rough endoplasmic reticulum and follows the secretory pathway to enter the colloid in the lumen of the thyroid follicle by exocytosis.
Meanwhile, a sodium-iodide (Na/I) symporter pumps iodide (I-) actively into the cell, which previously has crossed the endothelium by largely unknown mechanisms.
This iodide enters the follicular lumen from the cytoplasm by the transporter pendrin, in a purportedly passive manner
In the colloid, iodide (I-) is oxidized to iodine (I0) by an enzyme called thyroid peroxidase.
Iodine (I0) is very reactive and iodinates the thyroglobulin at tyrosyl residues in its protein chain (in total containing approximately 120 tyrosyl residues).
In conjugation, adjacent tyrosyl residues are paired together. The entire complex re-enters the follicular cell by endocytosis. Proteolysis by various proteases liberates thyroxine and
triiodothyronine molecules, which enters the blood by largely unknown mechanisms.
Calcitonin • 32 - aa linear polypeptide - C cells
• Not under control of hypothalamus or pitutary
• Secretion -> Ca2+, gastrin and pentagastrin
• not essential for life – no replacement required
following thyroidectomy unlike parathyroids.
• antagonist to PTH - reduces Ca2+ level
• Inhibits: Ca2+ absorption by intestine, osteoclast
activity in bone & renal tubular cell reabsorption
of Ca2+
• Agonist to PTH -> Inhibits phosphate reabsorption
by the kidney
• Used clinically for Tt of hypercalcemia &
osteoporosis
Applied Anatomy
Congenital thyroid disorders Aberrant thyroid tissue
Lingual thyroid
Thyroglossal cyst 50% close to or just
inferior to body of hyoid
bone
Thyroglossal fistula –
secondary to rupture of
cyst
Hyperthyroidism Vs. thyrotoxicosis
Graves’ disease—an autoimmune disease
involving autoantibody stimulation of TSH
receptors.
Toxic multinodular goiter — nodular
enlargement of the thyroid in the elderly.
Toxic nodule—autonomously functioning
thyroid nodule; most are adenomas
Lymphocytic thyroiditis /Hashimoto’s
thyroiditis—inflammation causes release of
stored hormones (followed by hypothyroid
phase).
Subacute (de Quervain’s) thyroiditis —
thyroiditis associated with a painful goiter.
Hypothyroidism
Myxedema Cretinism
Thyroid lumps
Thyroid cysts.
Nodule of multinodular
goiter.
Follicular adenoma.
Malignancy – 20%
• Papillary
• Follicular
• Medullary – C cells -> PNPS
• Malignant lymphoma
• Anaplastic
Applied anatomy
Thyroidectomy
lobe, subtotal, total
Transverse skin incision 2.5 cm
above jugular notch
Gap b/w ST & SH opened up –
trachea & isthmus exposed
Muscles retracted laterally or
divided at upper ends –
preserve nerve supply from
ansa cervicalis
Later lobes displayed
Plane of cleavage: b/w 2 capsules
Vessels ligated and divided – STA
right at the lower pole; ITA at
some distance from lower pole
During removal of gland
Ligament of berry released – RLN
injury
Wedge shaped areas on post-
medial surface is left behind- PT
Complications
ELN injury – CT paralysis,
hoarseness of voice,
temporary until the
other side takes over
RLN injury – all intrinsic
muscles except CT
paralyzed, no recovery
What’s Your Message?POWERPOINT 2011
DISCUSSION
Nepal Army Institute of Health Sciences