2. AT THE END
• EMBRYOLOGY AND ANOMALIES
• SURGICAL ANATOMY
• HISTOLOGY
• THYROID PHYSIOLOGY
• BIOSYNTHESIS OF THYROID HORMONE
• PHYSIOLOGICAL ACTIONS
• REGULATION
• NORMAL RANGE
3. EMBRYOLOGY
• 1st endocrine organ
• 24th day of intra uterine life
• Develops from median Endodermal thyroid diverticulum
(thyroglossal duct)
• Site of origin of thyroid diverticulum is a depression called
foramen caecum
• It grows down into neck and bifucates
• Proliferation of cells of this bifid end gives rise to lobes of
thyroid
• Caudal pharyngeal complex give origin to parafollicular cells
4.
5. ANOMALIES
ANOMALIES OF SHAPE
1. Pyramidal lobe: normal structure arise from the isthmus
2. Isthmus may be absent
3. One of the lobe may be small/ absent
ANOMALIES OF POSITION
1. Lingual thyroid: thyroid may lie under mucosa of dorsum of
the tongue and may form swelling that may lead on to
dysphagia
2. Intralingual thyroid
3. Suprahyoid thyroid
4. Infrahyoid thyroid
5. Intra thoracic thyroid
6.
7. ECTOPIC THYROID TISSUE
Small masses of thyroid tissue may present at abnormal
sites.
Like larynx, oesophagus,pons, pleura, pericardium, &
ovaries
REMENANTS OF THYROGLOSSAL DUCT
Thyroglossl cyst: anywhere along the course of the
duct.form fistulas in neck
Thyroglossal fistula
Note: In surgical removal of thyroiglossal cyst and fistula it
is important to remove all remanants of thyroglossal duct.
8.
9. SURGICAL ANATOMY
• Weight= 20-25g
• Shield like endocrine gland
• Right and left lobes connected by isthmus
Situation
• Gland lies against C5 to T1 vertebrae
• Each lobe – oblique line on thyroid cartilage to 4th or
5th tracheal ring
• Isthmus extend from 2nd to 4th tracheal ring
10.
11.
12. CAPSULE OF THYROID
• True capsule – peripheral condensation of connective
tissue of the gland
Applied anatomy: a dense capillary plexus is present deep
to the true capsule so to avoid hemorrhage during surgery
the thyroid is removed along with the true capsule
• False capsule- from pretracheal layer of deep cervical
fascia
Applied anatomy :false capsule forms the suspensory
ligament of berry which connects lobe to cricoid cartilage.
That’s why thyroid moves with larynx in deglutition.
13. PARTS AND RELATIONS
• APEX: sup thyroid artery and ext laryngeal nerve
• BASE: inf thyroid artery and RLN
• LATERAL SURFACE : sternohyoid
sup belly of omohyoid
sternothyroid
ant border of SCM
• MEDIAL SURFACE:
2 TUBES - trachea , oesophagus
2 muscles –cricothyroid , inf constrictor
2 nerves- ext laryngeal nerve & RLN
15. • ANTERIOR BORDER: ant branch of sup thyroid
artery
• POSTERIOR BORDER:
1.inf thyroid artery
2.anastamosis b/w post branch of
3.sup thyroid artery and ascending
branch of inf thyroid artery
4.parathyroir gland
• ISTHMUS
ant surface: Rt & Lt SCM
Ant jugular veins
fascia & skin
post surface: 2nd to 4th tracheal rings
19. • SUPERIOR THYROID ARTERY
1. First anterior branch of external carotid artery.
2. Runs downwards and forwards in relation with
external laryngeal nerve.
3. Pierce the pretracheal fascia to reach the upper pole
of the lobe where the nerve deviates medially.
4. Divides into anterior and posterior branches
20. • INFERIOR THYROID ARTERY
1. branch of thyrocervical trunk
2. Runs upwards then medially and finally downwards
to reach lower pole of the gland
3. Terminal part is intimately related to the RLN
while proximal part is away from the nerve
1. Divides into 4-5 glandular branches, one ascending
branch anastamose with post branch of sup thyroid
artery
2. Thyroid also supplied by thyroidea ima artery in 3%
of individuals which arises from brachiocephalic
trunk / directly from aorta
22. LYMPHATIC DRAINAGE
• Lymph channels passes to
delphian nodes and
pretracheal nodes (level 6)
• From there to deep
cervical nodes(level
2,3,4,5)
• And mediastinal group of
nodes (level7)
23. NERVE SUPPLY
• Mainly from middle cervical ganglion and partly
from superior and inferior cervical ganglia
24. HISTOLOGY
• FOLLICULAR CELLS - lining the follicles and
secrete T3 & T4 . During active phase lining of
follicles is columnar while in resting phase it is
cuboidal . Follicles contain colloid
• PARAFOLLICULAR CELLS/ C CELLS- seen b/w
the follicles . Secrete calcitonin which promotes
hypocalcemia and calcium deposition in bones.
These effects are opposite to parathormone
25.
26. THYROID PHYSIOLOGY
• Thyroid follicles secretes colloid which contain
thyroglobulin and thyroid hormones
• About 93%of metabolically active hormones secreted by
the thyroid gland are thyroxine (T4)and 7%
triiodothyronine(T3) .
• Almost all thyroxine is converted into T3 in the tissues
• T3 is four times as potent as thyroxine but it is present in
blood in much smalle quantities and for a shorter
duration.
27. • Iodine is the raw material for thyroid hormone
synthesis
• Ingested iodides are absorbed from GIT into blood
• reduced intake of iodine cause endemic goitre
• Thyroglobulin is bounded to thyroid hormone till it is
secreted into blood after which ingested back into the
colloid
• Thyroid peroxidase(TPO) catalases the oxidation of
iodine and its absorbtion
• Immunoglobulin against TSH receptor or TPO
antibody is found in Hashimotos
28. BIOSYNTHESIS
• IODINE TRAPPING
• OXIDATION OF THE IONINE ION
• ORGANIFICATION
• COUPLING OF IODOTYROSINE RESIDUES
• RELEASE OF T3 AND T4 INTO BLOOD
29. FORMATION OF THYROGLOBULIN
• Thyroglobulin a large glycoprotien synthsised by th
ER and golgi bodies secreted into the follicles by
thyroid cells
• Thyroglobulin = 70 tyrosine amino acids
• Tyrosin are the major substrates that combine with
iodine to form thyroid hormones
30. IODINE TRAPPING
• The process of concentrating iodide in the cells is called iodine
trapping
• Transport of iodine from blood to thyroid cells and follicles
• With the help of sodium iodide symporter
• co transports one iodine along with two sodium ions across
plasma membrane into cells
• Energy = Na-K ATPase
• APPLICATION: Thiocyanates reduces rate of iodine trapping
31. OXIDATION OF IODIDE ION
• Conversion of iodide into iodine
• So that it directly combine with tyrosine amino
acid
• Promoted by enzyme peroxidase
• APPLICATION: propylthiouracil block
peroxidase enzyme
32. ORGANIFICATION
• Binding of iodine with thyroglobulin molecule
• To form Monoiodotyrosine and diiodotyrosine
• APPLICATION: methimazole partly blocks
coupling
33. COUPLING REACTION
• Immediately after formation of monotyrosine and
diiodotyrosine during the next few minutes , hours ,
even days more of tyrosine residues become coupled
with one another
• Major product = tyroxine (2 molecules of
diiodotyrosine)
• One molecule of monoiodotyrosine coupled with
one molecule of diiodotyrosine= triiodotyrosine
• APPLICATION: blocked by carbimazole
34. STORAGE
• Able to store large amount of hormone in such a
way that to meet the normal requirements for 2-
3months
• Therefore when synthesis of thyroid hormone
ceases the physiological effects of deficiancy are
not obsrved for several months
• Each thyroglobuline contain 300 thyroxine and
few amount of triiodotyrosine
35. RELEASE OF THYROID HORMONE
• Thyroxine and triodothyrosine are cleaved from thyroglobulin
and released into blood
• Thyroid cells extend a pseudopodium around a small portion of
colloid to form pinocytic vesicles
• Pinocyte enters thyroid cells and fuse with lysosomes then
digest thyroglobulin
• Free triiodotyrosin and thyroxine are released into cells
• T3 and T4 diffuse out of thyroid cells into surrounding
capillaries
• APPLICATION: high concentration of iodine shuts down
endocytosis of colloid
36. PHYSIOLOGICAL ACTIONS
SITE ACTIONS
CVS Increase CO,HR & force of contraction
RESPIRATORY SYSTEM Increase rate of respiration
GIT Increase motility
CNS Increase rapidity of cerebration
MUSCULOSKELETAL SYSTEM Excitation and more---weaknes
ENDOCRINE Increase activity of all glands
BODY WEIGHT Decrease
METABOLISM Glycolysis,glyconeogenesis,increased
insulin secretion, lipolysis, incresed BMR
, increased vitamin req
37. REGULATION
PITUITARY THYROID AXIS
• Synthesis and liberation of thyroid hormone is
controlled by thyroid-stimulating hormone from the
anterior pituitary.
• Secretion of TSH depends on level of circulating
thyroid hormones(negative feedback mech)
• Regulation of TSH is by the action of thyrotropin
releasing hormone produced by hypothalamus
39. REFERENCE
• BAILEY & LOVE’S SHORT PRACTICE OF
SURGERY
• NETTER’S ATLAS OF HUMAN ANATOMY
• CUNNINGHAM’S MANUAL OF PRACTICAL
ANATOMY
• HUMAN EMBRYOLOGY INDERBIR SINGH
• BD CHOURASIA’ HUMAN ANATOMY
• GUYTON & HALL TEXTBOOK OF MEDICAL
PHYSIOLOGY
• VASUDEVAN BIOCHEMISTRY
