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 Thyroid gland secretes tri and tetra –iodo
thyronine also called as T3 and T4.
 Derived from tyrosine on de-iodination.
 Functions of thyroid hormones.
Necessary for proper functioning of almost all
cells in our body and for biological processes.
Calorigenic effect or thermogenesis.
T4 stimulates RNA synthesis and thereby
protein synthesis.

 Functions of thyroid hormones
I. Increase BMR ( Basal Metabolic Rate )
↑cellular metabolic activity by :
• ↑ size, total membrane surface & number
of mitochondria
• ↑ ATP formation
• ↑ active transport of ions ( Na +, K + )
2.Promote growth & development of the
brain during fetal life and for the first few years
of postnatal life.

Transport of thyroid hormones
 T4 and T3 are transported in blood by binding
to plasma proteins called thyroxine binding
globulin.
 The bound form is biologically inactive.And
FREE form is active.
 Thyroxine binding globulin carries 80% of T4
and 60% of T3.

 TSH secretions are
controlled by
 ‐ Circulating levels of
thyroid hormones.
 ‐ Thyrotropin
releasing hormones.
 Hypothalamic –
pituitary –thyroid
hormone axis is
involved in feed back
control.

 ™Measurement of T4 and T3 by ELISA.
 Hyper thyroidism – both T4 and T3 are
increased and TSH is decreased.
 Hypothyroidism – bothT4 and T3 are
decreased and TSH is increased due to feed
back inhibition.
 When hypothyroidism is due to hypothalamic
or pitutary causes TSH,T4 and T3 are all
decreased
 Normal T4 and T3 values.
 T4 = 5 to 12.5 μgm/dl.
 T3 =70 to200 η gm/dl..

 Estimation of free serum T3 and T4 :
 Free serum T3andT4 in blood not bound to
proteins is independent of changes in(TBG ).
 It provides more reliable diagnosis of thyroid
dysfunction than measurement of total T4and
T3.
 Free T4 = 10 – 27 pmol/l
 Free T3= 3‐ 9 pmol/l

 Serum Thyroid stimulating hormone(TSH)
 Most sensitive ,specific and reliable test of thyroid
status.
 Anterior pitutary TSH release of stored thyroid
hormones.
 ‰Normal values of serum TSH ¾ 2 – 6 micro units/ml.
 ™Clinical interpretation: ‰
 Increased levels are seen in primary hypothyroidism
due to absence of negetaive feed back control on
pitutary. ™
 Decreased levels are seen in Primary(thyroid gland
failure) Secondary (anterior pitutary failure) Tertiary
(hypothalamic failure)

 Thyroxin binding globulin
 Almost all thyroid hormones are bound to
protein, TBG.
 TBG conc affects total plasma conc of T4and T3.
 Normal values of TBG 12‐ 28micro gm/dl.

 Measuring thyroid antibodies helps to
demonstrate presence of auto immune
disorders.
 ‰Thyroid peroxidase antibody {TPOab} and
thyroglobulin antibody {TgAb} - Hashimato’s
thyroiditis and Grave’s disease.
 TSH RECEPTOR ANTIBODY present in
graves disease

Thyroid scanning
 Ultra sound sonography
 CT scan
 MRI scan For the presence of thyroid mass
,cysts and solid tumours.

 Fine needle aspiration
 for this test a small needle is inserted into the
thyrroid gland inorder to get a sample of
thyroid tissue usually from a nodule
 The tissue is then observed under a microscope
to look for any signs of cancer

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