Diorders of thyroid

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Information about Diorders of thyroid
Health & Medicine

Published on March 27, 2014

Author: mprasadnaidu

Source: slideshare.net

Description

Disorders of Thyroid and parathyroid glands

M.Prasad Naidu MSc Medical Biochemistry, Ph.D.Research Scholar

 1. Hyperthyroidism  2. Thyroid Adenoma  3. Grave’s disease

 Causes:  Due to the presence of TSH like substances – proved by RIA studies  The conc of TSH was found to be 0/less in plasma of Hyperthyroidism patients  The TSH like substances are Abs which bind with same membrane receptors of TSH  These substances activate c-AMP system ↑T4  These Abs act for long time (12hrs) (TSH-1hr)  The ↑ of high T4 caused by Abs suppresses TSH production  Usually these Abs are developed b/cos autoimmunity

 Some times – localised tumor develops in Thyroid tissue called Thyroidadenoma  TA secretes large quantities of T4&T3  It is not associated with autoimmunity  As far as this adenoma remains active, the other parts of Thyroid gland will not secrete the hormone.  This is b/cos the hormone from Adenoma ↓ depresses the production of TSH

 Autoimmune disease  Normally TSH combines with surface receptors of thyroid cells  syn of T4  But in GD , the TSH autoAbs (B-TSAB) produced by B-lymphocytes (Plasma cells) activate the TSH-receptors & ↑ secretion of T4

 Intolerance to heat ( due to ↑ BMR)  ↑ sweating ( due to vasodialation)  ↓ body wt ( Fat metabolism)  ↑ motility of GIT  diarrhoea  Muscular weakness  ↑protein catabolism  Nervousness, extreme fatigue, inability to sleep, mild tremor in the hands, psychoneurotic symptoms such as extreme anxiety/worry (stimulation of CNS)  Enlargement of Thyroid gland i.e, Toxic goiter  Exophthalmos: Autoimmune  some degree of protrusion of eye balls – if severe blindness develops due to  i)protrusion of eye ball stretches the optic nerve  Ii) eye lids cannot be closed  dry  infection

 ↓ secretion of Thyroid hormones  Autoimmune disease which causes destruction of Gland  In most patients it starts as the glandular inflammation called – Thyroiditis  Thyroiditis  fibrosis of the gland  Hypothyroiditis Myxedema (adults) Cretinism (Children)

 Due to hypothyroidism in adults  Causes: occurs in severe conditions – complete lack of thyroid hormones  Signs & symptoms:  Swelling of the face  Bagginess under the eyes  Non-pitting type of edema:- when pressed it does not make pits and the edema is hard (accumulation of Pro+cho.SO4 which form hard tissue with ↑ accumulation of fluid)  Atherosclerosis: ↑ cholesterol – blood ↑ bp

 Other general symptoms:  Fatigue & muscular sluggishness  Extreme somnolence ( 14-16 hrs/day)  Menorrhagia & polymenorrhea  ↓ Cordiovascular functions such as ↓heart rate, ↓ force of contraction of heart ↓ crodiac out put , ↓ blood volume  ↑Body wt  Constipation  Mental sluggishness  ↓ hair growth  Scaliness of the skin  Frog like husky voice

 Children  Causes: congenital absence of thyroid gland (genetic disorder or lack of I2 in diet)  Features:  The newborn baby may appear normal at birth (due to supply of T4 from mother)  But after few weeks – starts developing sluggish movements croacking sound while crying  mentally retarded  Skeletal growth is more affected than soft tissues  Tongue becomes so big – affects swallowing & breathing  Stunted growth

CRETINISM DWARFISM Mental retardation Development of Nervous system is normal Diff parts of the body are disaapropriate Proportionate Reproduction system is affected normal

 Enlargement of thyroid gland  Occurs both in hypothyroidism & Hyperthyroidism  Goiter in Hyperthyroidism  Toxic Goiter  Due to tumor of the gland – Size ↑ - ↑ number of hormones secreting cells ↑ hormone level – Toxic Goiter  Goiter in hypothyroidism –non toxic Goiter  Only enlargement of gland – hormone secretion is ↓

 Based on the cause, Non-toxic Goiter is of 2 types  i) Endemic Colloid Goiter:-  Due to lack of I2 – I2 intake <50µg/day  Therefore no formation of hormones  By feed back mechanism, hypothalamus and anterior pituitary are stimulated  This ↑ secretion of TRH and TSH  secretion of TGb Follicles  As there are no hormones to be cleaved, ↑ accumulation in the follicles  Therefore ↑ size of the gland  In Swiss, Alps, Andes, Great region of US and in India – Kashmir Valley Soil does not I2↓  Therefore Food stuffs lack I2 – very common before the introduction of iodized salts

 Enlargement of Thyroid gland occurs even without I2 deficiency  Exact cause not known  These patients are first affected by Thyroiditis which reduce synthesis of Thyroid hormones  Therefore secretion of TSH ↑  ↑ Size of the gland  In some persons the abnormal enzyme system leads to Goiter(due to deficiency of enzymes like peroxidase, iodinase and deiodinase which are required synthesis of T3&T4)

 Goitrogenic Substances: ( Goitrogens)  Eg: Goitrin  Contains antithyroid substances like propylthiouracil  Therefore TSH secretion ↑ enlargement of Thyroid gland  Goitrogens  in turnips, cabbage, soyabeans  The goitrogens become active only during low I2 intake

 Treatment for Hyperthyroidism:-  1. Surgical removal: Thyroidectomy  2. Antithyroid substances: Thiocyanate, thiourylenes, high conc of inorganic iodides  Treatment of hypothyroidism:  Only treatment is administration of Thyroid extract/ ingestion of pure thyroxine ( tablet)

 Drugs which supress the secretion of T3&T4  1. Thiocyanate: the same active pump which transports I- into Thyroid cells, transports thiocyanate also  So thiocyanate competitively inhibits I2 transport  I2 transport is inhibited  ↓ synthesis of Thyroxine

 Thiourea related substances  Eg: Propylthiouracil and methimazole prevent the formation of T4 from iodides and Tyr  This is achieved by blocking peroxidase activity and partly by blocking coupling of MIT & DIT  During the use of these two antithyroid agents even though the synthesis of Thyroid hormone is inhibited , the formation of TGb is not stopped  The deficiency of the hor ↑ TSH secretion ↑ Size Thyroid gland with more secretion of TGb  TGb accumation in gland  enlargement  non- toxic G

 All phases of Thy.activity ↓  ↓ release of Thyroxine  ↓ Size  ↓ blood supply  Therefore iodides are frequently administrated to hyperthyroid patients

 The most accurate diagnostic test is Direct measurement of conc of Free thyroid hormones in the plasma (T3&T4)  Measurement of BMR:-  In Hyperthyroidism, ↑ 30-60%  In hypothyroidism, ↓ 20-40%  The measurement of TRH and TSH:-  In Hyperthyroidism total absence of TRH & TSH (due to –ve feed back mechanism by the ↑level of Thyroid hormones)

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