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Thyroid gland and its disorders
- 2. PRESENTED BY MALAIKA TARIQ PRESENTEDTO DR MAHNOOR KHAN TOPIC TO DISCUSS THYROID GLAND
- 3. THYROID GLAND INTRODUCTION HISTOLOGY HORMONES SYNTHESIS ,STORAGE , RELEASE FUNCTIONS DISORDERS TREATMENT DIAGNOSTIC TESTS
- 4. INTRODUCTION • An endocrinegland , at the root of neck on either side of trachea. • Two lobes connected by isthmus HISTOLOGY • Composed of large number of closed follicles , lined with follicular cells , in between are present parafollicular cells. • Follicular cells secrete thyroglobulin( colloidal substance)which fills follicular cavity and also secretes T4 and T3 . • Both T4 and T3 are derivatives of amino acid tyrosine.
- 5. HORMONES • Secretes 3hormones :- I. Tetraiodothyronine or ( thyroxine ) T4 ------90% of secretion II. Tri-iodothyronine or T3 -------9% to 10% of secretion III. Calcitonin • Strength of T3 is four times more than T4 but duration of T4 action is four time more than T3 action .WHY??? Reason is less affinity of T3 for plasma protein , combines loosely with them so released quickly while T4 binds strongly and is released slowly. • Degradation of thyroid hormones occur in kidney , liver and muscles. • Synthesis takes place in thyroglobulin , tyrosine and iodine are essential .
- 6. STAGES OF SYNTHESISOF THYROID HORMONES Synthesis occurs in 6 stages 1) Thyroglobulin synthesis:- ER and Golgi apparatus in follicular cells synthesize and secrete thyroglobulin .After synthesis, it stores in follicles . 2) Iodide trapping:- Iodide is actively transported from blood to follicular cells , against EC gradient ,along with Na+ through Na-iodide symport pump. 3) Oxidation of iodide:- Iodide oxidizes to iodine inside follicular cells in presence of thyroid peroxidase because only iodine combines with tyrosine to form hormone.
- 7. 4 ) Transportof iodine to follicular cavity:- Transported from follicular cells to follicular cavity through iodide –chloride pump called pendrin. 5 ) Iodination of tyrosine :- Iodine binds with thyroglobulin, process called organification . Iodine combines with tyrosine in thyroglobulin , process called iodination .Iodination of tyrosine occurs in different stages: tyrosine first transform to mono-iodothyronine (MIT) and later into tri-iodothyronine (DIT). 6 ) Coupling reaction :- the coupling reaction in different configuration, gives rise to different thyroid hormones.
- 9. STORAGE OF HORMONES •Can be stored up to 4 months, remains in form of vesicles in thyroglobulin. • Only endocrine gland which stores its hormones for long periods, so sign and symptoms of deficiency don’t appear before 4 months. RELEASE FROM THYROID GLAND • Not released in blood directly, hormones are first cleaved from thyroglobulin and then released. • Only T3 and T4 are released into blood stream. MIT and DIT are not released in blood stream, they are deiodinated by enzyme . During congenital absence of enzyme, MIT and DIT are secreted in urine and iodine deficiency develops.
- 10. FUNCTIONS OF THYROIDGLAND • Increases basal metabolic rate(BMR) by increasing O2 consumption except in brain , retina, spleen, testes and lungs. • Increase synthesis of protein in cells ,and cardiovascular activity and carbohydrates metabolism. • Decrease fat storage by mobilizing from adipose tissue and fat depots , increase the fatty acid level in blood. • Decreases cholesterol , phospholipids and triglycerides level in plasma. In hyposecretion of T4, cholesterol level increase ,results in atherosclerosis.
- 11. • Increase heatproduction in body, called thyroid hormone-induced thermogenesis • Increase growth in children, promote brain development in fetal life, deficiency leads to mental retardation . • Decrease body weight, accelerate erythropoietic activity .polycythemia is common in hyperthyroidism. • Increase GIT activity ,hypersecretion cause diarrhea, hypo-- cause constipation. • Maintain normal sleep, hyposecretion cause somnolence . • Affect muscular activity, hypersecretion cause thyrotoxic myopathy and tremors.
- 12. • Increase formationof many enzymes, vitamins are essential. vitamin deficiency is possible during hyposecretion of T4. • Essential for normal sexual function. In males , hyposecretion cause loss of libido and hypersecretion cause impotence .In women, hypersecretion cause oligomenorrhea and amenorrhea, hyposecretion cause polymenorrhea and menorrhagia.
- 13. DISORDERS OF THYROIDGLAND HYPERTHYROIDISM Increased secretion of thyroid gland .Caused by Graves disease and thyroid adenom GRAVES’ DISEASE :- Autoimmune disease ,most common cause of hyperthyroidism B-Lymphocytes produce thyroid stimulating autoantibodies (TBAbe).these antibiotics act as TSH by binding with membrane receptors and activating cAMP systems of thyroid follicular cells , results in hyperthyroidism. THYROID ADENOMA :- sometimes, localized tumor develops in thyroid tissues and secretes large quantity of thyroid hormones. Not associated with autoimmunity, the hormone secreted from adenoma depresses the TSH production.
- 14. Exophthalmos :- • Mostbut not all hyperthyroid patient develops Exophthalmos (bulging of eyes) • Caused due to swelling of retro-orbital tissues and degenerative changes in extraocular muscles. • Leads to blindness due to stretch and damage to optic nerve and due to constant exposure to atmosphere cause dryness ,infection and irritation.
- 15. HYPOTHYROIDISM Decreased secretion ofthyroid hormone ,leads to myxedema in adults and cretinism in children. MYXEDEMA :- edematous appearance. Caused due to thyroid gland , genetic disorder or iodine deficiency .Common cause is autoimmune disease called hashimoto’s thyroiditis,common in middle aged Women. Sign and symptoms includes features like:- Swelling of face, bagginess under eyes ,Non- Pitting type of edema , atherosclerosis.
- 16. CRETINISM :- Occursdue to congenital absence of thyroid gland, genetical disorder , or lack of iodine Features of cretinism include babies with sluggish movements, croaking sound, mental retardness. skeleton growth is more affected than soft tissue. big tongue with dripping saliva.
- 17. SIGN AND SYMPTOMSOF HYPERTHYROIDISM AND HYPOTHYROIDISM
- 18. GOITER Means enlargement ofthyroid gland ,Occurs both in hypothyroidism and hyperthyroidism. Goiter in hyperthyroidism ---- Toxic goiter :- Enlarged thyroid gland with increased hormone secretion, caused by thyroid tumor. Goiter in hypothyroidism ---- nontoxic goiter :- Enlarged thyroid gland without increased thyroid hormone secretion.
- 19. Based on cause,nontoxic goiter classified into two types :- Endemic colloid goiter :- due to iodine deficiency(less than 50ug/day),no formation of hormones, thyroglobulin accumulates in follicles, increase size of gland Idiopathic non-toxic goiter :- due to unknown cause, gland enlarges without iodine deficiency, suggested due to thyroiditis and deficiency of enzymes (peroxidases, deiodinase…etc.)required for hormone synthesis. some foodstuffs (turnips,cabbage..etc.) contain goitrogenic substances which suppress hormone synthesis.
- 20. TREATMENT OF THYROIDDISORDERS TREATMENT FOR HYPERTHYROIDISM :- I. BY USING ANTITHYROID SUBSTANCES : Drugs which suppresses hormone secretion e.g. Thiocyanate ,thiourylenes ,high cons of inorganic iodides. II. BY SURGRICAL REMOVAL : when antithyroid substances are not possible ,this process is called thyroidectomy. TREATMENT FOR HYPOTHYROIDISM :- Only treatment is administration of thyroid extract or ingestion of pure thyroxine in form of tablets ,orally.
- 21. THYROID DIAGNOSTIC TESTS Functionalstatus of thyroid gland can be assessed by following tests :- i. Measurement of plasma level of T3 and T4 : measure concentration of “free” thyroid hormone in plasma. ii. Measurement of TRH and TSH : these hormones will be total absent in hyperthyroidism dur to –ive feedback by increased level of thyroid hormone iii. Measurement of basal metabolic rate : In hyperthyroidism rate increased by 30% to 60%. In hypothyroidism rate decrease by 20% to 40% .