THYROID

DR. LAXMIKANTA SAY

“Thyreos” - “A shield”

Largest endocrine gland

Development – floor of pharynx & thyroglossal duct

Wt. 15 – 20 gms

Highly vascular – 5 ml/gm/min

Thyroglobulin - Mol. Wt. 3,35,000

INTRODUCTION

Functions of Thyroid

Maintains Metabolism in tissue - stimulate O2 consumption - regulate lipid & Carbohydrate

metabolism - influence body mass & mentation

Secretion of Calcitonin - regulates Calcium levels

INTRODUCTION CONT….

ANATOMY BLOOD SUPPLY HISTOLOGY

T4

T3

RT3

Calcitonin

HORMONES

IODINE HOMEOSTASIS

Thyroid Cellular Mechanism 1.Iodine trapping 2.Oxidation 3.Synthesis of Thyroglobulin 3.Organification – Iodination of

Tyrosine 4.Release

SYNTHESIS

CHEMISTRY

In Thyroglobulin molecule in colloid

MIT-23% DIT-33% T3-7% T4-35% RT3- Traces

STORAGE

4µg/dl 80µg/dl 2µg/dl

27µg/dl 36µg/dl

31µg/dl 17μg/dl 38µg/dl

SECRETION

THYROID

T4

T3 RT3

T3 & T4 exist in both free & protein bound form

Total plasma T4=8 µgm/dl , T3=0.15 µgm/dl

CARRIAGE

Plasma protein Half

Life

Conc. of PP (mg/dl)

T4 T3

TBG 5 days 2 67% 46%

TT 2 days 15 20% 1%

Albumin

13 days 3500 13% 53%

T4

- 97% of T4 is secreted from thyroid - 99.98 % plasma bound - Plasma conc. 2 ng/dL - Half-Life – 6-7 days - Longer duration of action. - Volume of distribution – 15% of body wt.(10L)

- Prohormone - metabolically inert until deiodinated - 1/3 rd metabolized to T3 & 45% to RT3.

- Liver – Sulphation & Glucoronidation

- Daily loss in stool – 4-5%

METABOLISM

T3

- Normal Plasma level – 0.15 µg/dL - TBG – 99.8% - 0.2% free (0.3ng/dL) - Half-Life – 1-2 days - More potent & more active. - 13% of circulating T3 is by

Thyroid - 87% deiodination of T4.

METABOLISM

Release of T3 & T4

Deiodinase (D1/D2/D3) - a.a selenocycsteine

Factors affecting deiodination - fetal life, - drugs, - selenium, - illness, - fasting,

Plasma t1/2 - T4-6-7days, T3 -1-2days

METABOLISM

Glycoprotein of 211 aminoacids.

MW. – 28,000.

Secretion is pulsatile – midnight secretion

Normal secretion - 110 µgm/ day

Plasma level – 0.2–5.0 µ IUunit/ml

Half Life – 60 min.

TSH

Salivary gland, Gastric mucosa, placenta, Cilliary body, Choroid plexus, Mammary gland

EXTRA THYROID TISSUE OF NIS

THYROID HORMONE ACTIVATION OF TARGET CELLS

METABOLIC ACTION Protein metabolism – Anabolic/ Catabolic

/Myopathy/Osteoporosis Carbohydrate metabolism – Increased Fat metabolism – Decreased Cholesterol BMR – Increased Vitamins – Increased requirement Body Weight – Decreased /Increased CVS – BF,CO,HR,SBP, decreased DBP, RR CNS – Nervousness, anexity, psychoneurotic

tendencies Sleep – Tiredness, difficult to sleep Effect on Endocrine Glands – Secretion of

Insulin, ACTH Sexual Functions – Impotence, Menorrhagia,

Polymeorrhoea.

FACTORS OF REGULATION

TRH SECRETION TSH SECRETION (+) Cold (-) heat, stress,

T3,T4

(+) T3, T4

(-) glucocortiod, dopamine, stress, somatostatin,

T3, T4

REGULATION

1. TSH i. Increased proteolysis of Thyroglobulin ii. Increased activity of the Iodide pump iii. Increased Iodination of Tyrosine iv. Increased size & Increased secretory

activity v. Increased no. Of thyroid cells & change of

epithellium from cuboidal to columnar.

2. cAMP mediated stimulatory effect.3. TRH mediated - Activation of phospholipase

REGULATION

APPLIED ASPECTS

Goiter Hyperthyroidis

m Hypothyroidis

m

GOITER

GOITROGENS

Iodine deficiency Iodine excess Monovalent anions Coupling blocker Inhibitors of iodide conversion Vegetables – Progoitrin,

Progoitrin Activator, Goitrin active antithyroid agent

HYPERTHYROIDISM

CAUSESTHYROID OVER ACTIVITY1. Grave's disease (60 -80% )2.Thyroid Multi Nodular Goiter3.Solitary toxic adenoma4.Hashimoto's thyroiditis5.TSH secreting pituitary adenoma6.Mutation causing activation of TSH

receptor

EUTHYROID / EXTRATHYROIDAL1.Iatrogenic2.Ectopic thyroid tissue

CLINICAL FEATURE

SYMPTOMS SIGNS

Heat intolerance, fatigability, exertional dyspnea, symptom of vit

deficiency, excitability, irritability, nervousness, diarrhea, hyperphagia, thick skin,

Thyrotoxic myopathy , weight loss, warm moist skin, tachycardia, high output cardiac

failure, fine tremor, exophthalmos, lid retraction, thyroid dermatopathy, thyroid acropathy

NB- Thyroid storms

HYPOTHYROIDISM

HYPOTHYROIDISM

CRETINISMMYXEDEMA

CRETINISM

CAUSES - maternal I2 deficiency, - fetal thyroid dysgenesis, - Inborn errors of TH synthesis, - maternal antithyroid Ab that cross

placenta, - fetal hypopituitary hypothyroidism

C/F - mental retardation, dwarfism, potbelly, enlarged and protruded tongue, failure of sexual development, cardiac malformation

T/t- levothyroxin

CRETINISM

MYXEDEMA

CAUSES-Iodine deficiency

Autoimmune

Iatrogenic Infiltrative disease Pituitary failure Hypothalamic

SYMPTOM SIGN

Tiredness, weakness, dry skin, feeling cold, hair loss, poor memory, constipation, wt gain, poor appetite, menorrhegia, husky voice

Myxedema, puffy face, cool peripheral extremity, bradycardia, carpal tunnel syndrome,

Delayed tendon reflex

T/t -levothyroxin

SCREENING OF THYROID DISORDER

THYROID FUNCTION TEST

Tests based on primary function of thyroid1-radioiodine uptake study2-PBI131 in serum3.Butanol Extractable Iodine4.Radioactive Iodine Uptake3-T3 suppression test4-TSH stimulation test5-TRH stimulation test

Tests measuring blood level of TH1-Serum PBI2-Circulating T4 & T3 level3-Circulating TSH level4-Invitro resin uptake of T35.plasma tyrosine level Contd

Tests based on metabolic function of TH

1-BMR2-Serum cholesterol level3-Serum creatinine level 4-Blood sugar level

Scanning of thyroid gland Immunological test

ANTITHYROID DRUGS

1. Drugs inhibit trapping of iodide (I-) - Monovalent anions & metabolic

poisons.2. Thyourylenes - Thyouracil, Carbimazole,

Methimazole)4. Iodine or Iodide

5. β-adrenergic blocking drugs - Propranolol, Atenolol.

THANK YOU

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