3normal amount of thyroid hormones are essential for normal growth and development by maintaining the level of energy metabolism in the tissue.Either too little or too much thyroid hormones will bring disorders to the body.
4Part 1 Thyroid hormones Two major thyroid hormones are: triiodothyronine（T3, the most active form）thyroxin（T4）The characteristic of their chemical structure is that they all contain iodine as an essential part of the molecule.
6inadequate secretion of thyroid hormone (hypothyroidism) can bring many disorders to the body (eg. bradycardia, poor resistance to cold, both mental and physical slowing.)
7[Synthesis, storage and release of thyroid hormones]
8SynthesisIodine is the raw material of the thyroid biosynthesis. Once taken up by the thyroid gland, iodine undergoes a series of enzymatic reactions before it converts into active thyroid hormones.
9Synthesis; four steps1. iodine trapping :uptake of iodine by the thyroid gland2. oxidation of iodine: (to its active form)thyroid peroxidase (key enzyme of the synthesis)3. iodide organification :the iodination of tyrosyl groups of thyroglobulinproductions: MIT and DIT4. formation of T4 and T3 from MIT and DIT :thyroid peroxidase
10storagestore in the colloid droplets of thyroglobulin
11release The hormones are released by proteolysis of thyroglobulin . Enzyme: thyroglobulin hydrolaseThe ratio of T4 to T3 within thyroglobulin is about 5:1
12Differences between T3 and T4 the effect of T3 is much faster, stronger and shorter than that of T4.
13conversionT4 can converse to T3 through deniodonite in peripheral tissues as well as in the thyroid.(catalyzed by deiodinase)
14Regulation: TRH Hypothalamus pituitary TSH T3,T4 thyroid Controled by HPT(hypothalamic-pituitary-thyroid) axis
18Pharmacological actions Effects on growth and developmentCalorigenic effects :Hypersensitivity to catecholamine :
19Pharmacological actions 1.Effects on growth and development :responsible for normal growth and maturation of human being , especially for nervous and skeletal tissues.so the absence of thyroid hormones before birth leads to both mental and physical retardation（cretinism）
20Pharmacological actions 2.Calorigenic effects:T3 /T4 can increase oxygen consumption, promote metabolism and BMR（basal metabolic rate） ,↓utility.So hyperthyroidism will result in excess heat production and body wasting.
24Clinical usesthe major indications for the therapeutic use of thyroid hormones are for hormone replacement therapy in patients with hypothyroidism .
25Clinical uses 1.Cretinism :congenital hypothyroidism often happens in newborn babies, mainly caused by iodine deficiency before birth .Success in the treatment of cretinism depends on the age at which therapy is started.The earlier, the better.
26Cretinism Symptoms: 1.Physical slow: dwarf, with short extremities , 2.mentally retarded: inactive, uncomplaining and listless.incidence :about 1 per 400 birthsPrevention and therapy:Prevention: Iodine replacement is the best method prior to pregnancy.Therapy: thyroid hormones replacement(T4 is more often used than T3)
27Clinical uses 2.Myxedema: adult hypothyroidism Happens after individual developmentSlow in mentalityWith special edemaMortality :60%
28Clinical uses 3.Simple goiter: A kind of prevalent disease caused by insufficient dietary iodineTSH can promote hyperplasy and hypertrophy of thyroid gland.4. Differential diagnosis of simple goiter and hyperthyroidism
34Treatment of hyperthyroidism The goal of therapy is to decrease the additional hormone and attend to normal levels.Can be accomplished byremoving part of the glandInhibiting synthesisBlocking releasing
35four categories of anti-thyroid drugs Ⅰ Thioureas : (硫脲类)interfere directly with the synthesis of thyroid hormonesⅡ High concentrations of iodine :decrease the release of thyroid hormonesⅢ Radioactive iodine :damage the gland with ionizing radiationⅣ β- receptor antagonists:control the manifestations
38Ⅰ Thioureas Pharmacological action : Mechanism Decrease the level of thyroid hormonesMechanism1.inhibit the thyroid peroxidase :(key enzyme of synthesis)interfere the oxidation of iodine and the coupling of MIT and DIT to form T3/T4
392. inhibit conversion from T4 to T3 3.immunosupressive effect: TSI
40Pharmacokinetics:AbsorptionDistributionExcretionPass through placenta, milk
41Therapeutic uses 1.As definitive treatment to control hyperthyroidism 2.Preoperative preparations for subtotal thyroidectomy: to control the disorder in preparation for surgical treatment.(thioureas plus large dose of iodine)3. Thyroid crisis Propylthiouracil is the first choice.
44Ⅱ Iodine and iodide Oldest agent have completely different effects due to different doses
45Pharmacological effects in small dose:↑ synthesis of thyroid hormonesin large dose : antithyroid1) ↓the release of thyroid hormones into the circulation: strongMechanism: Inhibit thyroglobulin hydrolase2)↓synthesis of thyroid hormones: weakMechanism: Inhibit thyroid peroxidase
46Therapeutic uses 1.Simple goiter : in small dose 2.In preparation for thyroidectomy :used after the hyperthyroidism has been controlled by thioureas, given for 7 to 10 days immediately preceding the operation. (The changes after a fairly long term of administration include: the vascularity of the thyroid gland is reduced, the gland becomes much firmer and smaller.)3.Thryotoxic crisis
48Ⅲ Radioactive iodine 131I : most often used isotope of iodine γ rays（1%）:β particles（99%): destructive
49Effects on the thyroid gland 131I is rapidly and efficiently trapped by the thyroid gland and slowly emitsβparticles and γrays.The destructive βparticles can destroy the thyroid cells with little damage to surrounding tissues (the penetration range is only mm).Theγrays can pass through the tissue and be quantified by external detection
50Clinical uses1.hyperthyroidism: administrated orally and the effective dose differs for individual patients.2.diagnosis of thyroid functions
51pregnancy and milk mothers Adverse reactions:hypothyroidismcontraindicationspregnancy and milk mothers
52IV β-adrenergic receptor antagonists adjuvant therapymany of the symptoms of hyperthyroidism are associated with sympathetic stimulation, so β-R blockers are effective in antagonizing the catecholaminegic symptoms such as tachycardia, palpitations ,anxiety and tension.
53Action: (1)block 1-R of heart (2)block -R of CNS (3) block -R of presynaptic membrane of peripheral nerve.(4) Inhibit T4 converted into T3
54Uses:1.Control the symptoms ofhyperthyroidism beforeconfirmed diagnosis2.Thyroid crisis3.Preoperation of hyperthyroidism4.Hyperthyroidism