Thyroid gland  One of largest pure endocrine glands in the body ( 20gms).  Its size depends on: 1. age … age   size. 2. sex … female > male. 3. physiological condition … (pregnancy, lactation)  Site: Located in the neck just below the larynx, on either side of & anterior to the trachea.

Thyroid gland … (Continued)

Thyroid and para

Thyroid gland secretions ● 2 important thyroid hormones: ● Thyroxine (T4) or tetraiodothyronine ● Triiodothyronine (T3) - Secreted by Follicular cells. - Can be stored in thyroid gland for couple of months (2-3 months). - Having significant effect on  metabolic rate of the body. ● Calcitonin - Secreted by Parafollicular cells. - Important hormone for Ca2+ metabolism & homeostasis.

Thyroxine and its precursors: Structure & Synthesis Figure 23-8: Thyroid hormones are made from tyrosine and iodine

Thyroid Hormone:Transport T3 & T4 leave the thyroid gland by diffusion Both are transported in blood by three transport proteins, Thyroxine binding globulin (TBG), transthyretin and albumin A majority (70%) of T4 & T3 is bound to TBG Both enter their target cells by diffusion

Thyroxine and its precursors: Activity T4 mainly functions as a prohormone. T3 is the main active thyroid hormone and has the highest binding affinity for thyroid hormone receptor (TR). Thyroid hormone activity can be increased in plasma without new synthesis by converting T4 to T3. If too much thyroid activity is present T4 is converted to the inactive metabolite rT3 to reduce activity.

T3 & T4 Control Pathways & Diseases from Malfunction Hypothalamus Anterior Pituitary Thyroid Hypothyroidism Goiter (TSH ) Grave's disease

Abnormal thyroid hormones secretions

Overview of Thyroid Disease States Hypothyroidism Hyperthyroidism Overview of Thyroid Disease States. Disorders of the thyroid are common and consist of 2 general presentations: changes in the size or shape of the gland or changes in secretion of hormones from the gland.1 Hypothyroidism refers to the inadequate production of thyroid hormone or diminished stimulation of the thyroid by TSH; hyperthyroidism refers to those conditions in which thyroid hormones are excessively released due to gland hyperfunction. Reference 1. Hardman JG, Limbird LE, eds. Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 9th ed. New York, NY: McGraw Hill; 1996:1383,1394.

Hypothyroidism The most common thyroid disorder Hypothyroidism is a disorder with multiple causes in which the thyroid fails to secrete an adequate amount of thyroid hormone The most common thyroid disorder Usually caused by primary thyroid gland failure Also may result from diminished stimulation of the thyroid gland by TSH Hypothyroidism. Hypothyroidism, known as myxedema when severe, is the most common disorder of thyroid function.1 Most cases of hypothyroidism fall under the category of primary hypothyroidism, in which the thyroid fails to produce sufficient thyroid hormone.1 More infrequently, hypothyroidism is caused by decreased thyroidal stimulation by TSH, which is termed central, hypothyrotropic, or secondary hypothyroidism.2 References 1. Hardman JG, Limbird LE, eds. Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 9th ed. New York, NY: McGraw Hill; 1996:1394. 2. Braverman LE, Utiger RD, eds. The Thyroid: A Fundamental and Clinical Text. 8th ed. Philadelphia, Pa: Lippincott, Williams & Wilkins; 2000:719.

Hypothyroidism

II: Hypothyroidism (myxedema) … cont. Symptoms of Hypothyroidism: - Decreased metabolic rate. - Slow heart rate & pulse. - Slow muscle contractions -  appetite,  weight gain, & constipation. - Prolonged sleep, & dizziness. - Coarse skin. - Slow thinking, lethargy, & mask face. .

90% of hyperthyoidism is due to “Grave’s disease Hyperthyroidism Hyperthyroidism refers to excess synthesis and secretion of thyroid hormones by the thyroid gland, which results in accelerated metabolism in peripheral tissues 90% of hyperthyoidism is due to “Grave’s disease Hyperthyroidism. The term hyperthyroidism is restricted to those conditions in which thyroid hormones are excessively released as a result of gland overactivity.1,2 Iodine uptake by the gland is increased1 and there can be excessive production of body heat, increased motor activity, and increased activity of the sympathetic nervous system.2 References Hardman JG, Limbird LE, eds. Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 9th ed. New York, NY: McGraw Hill; 1996:1393-1394. Braverman LE, Utiger RD, eds. The Thyroid: A Fundamental and Clinical Text. 8th ed. Philadelphia, Pa: Lippincott, Williams & Wilkins; 2000:515-516.

“Grave’s disease

Typical Thyroid Hormone Levels in Thyroid Disease TSH T4 T3 Hypothyroidism High Low Low Hyperthyroidism Low High High Typical Thyroid Hormone Levels in Thyroid Disease. Measurement of the total plasma hormone concentration may not provide an accurate assessment of thyroid gland activity because total hormone concentration is affected by changes in either the amount of thyroxine-binding globulin (TBG) or the affinity of hormones to TBG in plasma.1 For more than 25 years, TSH methods have been able to detect the elevations in TSH that typify hypothyroidism.2 In the past 10 years, the sensitivity of TSH assays has increased to the extent that TSH measurement is now recognized as a more sensitive test than FT4 for detecting both hypo- and hyperthyroidism.2 However, some patients may be incorrectly or incompletely diagnosed if only TSH is measured.3 If serum TSH is high, serum FT4 should be measured to distinguish between mild thyroid failure and overt hypothyroidism.3 If serum TSH is low, both serum FT4 and FT3 should be assayed to identify overt thyrotoxicosis and T3 thyrotoxicosis.3 References 1. Hardman JG, Limbird LE, eds. Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 9th ed. New York, NY: McGraw Hill;1996:1394. 2. Thyroid. 2003;13:33-44. 3. Braverman LE, Utiger RD, eds. The Thyroid: A Fundamental and Clinical Text. 8th ed. Philadelphia, Pa: Lippincott, Williams & Wilkins; 2000:379.

Populations at Risk for Mild Thyroid Failure Women Prior history of Graves disease or postpartum thyroid dysfunction Elderly Other autoimmune disease Family history of Thyroid disease Pernicious anemia Type 1 Diabetes mellitus Populations at Risk for Mild Thyroid Failure. Certain patient populations are at a higher risk for developing mild thyroid failure. Women are at a higher risk than men for developing mild thyroid failure.1 The risk of developing mild thyroid failure increases with age, often reaching a peak of 21% in women and 16% in men over 74 years of age.1 Patients with a family history of thyroid disease, pernicious anemia, and diabetes mellitus also are at risk for developing mild thyroid failure.2,3 References 1. Caraccio N, et al. J Clin Endocrinol Metab. 2002;87:1533-1538. 2. Carmel R, et al. Arch Intern Med. 1982;142:1465-1469. 3. Perros P, et al. Diabetes Med. 1995;12:622-627. Caraccio N, et al. J Clin Endocrinol Metab. 2002;87:1533-1538. Carmel R, et al. Arch Intern Med. 1982;142:1465-1469. Perros P, et al. Diabetes Med. 1995;12:622-627.

function D. Help regulating lipid & CHO metabolism Stimulates formation of proteins, which exert trophic effects on tissues B. Is essential for normal brain development D. Help regulating lipid & CHO metabolism C. Essential for childhood growth E. important for reproductive function F. T3 is an important regulator of skeletal maturation at the growth plate

by Bader al-onazi