12/26/2008

CONGENITAL HYPOTHYROIDISM Marc E. Tischler, PhD; University of Arizona

CONGENITAL HYPOTHYROIDISM

•thyroid hormones (T4,T3) are made by the follicular cells of the thyroid gland (Figure 1) •production of thyroid hormones is signaled by thyroid stimulating hormone (TSH) from the anterior pituitary (Figures 1,2) • eeeacoeyodgad(gue)oacoS(gue)wpeveither lack of the thyroid gland (Figure 1) or lack of TSH (Figure 2) will prevent production of thyroid hormone leading to the disease •thyroid hormone functions: o growth o maintaining body’s basal metabolic rate (BMR) o heat production o promoting sweating • consequences of hypothyroidism (low blood thyroid concentration) o low BMR weight gain o sluggishness, decreased heart rate o intolerance to cold o dry skin

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COLLOID SPACE THYROID FOLLICULAR CELL IT IT IT T3 IT T T IT Tgb IT 3 4 DISEASE + IT Tgb I Tgb IT T4 IT T4 (no TSH or no - Iodination T I Hormone 4 thyroid cells) Formation T T

T T T3 T3 T4 Thyroglobulin (Tgb) Tgb T4 Thyroglobulin (Tgb) T4 T NORMAL 4 X TSH Hormone stimulates I- release cell I- X Thyroid stimulating I- BLOOD hormone (TSH) Thyroid Figure 1. Iodine from the blood is attached to tyrosine (T) on thyroglobulin (Tgb) in the colloid. hormones Thyroid hormones form on the iodinated Tgb, then are released from Tgb in the cell, and finally move to the blood. All events including iodine uptake into the cell and cell growth are triggered by thyroid T4, T3 stimulating hormone (TSH) (see also Fig. 2). In congenital hypothyroidism either the thyroid cells are absent or TSH is lacking (right) (X). Patients require hormone replacement therapy.

NORMAL DISEASE Hypothalamus Hypothalamus X Inhibitory signals by Loss of thyroid Thyrotropin releasing hormone (TRH) inhibitory hormone signals

Anterior pituitary gland Anterior pituitary gland X

Thyroid stimulating hormone (TSH) X

either no TSH or no cells Thyroid hormones Thyroid gland: hormone secretion T4, T3 and cell growth X

Figure 2. TRH from hypothalamus region of the brain signals anterior pituitary to release TSH. TSH signals thyroid gland to make and release thyroid hormones and promote cell growth. In congenital hypothyroidism either lack of TSH or lack of cells (X) means no thyroid hormone in the blood leading to the symptoms listed in the second slide.

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