The Thyroid (Part 2) – Metabolic effects of Thyroid hormone; Hyperthyroidism

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METABOLIC EFFECTS OF THYROID HORMONES

• The Thyroid hormone has Calorigenic effect  (thermogenesis).
• Thyroxine increases cellular metabolism. BMR is increased.
• It stimulates RNA synthesis with consequent increase in protein synthesis.
• Higher concentration of T3 causes protein catabolism and negative nitrogen balance.
• Gluconeogenesis and carbohydrate oxidation are increased.
• Fatty acid metabolism is increased.
• Cholesterol degradation is increased.

ABNORMALITIES OF THYROID FUNCTION

1. Hyperthyroidism.
2. Hypothyroidism.
3. Goiter – Enlargement of thyroid gland.

GOITER

1. Euthyroid goiter – diffuse enlargement.
2. Nodular goiter which may lead to hyperfunction, or
3. Iodine deficiency goiter which may result in hypothyroidism.

HYPERTHYROIDISM

Hyperthyroidism may be due to:

• Increase in binding protein & Increased affinity of binding protein
• Effects of autoantibodies
• TSH secreting tumors and
• T4 toxicosis (T4 increase; T3 low)

SYMPTOMS OF HYPERTHYROIDISM

1. Increased rate of metabolism
2. Weight loss
3. Tachycardia
4. Fine tremors
5. Sweating
6. Diarrhea
7. Emotional disturbances
8. Anxiety and
9. Sensitivity to heat

CAUSES OF HYPERTHYROIDISM

1. Toxic goiter
2. Graves’ disease
3. Excess intake of thyroid hormones
4. Rarely, TSH secreting tumors of pituitary

PRIMARY HYPERTHYROIDISM

It is due to the diseases of the Thyroid gland. It is seen in:

1. Grave’s disease
2. Toxic multinodular goiter
3. Toxic adenoma
4. Functioning metastatic thyroid carcinoma
5. TSH receptor mutation
6. Struma ovarii (teratomas of ovary),
7. Iodine excess

SECONDARY HYPERTHYROIDISM

It is due to diseases of pituitary or hypothalamus.

Seen in:

1. TSH secreting pituitary adenoma
2. Thyroid hormone resistance syndrome
3. Chorionic gonadotropin secreting tumors &
4. In gestational thyrotoxicosis

LAB FINDINGS IN HYPERTHYROIDISM