Hyperthyroidism refers to a pathophysiological condition in which the thyroid gland produces and releases abnormally high levels of the thyroid hormones (T₃ and T₄).

The symptoms of hyperthyroidism may include high metabolic rate, weight loss, nervousness, excess heat production, tachycardia, and tremor.

Two main forms of hyperthyroidism exist: (1) Primary hyperthyroidism, and (2) Secondary hyperthyroidism.

In primary hyperthyroidism, the thyroid gland produces high levels of the thyroid hormones, either as a result of a secretory tumor of the thyroid gland, or under the control of thyroid stimulating immunoglobulins (such as in Graves' disease).

Secondary hypothyroidism is caused by high levels of thyroid stimulating hormone (TSH) produced by the anterior pituitary gland. TSH then stimulates the thyroid gland to produce excessive amounts of the thyroid hormones.

Hypothyroidism
Euthyroidism

Hypothyroidism refers to a pathophysiological condition in which the thyroid gland does not produce sufficient amounts of the thyroid hormones (underactive thyroid), leading to abnormally low levels of the thyroid hormones (T₃ and T₄).

The symptoms of hypothyroidism may include reduced metabolic rate, chronic fatigue, weight gain, myxedema, and depression.

Three main forms of hypothyroidism exist: (1) Primary hypothyroidism, (2) Secondary hypothyroidism, and (3) Tertiary hypothyroidism.

In primary hypothyroidism, the thyroid gland itself is incapable of producing normal levels of the thyroid hormones.

Secondary hypothyroidism is caused by low levels of thyroid stimulating hormone (TSH). TSH, produced by the anterior pituitary gland, is required to stimulate the thyroid gland to produce the thyroid hormones.

Tertiary hypothyroidism is caused by low levels of thyrotropin releasing hormone (TRH). TRH, produced by the hypothalamus, is required to stimulate the anterior pituitary gland to produce TSH which, in turn, is required to stimulate the thyroid gland to produce the thyroid hormones.

Primary hypothyroidism
Secondary hypothyroidism
Tertiary hypothyroidism

Hyperthyroidism
Euthyroidism

Synaptic pathology. Any pathophysiological condition that leads to abnormal function of synapses within the nervous system. The pathology may be due to pre-synaptic and/or post-synaptic mechanisms, or may involve glial cells surrounding synapses.