Glossary of Physiology Terms
There are
7 glossary search results for:
TSH
Definition:
Goiter is an enlargement of the thyroid gland caused most commonly by iodine deficiency in the diet. Iodine deficiency leads to low levels of thyroid hormone production, and a reduction in thyroid hormone negative feedback on the hypothalamus and the anterior pituitary leads to a compensatory rise in the thyroid stimulating hormone (TSH). Enlargement of the thyroid gland is, therefore, caused by abnormally high circulating levels of TSH, which has a strong trophic effect on the thyroid gland.
Definition:
Hyperthyroidism refers to a pathophysiological condition in which the thyroid gland produces and releases abnormally high levels of the thyroid hormones (T
3 and T
4).
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.
Related glossary terms/phrases:
HypothyroidismEuthyroidism
Definition:
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 (T
3 and T
4).
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.
Related glossary terms/phrases:
Primary hypothyroidismSecondary hypothyroidismTertiary hypothyroidismHyperthyroidismEuthyroidism
Definition:
Primary hypothyroidism is characterized by abnormally low levels of thyroid hormone (T
3 and T
4) production, where the defect is at the level of the thyroid gland itself.
In primary hypothyroidism, the circulating levels of the thyroid hormones are low, however, the levels of the thyroid stimulating hormone (TSH) are high due a lack of thyroid hormone negative feedback on the anterior pituitary.
Common causes of primary hypothyroidism include iodine deficiency (which leads to
goiter), and
Hashimoto's disease, in which autoimmune antibodies destroy the ability of the thyroid gland to produce the thyroid hormones.
Related glossary terms/phrases:
HypothyroidismSecondary hypothyroidismTertiary hypothyroidism
Definition:
Secondary hypothyroidism is characterized by abnormally low levels of thyroid hormone (T
3 and T
4) production, where the defect is at the level of the anterior pituitary gland.
In secondary hypothyroidism, the anterior pituitary gland is unable to produce sufficient levels of the thyroid stimulating hormone (TSH) which, in turn, leads to insufficient stimulation of the thyroid gland to produce the thyroid hormones (T
3 and T
4).
Thus, in secondary hypothyroidism, the circulating levels of both TSH and the thyroid hormones (T
3, and T
4) are abnormally low
Related glossary terms/phrases:
HypothyroidismPrimary hypothyroidismTertiary hypothyroidism
Definition:
Tertiary hypothyroidism is characterized by abnormally low levels of thyroid hormone (T
3 and T
4) production, where the defect is at the level of the hypothalamus.
In tertiary hypothyroidism, the hypothalamus is unable to produce sufficient levels of thyrotropin release hormone (TRH). Low TRH levels lead to low production of the thyroid stimulating hormone (TSH) by the anterior pituitary gland which, in turn, leads to insufficient stimulation of the thyroid gland to produce the thyroid hormones (T
3 and T
4).
Thus, in tertiary hypothyroidism, the circulating levels of TRH, TSH, T
3, and T
4 are all abnormally low.
Related glossary terms/phrases:
HypothyroidismPrimary hypothyroidismSecondary hypothyroidism
Definition:
Endocrine cell of the anterior pituitary gland responsible for synthesizing and releasing thyroid stimulating hormone (TSH).
Posted: Sunday, March 31, 2013
Last updated: Friday, August 28, 2015