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Thyroid-Stimulating Hormone (TSH)

Thyroid-Stimulating Hormone (TSH)

Author: Aaron Mullally

- know which gland secretes TSH

- know what the target tissue of TSH are

- know what cells synthesize and secrete TSH

- know the effects of TSH

- know how TSH secretion is regulated

This packet goes over the basics of thyroid-stimulating hormone (TSH). This hormone will be mentioned again when I discuss the thyroid gland.

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Overview of TSH

TSH is a rather simple hormone to understand since it only has one majore function, regulating the thyroid gland. TSH stimulates growth of the thyroid gland and also increases the amount of thyroid hormones secreted into the blood.

The major stimulus for TSH secretion is a drop in blood thyroid hormone levels. The drop in thyroid hormone levels stimulates the hypothalamus to secrete thyroid-releasing hormone (TRH) into the portal system (hypothalamohypophyseal portal system). Once TRH reaches the anterior pituitary it stimulates the thyrotropes to secrete TSH into the blood stream. TSH will then be circulated to the thyroid gland, which is where its receptors are located. TSH will stimulate the thyroid gland to manufacture more thyroid hormones and cause an increased pumping of iodine into the thyroid cells (follicles). Once our thyroid hormone levels get back to normal this will stimulate the hypothalamus to slow down the release of TRH.

If a person has a severe dietary deficiency in iodine they will be unable to manufacture thyroid hormones. If this happens there will be no "off" switch for the hypothalamus and it will oversecrete TRH to the pituitary, causing TSH levels to be very high. If TSH rises too high this will cause the thyroid gland to enlarge and create what's called a goiter. So how do you think this problem is corrected?

Source: Mind of Aaron

Thyroid-Stimulating Hormone

Source: Self made

TSH Images

Source: Self made