Summary
Thyroxine and triiodothyronine regulate metabolic rate, growth and development.
In depth
Follicular cells make thyroglobulin and iodinate tyrosine; T4 is converted to the more active T3. Calcitonin is made by C cells. Hyperthyroidism (Graves') causes weight loss, anxiety, heat intolerance; hypothyroidism causes fatigue and weight gain.
Thyroid hormones need iodine. They influence nearly all cells. Hypothyroidism is treated with levothyroxine.
Example: congenital hypothyroidism is screened for in newborns.
The thyroid gland in the neck makes thyroxine (T4) and triiodothyronine (T3, the active form) from tyrosine and iodine, stored in colloid as thyroglobulin. Release is controlled by TSH. Nearly every cell has receptors, and the hormones enter cells and act on gene transcription.
They raise basal metabolic rate and oxygen consumption, promote heat production, and are vital for bone growth and brain development in the fetus and infants. Too little (hypothyroidism) causes tiredness, weight gain and cold intolerance, and in babies cretinism; too much (hyperthyroidism, Graves disease) causes weight loss, heat intolerance and rapid heartbeat. Iodine deficiency causes goitre.
Example: iodised salt prevents deficiency.
Calcitonin from the same gland lowers blood calcium.
Frequently asked questions
What is Thyroid Hormones?
Thyroxine and triiodothyronine regulate metabolic rate, growth and development.
Which area of biology covers Thyroid Hormones, and how advanced is it?
Thyroid Hormones is one of the 54 topics in Reproduction & Endocrinology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Endocrine Glands, Hormones, Negative Feedback in Endocrine Control.
Can you give an example of Thyroid Hormones?
Iodised salt prevents deficiency.
What should I learn before Thyroid Hormones?
Work through the Beginner topics in Reproduction & Endocrinology first, such as Reproduction, Asexual Reproduction, Sexual Reproduction, then return to Thyroid Hormones. Intermediate topics assume the Beginner vocabulary.
What topics are related to Thyroid Hormones?
The closest topics to Thyroid Hormones are Endocrine Glands, Hormones, Negative Feedback in Endocrine Control, Pregnancy Hormones. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Thyroid Hormones?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Thyroid Hormones. To practise the whole of Reproduction & Endocrinology, use the Reproduction & Endocrinology quiz.
How is Thyroid Hormones different from Endocrine Glands?
Thyroid Hormones: Thyroxine and triiodothyronine regulate metabolic rate, growth and development. Endocrine Glands: Pituitary, thyroid, adrenals, pancreas and gonads secrete hormones directly into the blood. Read both side by side and note what each one explains.
How should I study Thyroid Hormones step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Endocrine Glands and explain the difference aloud. Finally, take the Reproduction & Endocrinology quiz and come back to this page for any question you miss.