This lesson introduces the thyroid’s structure and explains how it produces and releases its main hormones, triiodothyronine (T₃) and thyroxine (T₄). Understanding this process shows how the body coordinates thyroid hormone levels with its needs.
The thyroid gland is a butterfly-shaped organ located in front of the trachea and just below the larynx. Its narrow middle region is the isthmus, which connects the two wing-shaped lobes. Parathyroid glands are embedded in the thyroid lobes, mostly on their posterior surfaces.
All flashcards
How does TSH affect iodide uptake by thyroid follicle cells?
TSH stimulates the cells to actively transport iodide from the blood, concentrating it inside the cells.
How are T₃ and T₄ assembled from iodinated tyrosine residues?
One-iodine and two-iodine residues combine to form T₃; two two-iodine residues combine to form T₄.
Why is most circulating thyroid hormone bound to transport proteins?
Protein binding limits immediate entry into cells and provides a reserve that can replenish free hormone.
How does the body produce T₃ from T₄?
Many cells remove one iodine atom from T₄, producing the more potent hormone T₃.
What is calcitonin’s effect on osteoclasts?
Calcitonin inhibits osteoclast activity, reducing bone breakdown and the release of calcium into blood.
Quiz questions
What is the calorigenic effect of thyroid hormones?Answer: Increased heat production as energy is released during cellular metabolism.
What causes Graves’ disease to overstimulate thyroid follicle cells?Answer: Antibodies that stimulate the cells.
How can persistent iodine deficiency contribute to goiter formation?Answer: Low thyroid hormone levels increase TSH stimulation, which can enlarge the gland.
What is exophthalmos?Answer: Forward bulging of the eyes associated with inflammation of tissues in the eye sockets.
Which effect can excess thyroid hormone have on the cardiovascular system?Answer: It can increase sensitivity to epinephrine and norepinephrine, contributing to a faster, stronger heartbeat.
Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.