Ure 1318


The hormones thyroxine and triiodothyronine have very similar molecular structures.

The thyroid gland produces calcitonin, but it is usually not referred to as a thyroid hormone because it is synthesized by the C cells, which are distinct from the gland's follicles. Calcitonin plays a role in the control of blood calcium and phosphate ion concentrations. It helps lower concentrations of calcium and phosphate ions by decreasing the rate at which they leave the bones and enter extracellular fluids by inhibiting osteoclasts (see chapter 7, p. 202). At the same time, calcitonin increases the rate at which calcium and


Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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