Thyroid and Parathyroid Function
Start with the big picture
Thyroid follicular cells use tyrosine and iodine to synthesize T₃ and T₄, with thyroid peroxidase supporting key synthesis steps. T₄ is the main circulating form, while the more potent T₃ is largely produced in peripheral tissues. Secretion is regulated by the TRH–TSH–thyroid hormone axis, with negative feedback at hypothalamic and pituitary levels. Thyroid hormones affect basal metabolic rate, heart rate, alertness, growth, and brain development. The lesson also introduces parathyroid gland function: PTH raises serum calcium and lowers serum phosphate through effects on bone and renal handling, and by promoting vitamin D activation and intestinal calcium absorption.
What you'll learn
- Describe the thyroid follicle and identify the roles of its cells and colloid.
- Outline the steps and key enzyme involved in thyroid hormone synthesis.
- Compare the circulation, potency, and regulation of T₃ and T₄.
- Summarize major physiological actions of thyroid hormones.
- Explain how PTH affects bone, kidneys, vitamin D activation, calcium, and phosphate.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
