16.8 Parathyroid Gland; Endocrine system

Four to eight tiny yellow-brown glands embedded in

posterior aspect of thyroid

Contain oxyphil cells (function not clear) and parathyroid cells that secrete

parathyroid hormone (PTH), or parathormone

PTH is most important hormone in Ca²⁺ homeostasis

• Secreted in response to low blood levels of Ca²⁺  

• Inhibited by rising levels of Ca²⁺

• Target organs are skeleton, kidneys, and intestine

Parathyroid Gland Functions to -

• Stimulate osteoclasts to digest bone matrix and release Ca²⁺ to blood 

• Enhances reabsorption of Ca²⁺ and secretion of phosphate (PO₄^3-) by kidneys

• Promotes activation of vitamin D by kidneys, which leads to increased absorption of Ca²⁺ by intestinal mucosa