Calcium Homeostasis and Parathyroid Hormone - PTH

Calcium Homeostasis and Parathyroid Hormone (PTH)

Blood calcium is normally maintained at about 8–10 mg/dL. This range is important not only for bone health but also for nerve signaling, neurotransmitter release, and muscle and heart contraction.

When blood calcium falls, calcium-sensing receptors in the parathyroid glands detect the change and prompt the glands to release more parathyroid hormone (PTH).

How PTH Raises Blood Calcium

• Bones: PTH reduces osteoblast activity and increases osteoclast activity, promoting the release of calcium from bone into the blood.
• Kidneys: PTH increases calcium reabsorption, so more calcium returns to the bloodstream and less is lost in urine.
• Intestines: PTH supports calcium absorption indirectly by promoting the production of calcitriol, the active hormonal form of vitamin D. Calcitriol signals intestinal cells to absorb calcium from food.

Overall Sequence

Low blood calcium → increased PTH → calcium released from bone, retained by the kidneys, and absorbed from food with calcitriol’s help → blood calcium rises toward its normal range.

Speakers and Source

• Speaker: One unnamed narrator
• Source: Calcium Homeostasis and Parathyroid Hormone – PTH, from the Physiology & Anatomy Videos channel