Parathyroid hormone (PTH), parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands as a polypeptide containing 84 amino acids. It acts to increase the concentration of calcium (Ca2+) in the blood, whereas calcitonin (a hormone produced by the parafollicular cells (C cells) of the thyroid gland) acts to decrease calcium concentration. PTH acts to increase the concentration of calcium in the blood by acting upon the parathyroid hormone 1 receptor (high levels in bone and kidney) and the parathyroid hormone 2 receptor (high levels in the central nervous system, pancreas, testis, and placenta).PTH half-life is approximately 4 minutes. It has a molecular mass of 9.4 kDa.

1. Parathyroid hormone (PTH), is secreted by the chief cells of the parathyroid glands as a
polypeptide containing 84 amino acids.
It acts to increase the concentration of calcium (Ca2+) in the blood.
Calcitonin (a hormone produced by the parafollicular cells (C cells) of the thyroid gland) acts to
decrease calcium concentration.
PTH acts to increase the concentration of calcium in the blood by
acting upon the parathyroid hormone 1 receptor (high levels in
bone and kidney) and the parathyroid hormone 2 receptor (high
levels in the central nervous system, pancreas, testis, and
placenta).
Parathyroid Hormone (PTH)

2. PTH
action in
Calcium
regulation

3. Parathyroid hormone-related
protein (or PTHrP) is a protein
member of the parathyroid hormone
family.
It is occasionally secreted by
cancer cells (breast cancer, certain
types of lung cancer including
squamous cell carcinoma).
1,25(OH)2D:
1,25-dihydroxyvitamin D3, is the
hormonally active form of vitamin D with three
hydroxyl groups.
It increases the level of calcium (Ca2+) in the
blood by (1) increasing the uptake of calcium
from the gut into the blood, and (2) possibly
increasing the release of calcium into the blood
from bone.
PTHrP:
PTHrP acts as an endocrine, autocrine,
paracrine hormone.
Calcitonin and PTH action PTH mode of action