QS Study

Actions of Parathyroid Hormone

Parathyroid hormone regulates the body’s calcium levels. It controls the calcium in our blood and bones. The thyroid gland regulates the body’s metabolism and has no effect on calcium levels while parathyroid glands control calcium levels and have no consequence on metabolism. It acts directly on the skeleton to promote calcium release from bone and on the kidney to enhance calcium reabsorption.

Fig: Actions of Parathyroid Hormone

Action of the parathyroid hormone 

  1. On GIT: 25-OH-D3 → 1,25 – (OH)2 – D2 →↑ Ca2+ and PO43-
  1. On body fluid: It elevates the extracellular body fluid Ca++ conc. by increasing bone resorption.
  1. On bones: It elevates the ECF Ca++ conc. due to –

(i) Immediate activation of osteoclasts,

(ii) Rapid formation of new osteoclast from mesenchymal stem cells.

(iii) Delaying the conversion of osteoclasts to osteoblast.

(iv) Depressing the osteoblastic activity.

  1. On kidney:

(i) Increase the renal tubular reabsorption of Ca++ (DT)

(ii) Increase the excretion of PO43- through urine.

  1. On mammary gland:

↓ rate of Ca++ secretion by the lactating mammary gland.