Parathormone regulates
A) Blood Calcium Level
B) Blood Calcium and Phosphate level
C) Body temperature
D) None of the above

Answer Verified Verified
Hint: The parathyroid hormone is directly present in the bones, kidneys and small intestines.

Complete Answer:
- Parathyroid hormone (PTH), also known as parathormone or parathyrin, is a parathyroid gland-secreted hormone that controls serum calcium concentration through its effects on the bone, kidney, and intestine.
- PTH affects bone remodelling, a mechanism in which bone tissue is alternately resorbed and replaced over time.
- PTH is secreted in response to low Calcium ($Ca^{2+}$) blood serum levels.
- PTH indirectly activates the development of osteoclast in the bone matrix (osteon) to release more ionic calcium ($Ca^{2+}$) into the blood to raise low calcium serum levels.

The bones serve as a (metaphorical) "calcium bench" from which the body can make "removals" as needed to maintain the amount of calcium in the blood at sufficient levels considering the ever-present metabolism, stress, and nutritional variations challenges.

- PTH is "a key to opening the vault on the bank" to extract calcium.
- PTH is mainly secreted by the chief parathyroid gland cells. It is a polypeptide that contains 84 amino acids and is a prohormone. It has a molecular mass approximately 9500 Da.
- The chief cells of the parathyroid glands secrete the parathyroid hormone (PTH), parathormone or parathyrin. It helps to increase calcium concentration ($Ca^{2+}$) in their hair.
- Parathormone also prevents the reabsorption of phosphate by the tubules of the kidney, thereby lowering concentrations of serum phosphates. This potentiates parathormone user's ability to increase serum calcium concentrations because, when serum phosphate concentrations are low, less insoluble calcium-phosphate complexes are produced.

So the answer is “Blood Calcium and Phosphate level”.

Note: For any given time the body retains very close control over the circulating calcium in the blood. The balance is preserved by an intricate interplay of calcium ingested from the intestines, the passage of calcium in and out of the bones, and the reclamation and excretion of calcium in the urine by the kidneys.
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