Parathormone (Parathyroid hormone/PTH) increase calcium levels and reduces phosphate level by acting on
**Core Concept**
Parathormone (PTH) is a hormone secreted by the parathyroid glands that plays a crucial role in regulating calcium and phosphate levels in the blood. The primary function of PTH is to maintain normal calcium levels by increasing bone resorption, reducing phosphate reabsorption in the kidneys, and enhancing calcium absorption in the intestines.
**Why the Correct Answer is Right**
PTH acts on the kidneys to inhibit phosphate reabsorption in the proximal tubules, leading to increased excretion of phosphate in the urine. This results in a decrease in serum phosphate levels. Additionally, PTH promotes the activation of vitamin D, which in turn increases calcium absorption from the intestines. The increased calcium levels in the blood are achieved through PTH-mediated bone resorption, where osteoclasts are activated to break down bone tissue, releasing calcium ions into the bloodstream.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because PTH does not primarily act on the thyroid gland to regulate calcium levels. While the thyroid gland is involved in regulating metabolism, PTH's primary action is on the kidneys and bones.
**Option B:** This option is incorrect because PTH does not primarily act on the adrenal glands to regulate calcium levels. The adrenal glands are involved in regulating electrolyte balance and stress response, but PTH's primary action is on the kidneys and bones.
**Option C:** This option is incorrect because PTH does not primarily act on the pancreas to regulate calcium levels. The pancreas is involved in regulating blood sugar levels, but PTH's primary action is on the kidneys and bones.
**Option D:** This option is incorrect because while PTH does have some effects on the liver, its primary action is on the kidneys and bones.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that PTH has a dual effect on calcium and phosphate levels. While it increases calcium levels by promoting bone resorption and enhancing calcium absorption, it also reduces phosphate levels by inhibiting phosphate reabsorption in the kidneys.
**Correct Answer:** D. The kidneys