Hypoparathyroidism is decreased function of the parathyroid glands with underproduction of parathyroid hormone. This can lead to low levels of calcium in the blood, often causing cramping and twitching of muscles or tetany (involuntary muscle contraction).

Tetany is an abnormal condition characterized by periodic painful muscular spasms and tremors, caused by faulty calcium metabolism and associated with diminished function of the parathyroid glands.

Vitamin D increases blood concentrations of calcium. It is generated through the activity of parathyroid hormone within the kidney. The most important effect of vitamin D is to facilitate absorption of calcium from the small intestine. Along with thyroid hormone, vitamin D also enhances fluxes of calcium out of bone.

Parathyroid hormone (PTH), parathormone or parathyrin, is secreted by the chief cells of the parathyroid glands. It acts to increase the concentration of calcium ($Ca^{2+}$) in the blood. Parathormone also inhibits the reabsorption of phosphate by the kidney tubules, thereby decreasing serum phosphate concentrations. This potentiates the ability of parathormone to increase serum calcium concentrations because fewer insoluble calcium-phosphate complexes are formed when serum phosphate concentrations are low.

Parathormone of parathyroid gland reduces the blood phosphate level while increases the blood calcium level. Antagonistic functions of insulin and glucagon hormones of pancreas maintain the homeostasis of blood glucose level. Thyroid hormones regulate the metabolic rate of the body. Thymus hormone serves in the differentiation of lymphocytes present inside the lobules. Thus, the correct answer is D.

A low level of parathyroid hormone (hypoparathyroidism) can cause hypocalcemia, which results when too much calcium is lost in urine or when not enough calcium is moved from bones into the blood. 

Parathyroid hormone is secreted by the parathyroid glands and is the most important regulator of calcium levels in the blood and within the bones. Parathyroid hormone is mainly controlled by the negative feedback of calcium levels in the blood to the parathyroid glands. Low calcium levels in the blood stimulate parathyroid hormone secretion, whereas high calcium levels in the blood prevent the release of parathyroid hormone.

Hypoparathyroidism is the state of decreased secretion or activity of parathyroid hormone (PTH). This leads to decreased blood levels of calcium (hypocalcemia) and increased levels of blood phosphorus (hyperphosphatemia).

Parathyroid hormone (PTH) or parathormone 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 in the blood.

Parathyroid hormone is mainly controlled by the negative feedback of calcium levels in the blood to the parathyroid glands. Low calcium levels in the blood stimulate the parathyroid hormone secretion, whereas high calcium levels in the blood prevent the release of parathyroid hormone. 

The parathyroid glands are four tiny glands, located in the neck, each gland is about the size of a grain of rice. Parathyroid gland secretes parathormone hormone, which regulates $Ca^{++}$ and phosphate ion in the body. This gland works independently to the pituitary gland. 

Parathormone of parathyroid gland increases the blood calcium level by binding to receptors present on DCT of the nephron to stimulate conditional reabsorption of calcium. Thyroid hormone does not have any specific target cell and stimulate metabolic rate by all cells. Glucagon regulates blood glucose level while growth hormone stimulate overall growth and development. Calcitonin hormone stimulates a temporary reduction in number and activity of osteoclasts (bone cells) and thereby reducing the blood calcium level. Thus, the correct answer is option A.

• Parathyroid hormone regulates calcium levels in the blood, largely by increasing the levels when they are too low. 
• It does this through its actions on the kidneys, bones and intestine. 
• Bone parathyroid hormone stimulates the release of calcium from large calcium stores in the bones into the bloodstream. Hence, Parathyroid maintains the calcium level in the blood by action on Bone, Kidney and Intestine.
So, the correct answer is 'All of the above'.

Thymus is well developed in new born child and grows upto the age of puberty after that it starts shrinking and almost disappears in old age.

The parathyroid glands are small endocrine glands in the neck that produce parathyroid hormone. Humans have four parathyroid glands, which are usually located behind the thyroid gland and in rare cases, within the thyroid gland or in the chest. Parathyroid glands control the amount of calcium in the blood and within the bones.

Hormone released by the parathyroid gland is parathyroid hormone also called parathormone or parathyrin, this hormone regulates the Ca$^{+2}$ concentration in the serum by acting upon bone, kidney and intestine.

Parathormone secreted by parathyroid gland regulates the level of calcium in the blood. It stimulates the release of calcium from the bones into the blood, increases calcium absorption from the intestine into the blood and it also increases calcium reabsorption from the nephrons into the blood. Therefore, its deficiency leads to low blood calcium level.

The kidney processes Vitamin D into calcitriol, the active form that is most effective in assisting intestinal absorption. This process is stimulated by parathyroid hormone. Vitamin D is an important co-factor in the intestinal absorption of calcium, as it increases the number of calcium binding proteins, involved in calcium absorption through the apical membrane of enterocytes in the small intestine.

Parathyroid glands are small endocrine glands in the neck of humans and other tetrapods that produce parathyroid hormone. Humans usually have four parathyroid glands, variably located on the back of the thyroid gland. Parathyroid hormone and calcitonin (one of the hormones made by the thyroid gland) have key roles in regulating the amount of calcium in the blood and within the bones. The major function of the parathyroid glands is to maintain the body's calcium and phosphate levels within a very narrow range, so that the nervous and muscular systems can function properly. The parathyroid glands do this by secreting parathyroid hormone.

Thyrocalcitonin (TCT) is secreted when calcium level in blood is high. It then lowers the levels by suppressing  release of calcium ions from bones. Whereas parathyroid hormone increases the blood calcium level by increasing calcium absorption from intestine and mobilising calcium from bones to blood.

Parathyroid gland secretes hormone called parathormone (PTH). This hormone regulates calcium and phosphate balance between blood and other tissue. so, if parathyroid gland degenerates calcium concentration will be adversely affected.

 A parathyroid gland tumor can prompt hypersecretion of PTH. This can raise blood calcium levels so excessively that calcium deposits begin to accumulate throughout the body, including in the kidney tubules. When calcium levels in your blood fall too low, your parathyroid glands secrete enough PTH to restore the balance but sometimes these glands produce an excess amount of hormone, leading to abnormally high levels of calcium (hypercalcemia) and low levels of phosphorus in your blood.

Bovine parathormone is a large polypeptide having 84 amino-acids. It was discovered and purified by Philips Collip in 1925. 

• In humans, four parathyroid glands are present on the back side of the thyroid gland, one pair each in the two lobes of the thyroid gland.
• The parathyroid glands secrete a peptide hormone called parathyroid hormone (PTH) or parathormone.
• Parathormone increases the $Ca^{2+}$ levels in the blood.
  
• Increase in bleeding time and delay in blood coagulation is due to the deficiency of parathormone because its deficiency causes a decrease in blood calcium levels and calcium ion is essential for blood coagulation.
  
• So, the correct answer is 'Parathormone'.

In humans, four parathyroid glands are present on the back side of the thyroid gland, one pair each in the two lobes of the thyroid gland. They secrete a peptide hormone called parathyroid hormone (PTH).
PTH increases Ca2+ absorption from the digested food. it also stimulates reabsorption of Ca2+ by the renal tubules.PTH acts on bones and stimulates the process of bone resorption (dissolution/demineralization). 
 Hence PTH is a hypercalcemic hormone, i.e., it increases the blood Ca2+ levels. Along with TCT(Thyrocalcitonin), it plays a significant role in calcium balance in the body

• Parathyroid hormone- It is also known as parathormone or parathyrin.
• It is a secreted by the parathyroid glands.
• Its main function includes bone remodelling by releasing more PTH when the calcium in our blood goes too low, which increases the blood calcium level that is released from bones.
• This hormone stimulates calcitriol production in the kidney as it synthesises 1-α hydroxylase and also maintains calcium levels by increasing calcium absorption in the gastrointestinal tract 
• Hypoparathyroidism- leads to low levels of calcium in the blood which causes cramps and twitches in muscles or tetany.
• So, the correct answer is 'More PTH is released when blood calcium level rises'.

• In addition, tetraiodothyronine or thyroxine (T4) and triiodothyronine (T3) Thyroid gland also secretes a protein hormone called thyrocalcitonin. 
• Thyrocalcitonin(TCT) lowers blood calcium levels. It counters the actions of parathyroid hormone which increases the blood calcium level.
• The parathyroid glands monitor the calcium in the blood 24 hours per day. The four parathyroid glands make more or less parathyroid hormone (PTH) in response to the level of calcium in the blood. When the calcium in our blood goes too low, the parathyroid glands make more PTH in order to increase the blood calcium levels.
  
• Hence Thyrocalcitonin and Parathyroid hormones coordinate with each other to maintain ideal blood Ca level.
• So, the correct answer is 'Thyrocalcitonin and Parathyroid hormone'.

The parathyroid glands secrete a peptide hormone called parathyroid hormone or parathormone (PTH). The release of parathromone is regulated by the circulating levels of calcium ($Ca^{2+}$) ions in the blood. PTH plays an important role in calcium balance of the body. It maintains the calcium balance between the blood and other tissues. When the calcium level in the blood decreases, parathyroid hormone is released in order to increase the calcium level in the blood. PTH acts on bones and other skeletal structure and mobilizes the calcium ($Ca^{2+}$) from the bones into the blood. This is called bone resorption/dissolution/demineralization. The parathromone also increases the reabsorption of calcium by the renal tubules and absorption of calcium from the digested food. Hence, PTH (parathormone) is a hypercalcemic hormone that increases the blood calcium levels.

The thyroid gland secretes a protein hormone called thyrocalcitonin (TCT) which regulates the blood calcium levels. Parathyroid hormone (PTH) increases the calcium levels in the blood. It also stimulates reabsorption of calcium by the renal tubules and increases calcium absorption from the digested food.

Parathormone is a hypercalcemic hormone that increases the blood calcium levels. The parathyroid glands secrete a peptide hormone called parathyroid hormone or parathormone (PTH). The release of parathromone is regulated by the circulating levels of calcium ($Ca^{2+}$) ions in the blood. PTH plays an important role in calcium balance of the body. It maintains the calcium balance between the blood and other tissues. When the calcium level in the blood decreases, parathyroid hormone is released in order to increase the calcium level in the blood. PTH acts on bones and other skeletal structure and mobilizes the calcium ($Ca^{2+}$) from the bones into the blood. This is called bone resorption/dissolution/demineralization. The parathromone also increases the reabsorption of calcium by the renal tubules and absorption of calcium from the digested food.

The parathyroid glands secrete a peptide hormone called parathyroid hormone or parathormone (PTH). The release of parathromone is regulated by the circulating levels of calcium ($Ca^{2+}$) ions in the blood. PTH plays an important role in calcium balance of the body. It maintains the calcium balance between the blood and other tissues. When the calcium level in the blood decreases, parathyroid hormone is released in order to increase the calcium level in the blood. PTH acts on bones and other skeletal structure and mobilizes the calcium ($Ca^{2+}$) from the bones into the blood. This is called bone resorption/dissolution/demineralization. The parathromone also increases the reabsorption of calcium by the renal tubules and absorption of calcium from the digested food. Hence, parathormone induces increase in serum calcium.

The parathyroid gland secretes a peptide hormone called parathyroid hormone (PTH). The secretion of PTH is regulated by the circulating levels of calcium ions. PTH increases the calcium levels in the blood. PTH also stimulates reabsorption of calcium by the renal tubules and increase calcium absorption from the digested food.

The parathyroid gland was first discovered in 1852 during the autopsy of an Indian rhinoceros by Sir Richard Owen.

Parathyroid glands located behind the thyroid gland, produce a hormone called parathormone. This hormone maintains calcium and phosphorus balance in the body. Thus, if a person is having problem with calcium and phosphorus metabolism in the body, this means, his parathyroid glands are not functioning properly.

Parathyroid hormone regulates the level of calcium in the blood. It does this through its actions on the kidneys, bones and intestine. When  the blood calcium level is too low, the parathyroid glands release more parathyroid hormone (PTH). This causes the bones to release more calcium into the blood, increase the absorption of more calcium through food and reduces the amount of calcium released by the kidneys into the urine. 

Homeostasis is the process wherein normal body variables are actively regulated inside a defined environment to remain very near to constant. The regulation of  concentration of sodium ($Na^+$) and Calcium ($Ca^{++}$) ions in the blood as well as  glucose levels in blood plasma are examples of Homeostasis.
In the human body, the concentration of blood sugar levels is regulated by the  beta cells of the pancreatic islets by secreting insulin into the blood and inhibits the secretion of glucagon into the blood. The table given in the question shows the effect of a substance on the normal body variables after an intravenous injection of the same. According to the given data,  the  injection of substance A tends to decrease the concentration of Serum glucose below the baseline value. Hence, the substance that was injected is identified as insulin.