Question

The hormone that increases the blood calcium level and decreases its excretion by the kidney is
A. Parathormone
B. Calcitonin
C. Thyroxine
D. Insulin

Answer 1

Hint: Hormones are chemical messengers secreted from special glands in the body. The glands are known as ductless or endocrine glands which secrete the hormones directly into the bloodstream. Endocrine glands of the body include thyroid gland, pancreas, pituitary gland, etc. Hormones bring about a lot of functions in the body like controlling sugar levels, calcium levels, growth, metabolism, etc.

Complete answer:
Parathormone or Parathyroid hormone is secreted from the parathyroid gland present in the neck of human beings. Parathormone is involved in calcium regulation of the body. Calcium is required in our body for structuring of the bones, clotting of blood, contraction of muscles. The bone tissues are resorbed and rebuilt with time. Parathyroid hormone influences the resorption of bones to increase the calcium level in blood.
In the kidneys, parathormone influences the kidney tubules and the collecting ducts to reabsorb calcium into the bloodstream. Therefore, it can be said that parathormone increases excretion of calcium through urine.
Another way by which parathormone increases blood calcium level is by inhibiting the uptake of phosphate ions from the kidney tubules. Phosphate ions combine with calcium and form salts. Decrease in phosphate concentration leads to increased ionization of calcium. This results in an increased level of calcium in the blood.
Calcitonin is secreted by the parafollicular cells present in the thyroid gland. The function of calcitonin is reverse of the function of parathormone. In other words, calcitonin serves to decrease the concentration of calcium in blood.
Thyroxine is secreted by the thyroid gland. It helps the body to regulate metabolism, protein synthesis and growth. It does not play any role in calcium regulation of the body.
Insulin is secreted by the cells of Islet of Langerhans of the pancreas. Insulin helps to reduce the level of blood sugar. Insulin is a peptide hormone. Insulin is an anabolic hormone that facilitates uptake of sugar by the liver and its subsequent conversion into glycogen. Insulin does not have any role in calcium regulation of our body.
Therefore, it can be concluded that parathormone increases concentration of calcium in the blood and decreases its excretion from the body.

Hence, option (A) is correct.
Note: Hormones are secretions of endocrine glands that are secreted in the blood. Hormones affect a lot of bodily functions like metabolism, growth, regulation of blood glucose, etc. Parathyroid gland is an endocrine gland that secretes parathormone. Parathormone serves to regulate blood calcium levels through bone resorption, decreasing its excretion by the kidney.