This set of Molecular Endocrinology Multiple Choice Questions & Answers (MCQs) focuses on “Parathyroid Gland and their Hormones – Parathormone”.
1. Which endocrine gland synthesizes parathormone?
a) Parathyroid gland
b) Thyroid gland
c) Pancreas
d) Liver
View Answer
Explanation: Parathormone is synthesized by parathyroid cells. Parathyroid glands are related to the control of the blood plasma concentration of calcium and phosphate ions. Parathyroid glands are four tiny endocrine system glands that regulate the calcium in our bodies.
2. What are the two major functions of parathormone?
a) Increase phosphate ion and decrease calcium ion concentrations
b) Increase the concentration of calcium and decrease the concentration of phosphorus
c) Regulation of thyroid gland and hormone release
d) Increase the concentration of calcium and phosphorus
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Explanation: The major two functions of parathormone is to increase the concentration of calcium and reduce the concentration of phosphorus. Parathormone also regulates the renal release of calcium and phosphate ions.
3. How many amino acids are present in parathormone?
a) 34
b) 31
c) 84
d) 81
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Explanation: Parathormone is a linear polypeptide that is made up of 84 amino acids in total. Alanine is the n-terminal amino acid and glutamine is the amino acid present in the C-terminal. It acts to increase the concentration of calcium in the blood, while calcitonin (a hormone produced by thyroid gland parafollicular cells) acts to reduce the concentration of calcium.
4. PTH (Parathormone) is initially synthesized as a prohormone in the chief cells.
a) True
b) False
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Explanation: Initially, PTH is synthesized as a prohormone in the chief cells. In polysomes, Pre-Pro-PTH, consisting of 115 amino acids, is first formed, sticking to the rough ER membrane. One of the two cell groups of the parathyroid glands, along with oxyphil cells, is the parathyroid chief cells (also called parathyroid principal cells or simply parathyroid cells).
5. Primary hyperthyroidism is related to positive magnesium balance.
a) True
b) False
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Explanation: It has been observed that PTH regulates the metabolism of Mg. It has been observed that primary hyperparathyroidism is linked with abnormal urinary excretion of Mg and negative Mg balance. A deficiency of magnesium can increase the risk of developing Hashimoto’s disease and is associated with increased levels of thyroid antibodies.
6. Which amino acid is very essential for the calcium regulatory mechanism of parathormone?
a) Valine
b) Methionine
c) Alanine
d) Leucine
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Explanation: Methionine is an important amino acid that is essential for the mobilizing effect of calcium. The N-terminal end of up to 34 amino acids of parathormone has the receptor-binding mechanism. Types of biologically active bovine parathyroid hormone N-terminal fragment oxidisies at methionine 8 and methionine 18.
7. Which enzyme is involved in the conversion of pro parathormone to active parathormone?
a) Clipase B
b) Hydrolases
c) Acetylases B
d) Lyase B
View Answer
Explanation: The N terminal amino acids of PTH (parathormone) are hydrolyzed by a “trypsin-like” enzyme called Clipase B and then 6 amino acids (hexapeptide) are removed. As a result, Pro-PTH is converted to PTH.
8. Which are the two factors that stimulate the release of parathormone (PTH) from its vesicles?
a) Increased cAMP levels and decreased calcium levels
b) Increased calcium levels and decreased cAMP levels
c) Increased cAMP and calcium levels
d) Decreased levels of cAMP and calcium
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Explanation: PTH release from secretory vesicles is induced by increased c-AMP concentration and a low calcium level. However, despite its release, a high concentration of calcium induces the degradation of the deposited PTH in secretory vesicles.
9. What is the role of parathormone in vitamin D metabolism in the renal tissues?
a) Activates vitamin D
b) Deactivates vitamin D
c) Helps in the storage of vitamin D
d) Helps in the cleavage and breakdown of vitamin D
View Answer
Explanation: In the renal tissue, parathormone activates Vit D. This raises the conversion rate of 25-OH-cholecalciferol to 1,25-di-OH-cholecalciferol by triggering the enzyme alpha-1-hydroxylase. There is a well-established inverse relationship between serum 25-hydroxyvitamin D and serum parathyroid hormone (PTH), up to a certain level of 25-hydroxyvitamin D, where there is no further decrease in serum PTH.
10. Which among the following is one of the major activities of PTH on bones?
a) Osteoporosis
b) Osteoclastic osteolysis
c) Otosclerosis
d) Osteomalacia
View Answer
Explanation: Through the “second messenger” c-AMP, PTH stimulates osteoclasts to increase bone reabsorption, which improves the mobilization of Ca and P from the bones. This is known as the process of Osteoclastic osteolysis.
11. Which molecule is otherwise known as the Humoral hypercalcemic factor of malignancy (HHFM)?
a) PTHrP
b) LSH
c) PTH
d) FSH
View Answer
Explanation: The humoral hypercalcemic factor of malignancy (HHFM) is PTHrP (Parathormone-related Peptide). It is a peptide with 141 amino acids inside it. A protein part of the parathyroid hormone family secreted by mesenchymal stem cells is the parathyroid hormone-related protein (or PTHrP).
12. Which among the following can mimic the activities of PTH (Parathormone)?
a) FSH
b) LH
c) PTHrP
d) Calcitonin
View Answer
Explanation: PTHrP (Parathormone-related Peptide) can bind to the receptor and mimic the action of the parathormone (PTH). Several tumors, specifically squamous cell carcinomas of the lungs, produce this peptide.
13. Why PTH (Parathormone) is not able to act directly on intestinal mucosa cells?
a) PTH is inactive in intestinal mucosa cells
b) PTH is blocked by certain proteins in the intestinal mucosa cells
c) PTH is cleaved by certain enzymes on the cell surface receptors
d) Intestinal mucosa cells do not contain receptors for PTH
View Answer
Explanation: As the cells do not have specific receptors for PTH, PTH cannot act directly on intestinal mucosal cells. However, it increases the absorption of calcium and phosphate by producing 1-25, di-OH-cholecalciferol. Facilitating the absorption of calcium from the small intestine would clearly help to increase calcium levels in the blood.
14. What is responsible for the HHM (humoral hypercalcemia of malignancy) effect in malignant patients?
a) High serum PTHrP levels
b) Low serum PTHrP levels
c) High PTH serum levels
d) Low PTH serum levels
View Answer
Explanation: In normal healthy individuals and patients with primary hyperparathyroidism, serum PTHrP levels are low or absent. But in most malignancy patients, it is high and is responsible for HHM (humoral malignancy hypercalcemia).
15. How does PTH bring out the hypercalcemic effect in renal tissues?
a) By increasing serum phosphate levels
b) By reducing serum magnesium levels
c) By mobilizing calcium
d) By increasing serum calcium levels
View Answer
Explanation: By increasing the c-AMP second messenger, PTH carries out its functions. The drop in the level of serum inorganic phosphate by the action of PTH leads to bone mobilization of phosphate, which also mobilizes calcium, resulting in hypercalcemia.
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