Thyroid Gland & Parathyroid - Free MCQ Practice Test with solutions, NEET

Thyrocalcitonin also known as calcitonin is a polypeptide hormone secreted by the parafollicular or C cells of the thyroid gland. It lowers the levels of calcium and phosphate in the blood and promotes the formation of bone. Thus, the correct answer is option A.

Correct Answer: C. The Assertion is correct, but the Reason is incorrect.

Explanation:

• Assertion: Parathyroid hormone (PTH) indeed increases blood calcium levels by promoting bone resorption, enhancing calcium reabsorption in the kidneys, and increasing calcium absorption from the digestive tract. This is consistent with the physiological role of PTH in maintaining calcium homeostasis.

• Reason: The reason given is incorrect because PTH does not decrease blood calcium levels; rather, it increases them. The actions of PTH are aimed at raising calcium levels, not lowering them. Therefore, the Reason does not correctly explain the Assertion.

The correct answer is B: Thyroid.

- The thyroid gland plays a crucial role in regulating the basal metabolic rate (BMR) in body cells.
- Thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3), control metabolism by influencing the body's energy production and consumption.
- These hormones affect how quickly cells use energy and produce proteins, impacting the body's overall metabolic rate.
- An imbalance in thyroid hormone levels can lead to either an increased (hyperthyroidism) or decreased (hypothyroidism) metabolic rate.

Exophthalmic goitre is an endocrine disorder that is the most common cause of hyperthyroidism (excess secretion of thyroid hormone) and thyrotoxicosis (effects of excess thyroid hormone action in tissue). In this disease the excessive secretion of thyroid hormone is accompanied by diffuse enlargement of the thyroid gland.

Correct Answer: C. Option C is correct.

Explanation:

• Thyroxine (T4): This hormone supports metabolism and regulates the basal metabolic rate but is not directly related to increasing blood calcium levels. (Option A is incorrect.)

• Hypothyroidism: This condition is often associated with symptoms such as goitre (due to iodine deficiency) and stunted growth, not with exophthalmic goitre or weight loss. (Option B is incorrect.)

• Triiodothyronine (T3): This hormone is crucial for regulating the basal metabolic rate and supporting various metabolic processes. (Option C is correct.)

• Graves’ Disease: This is a form of hyperthyroidism characterized by an increased metabolic rate and protrusion of the eyeballs, not by iodine deficiency. (Option D is incorrect.)

Correct option: B

Myxoedema is the characteristic manifestation of severe hypothyroidism in adults; it results from accumulation of glycosaminoglycans in the dermis and subcutaneous tissues, producing non-pitting oedema.

Patients often have features such as weight gain, cold intolerance, bradycardia, dry coarse skin and slowed mental activity, in addition to the described non-pitting oedema.

Addison's disease is primary adrenal insufficiency and is not caused by hypothyroidism.

Cretinism refers to congenital or early childhood hypothyroidism with growth and neurodevelopmental impairment; it is not a consequence of adult hypothyroidism.

Sterility or infertility can be associated with hypothyroidism because of menstrual disturbances, but it is not the classical defining consequence asked for here and is not the single best answer.

Therefore, the single best answer is Myxoedema (option B).

The hormone calcitonin, which is produced by the parafollicular (or C) cells of the thyroid, has the opposite effect on blood calcium levels as PTH. Calcitonin decreases blood calcium levels by inhibiting osteoclasts, stimulating osteoblasts, and stimulating calcium excretion by the kidneys. Hence, Option C.

Correct Answer: C. The Assertion is correct, but the Reason is incorrect.

Explanation: Exophthalmic goitre (Graves' disease) is indeed characterized by protrusion of the eyeballs and an increased basal metabolic rate. However, hyperthyroidism causes an increased basal metabolic rate, not a decreased one, and it is associated with weight loss, not weight gain. Therefore, the Assertion is correct, but the Reason is incorrect.

- Acromegaly is the disease not related to the thyroid glands.
- Cretinism: Linked to thyroid hormone deficiency during infancy, leading to stunted growth and intellectual disability.
- Myxoedema: Results from severe hypothyroidism in adults, causing swelling, fatigue, and mental sluggishness.
- Goitre: Enlargement of the thyroid gland often due to iodine deficiency.
- Acromegaly: Caused by excess growth hormone post-puberty, leading to enlarged bones and tissues.

The correct answer is D: Basal metabolic rate.

- The thyroid gland primarily regulates the body's metabolism through the production of thyroid hormones.
- Thyroid hormones, like T3 and T4, play a crucial role in controlling the basal metabolic rate (BMR).
- BMR is the amount of energy expended while at rest, necessary for functions like breathing, circulating blood, and maintaining body temperature.
- Proper thyroid function ensures the body's metabolism operates at an optimal level, influencing weight, energy levels, and overall health.

Hypersecretion of parathyroid hormone (PTH) increases serum calcium levels via enhanced bone resorption and renal calcium reabsorption. Due to hypersecretion of parathyroid the bones becomes weaker.

Thyroxine is the main hormone produced by the thyroid gland which controls the body's basal metabolic rate (BMR).  Every cell in the body depends on thyroid hormones for proper metabolism. Too much thyroxine causes a BMR, that is too high. This leads to Graves' disease, a condition pertaining to an overactive thyroid.

The correct answer is: D: Parathyroid gland

- The parathyroid glands are small endocrine glands located behind the thyroid gland.
- There are typically four parathyroid glands in humans.
- These glands are responsible for regulating calcium levels in the blood by secreting parathyroid hormone (PTH).
- PTH helps to increase blood calcium levels by acting on the bones, kidneys, and intestines.
- Proper calcium levels are essential for nerve function, muscle contraction, and bone health.

Cretinism is due to abnormal secretion of thyroxine.

Cretinism is caused by the hypersecretion of thyroid hormone in infants called thyroxine. Thyroxine has markedly reduced metabolic rate and oxidation. This leads to slow heartbeat , lower blood pressure , decrease in body temperature , stunted growth , etc. The disorder can be created by an early administration of thyroid hormones .

The Thyroid gland is the only endocrine gland that stores its secretory product in large quantities, normally about 10 days supplies in the extracellular space before discharging into the blood. It secretes iodinated hormone i.e., thyroxine and triiodothyronine that are stored in the colloid which fills the follicle cells and released to blood when needed.

The basal metabolic rate is regulated significantly by thyroid hormones, which also contribute to red blood cell formation. These hormones play a crucial role in overseeing the metabolism of carbohydrates, proteins, and fats. Additionally, thyroid hormones impact the maintenance of water and electrolyte balance. The thyroid gland also produces thyrocalcitonin (TCT), a protein hormone that plays a role in regulating blood calcium levels.

Thyroxine increases the number and activity of mitochondria in cells by binding to the cells' DNA, increasing the basal metabolic rate. Administration of thyroid hormones, such as thyroxine, causes an increase in the rate of carbohydrate and fat metabolism and a rise in the rate of protein synthesis and breakdown.

Goitre is a pathological condition associated with Thyroxine.

- Thyroxine, a hormone produced by the thyroid gland, regulates metabolism.
- When the thyroid gland doesn't produce enough thyroxine, it can lead to Goitre.
- Goitre is an enlargement of the thyroid gland, often due to iodine deficiency or thyroid disorders.
- Thyroxine imbalance can disrupt the feedback loop controlling thyroid hormone production.
- Correcting thyroxine levels through medication or iodine supplementation can treat Goitre effectively.

Parathormone of parathyroid gland increases the blood calcium level. Removal of parathyroid gland decreases the blood calcium level due to its increased excretion in urine. It causes increased excitability of muscles and their sustained contraction referred to as parathyroid tetany. Myxedema is caused by hypothyroidism in adults while Addison’s disease is caused by the presence of ineffective ACTH. Simmond's disease is caused by the destruction of the anterior pituitary lobe. Thus, the correct answer is A.

T₃ is less tightly bound to plasma proteins than is T₄ and is therefore more readily available for cellular uptake. T₃ binds to nuclear receptors to a much greater extent than T₄, hence T₃ is more rapidly and biologically active than T₄. T₃ and T4 are deiodinated and deaminated in the tissues.

:- Thyroid (ii): The thyroid gland secretes calcitonin, which helps regulate calcium levels in the blood.
- Parathyroid (iv): The parathyroid glands produce parathyroid hormone (PTH), which regulates calcium and phosphorus levels in the blood.

These two glands work together to maintain the balance of calcium and phosphorus in the body, crucial for proper bone health and nerve function.Parathyroid hormone, or PTH, is secreted by the parathyroid glands and increases blood levels of calcium by stimulating bones to release calcium, stimulating kidney cells to reclaim calcium from urine before excretion, and increasing calcium absorption by the intestine.

Correct option: B

Parathormone (PTH) is secreted by the parathyroid glands and its net effect is to increase blood calcium concentration.

PTH raises blood calcium by three main actions: it stimulates bone resorption by increasing the activity of osteoclasts, it increases renal reabsorption of Ca²⁺ in the kidney, and it promotes activation of 1,25-dihydroxyvitamin D (calcitriol) which increases intestinal absorption of calcium.

Deficiency of PTH therefore causes a fall in blood calcium, i.e., hypocalcaemia, which may produce features such as tetany, muscle cramps and paraesthesia.

Hypercalcaemia is caused by excess PTH (hyperparathyroidism), not by PTH deficiency. Goitre is related to the thyroid gland and iodine deficiency, and is not caused by parathormone deficiency.

Hence the correct answer is Hypocalcaemia (option B).