Thyroid Gland Questions in English

(D) The $Thyroid$ gland is unique among endocrine glands because it stores its hormones in an inactive form within the extracellular space of the thyroid follicles, known as the colloid.
These hormones, $Thyroxine$ $(T_4)$ and $Triiodothyronine$ $(T_3)$, are synthesized and stored as part of the protein $Thyroglobulin$ in the follicular lumen.
When the body requires these hormones, they are reabsorbed from the colloid into the follicular cells, processed, and then released into the bloodstream.

(A) The thyroid gland specifically absorbs iodine to synthesize thyroid hormones ($T_3$ and $T_4$).
Radioactive Iodine-$131$ $(^{131}I)$ is used in medical diagnostics and therapy because the thyroid gland concentrates it,allowing for the detection of cancerous cells or the destruction of overactive thyroid tissue.
Other isotopes like Carbon-$14$ are used for radiocarbon dating,Uranium-$238$ for geological dating,and Phosphorus-$32$ for molecular biology research.

(B) The thyroid gland secretes two main hormones: thyroxine $(T_4)$ and triiodothyronine $(T_3)$.
These hormones play a crucial role in regulating the basal metabolic rate $(BMR)$ of the body.
They also support the process of red blood cell formation,control the metabolism of carbohydrates,proteins,and fats,and maintain water and electrolyte balance.
Therefore,the correct answer is the thyroid gland.

(B) The deficiency of thyroxine in adults leads to a condition called $Myxoedema$.
Key characteristics of $Myxoedema$ include:
$1$. $A$ significantly low metabolic rate.
$2$. An increase in body weight due to metabolic slowdown.
$3$. $A$ tendency for tissues to retain water,leading to puffiness.
$Cretinism$ is caused by thyroid deficiency in children,while $Goitre$ is an enlargement of the thyroid gland often due to iodine deficiency. $Hypothyroidism$ is the general term for the underactive thyroid state,but $Myxoedema$ is the specific clinical term for the adult condition described.

(C) Goitrogens are substances that disrupt the production of thyroid hormones by interfering with iodine uptake in the thyroid gland.
When the synthesis of thyroxine $(T_4)$ is inhibited,the pituitary gland increases the secretion of Thyroid Stimulating Hormone $(TSH)$.
This constant stimulation of the thyroid gland leads to its enlargement,a condition known as simple goiter (or colloid goiter).
Therefore,the consumption of goitrogenic substances leads to the development of simple goiter.

(D) The correct match is $D$. The thyroid gland secretes thyroxine (or tetraiodothyronine). Iodine is an essential component for the synthesis of thyroid hormones. $A$ deficiency of iodine in the diet leads to hypothyroidism and enlargement of the thyroid gland,a condition known as goiter.
- Option $A$ is incorrect because the corpus luteum secretes progesterone,not testosterone.
- Option $B$ is incorrect because oxytocin is synthesized by the hypothalamus and released by the posterior pituitary,not the anterior pituitary.
- Option $C$ is incorrect because the growth hormone is secreted by the anterior pituitary,not the posterior pituitary.

(B) The symptoms described,such as stunted growth,mental retardation,low $IQ$,and abnormal skin,are characteristic of $Cretinism$.
$Cretinism$ is a condition caused by hypothyroidism during fetal development or early infancy.
Thyroid hormones ($T_3$ and $T_4$) are essential for the normal physical and mental development of a child.
Iodine is a crucial component for the synthesis of thyroid hormones.
If a pregnant woman has a deficiency of iodine in her diet,it leads to inadequate production of thyroid hormones,which affects the development of the fetus,resulting in $Cretinism$.

(D) Graves' disease,also known as exophthalmic goiter,is an autoimmune disorder.
It is caused by the hypersecretion of thyroid hormones ($T_3$ and $T_4$) by the thyroid gland.
Symptoms include enlargement of the thyroid gland,protrusion of the eyeballs (exophthalmos),increased basal metabolic rate,and weight loss.
Therefore,the correct option is $D$.

(A) The metamorphosis of a tadpole into an adult frog is regulated by the hormone thyroxine,which is secreted by the thyroid gland.
If the production of thyroxine is inhibited,the tadpole fails to undergo metamorphosis and continues to grow in size,eventually becoming a giant-sized tadpole.
Antithyroid substances,such as thiourea,inhibit the synthesis of thyroxine.
Therefore,administering thiourea prevents metamorphosis,allowing the tadpole to continue growing without transforming into an adult frog.

(A) The thyroid gland secretes a hormone known as thyroxine $(T_4)$.
Thyroxine is an iodinated derivative of the amino acid tyrosine,meaning it contains iodine atoms in its structure.
Iodine is essential for the synthesis of thyroid hormones.
$A$ deficiency of iodine in the diet leads to a decrease in the production of thyroxine,which can cause the thyroid gland to enlarge,a condition known as goitre.

(A) Calcitonin (or thyrocalcitonin) is secreted by the parafollicular cells of the thyroid gland. It lowers blood calcium levels by inhibiting bone resorption and promoting calcium excretion in urine.
Parathormone $(PTH)$ is secreted by the chief cells of the parathyroid gland. It increases blood calcium levels by stimulating calcium absorption from the intestine,reabsorption from the renal tubules,and bone demineralization.
Since calcitonin lowers blood calcium and parathormone raises it,they have antagonistic effects.
Therefore,the Assertion is correct,the Reason is correct,and the Reason is the correct explanation of the Assertion.

(N/A) Diabetes mellitus is characterized by abnormally high glucose levels in the blood due to the deficiency of the hormone insulin.
$(b)$ Goiter is characterized by an abnormal enlargement of the thyroid gland due to the deficiency of thyroxine hormone in the body.
$(c)$ Cretinism is characterized by stunted growth and mental retardation in children due to the deficiency of thyroid hormones during fetal development or early infancy.

(N/A) Location: The thyroid gland is composed of two lobes which are located on either side of the trachea.
Both the lobes are interconnected with a thin flap of connective tissue called the isthmus.
Structure: The thyroid gland is composed of follicles and stromal tissues. Each thyroid follicle is composed of follicular cells,enclosing a cavity.
These follicular cells synthesize two hormones,tetraiodothyronine or thyroxine $(T_{4})$ and triiodothyronine $(T_{3})$.
Iodine is essential for the normal rate of hormone synthesis in the thyroid.
Deficiency of iodine in our diet results in hypothyroidism and enlargement of the thyroid gland,commonly called goitre.
Symptoms of goitre include stunted growth (cretinism),mental retardation,low intelligence quotient,abnormal skin,deaf-mutism,etc. Hypothyroidism during pregnancy causes defective development and maturation of the growing body.
In adult women,hypothyroidism may cause the menstrual cycle to become irregular.
Due to cancer of the thyroid gland or due to the development of nodules of the thyroid glands,the rate of synthesis and secretion of the thyroid hormones is increased to abnormally high levels,leading to a condition called hyperthyroidism,which adversely affects body physiology.
Functions:
$(i)$ Thyroid hormones play an important role in the regulation of the Basal Metabolic Rate $(BMR)$.
$(ii)$ They support the process of Red Blood Cell $(RBC)$ formation.
$(iii)$ Thyroid hormones control the metabolism of carbohydrates,proteins,and fats.
$(iv)$ Maintenance of water and electrolyte balance is also influenced by thyroid hormones.
$(v)$ The thyroid gland also secretes a protein hormone called thyrocalcitonin $(TCT)$,which regulates blood calcium levels.

(N/A) The thyroid gland is located on either side of the trachea and consists of two lobes interconnected by a thin flap of connective tissue called the isthmus. It is composed of follicles and stromal tissues. The follicular cells synthesize two hormones: tetraiodothyronine or thyroxine $(T_4)$ and triiodothyronine $(T_3)$. Iodine is essential for the normal rate of hormone synthesis.
$1$. Hypothyroidism: Deficiency of iodine in our diet leads to hypothyroidism and enlargement of the thyroid gland,commonly called goitre. Symptoms include stunted growth (cretinism),mental retardation,low intelligence quotient,abnormal skin,and deaf-mutism. Hypothyroidism during pregnancy causes defective development and maturation of the growing baby. In adult women,it may cause irregular menstrual cycles.
$2$. Hyperthyroidism: This condition occurs due to cancer of the thyroid gland or the development of nodules,which increases the synthesis and secretion of thyroid hormones to abnormally high levels,adversely affecting body physiology.
$3$. Graves' Disease (Exophthalmic Goitre): This is a form of hyperthyroidism characterized by the enlargement of the thyroid gland,protrusion of the eyeballs,increased basal metabolic rate,and weight loss.

(N/A) The endocrine gland that produces calcitonin is the thyroid gland,specifically the parafollicular cells (also known as $C$-cells).
Calcitonin plays a crucial role in calcium homeostasis by lowering blood calcium levels.
It inhibits the activity of osteoclasts,thereby reducing the resorption (dissociation) of $Ca^{++}$ and phosphate from the bones into the blood.

(N/A) The two primary hormones responsible for regulating $Ca^{++}$ levels in the blood are Parathyroid hormone $(PTH)$ and Calcitonin.
$PTH$ is secreted by the parathyroid gland and acts to increase blood $Ca^{++}$ levels. It stimulates bone resorption (demineralization),increases $Ca^{++}$ reabsorption by renal tubules,and enhances $Ca^{++}$ absorption from digested food in the intestine.
Calcitonin is produced by the parafollicular cells ($C$-cells) of the thyroid gland. It acts antagonistically to $PTH$ by lowering blood $Ca^{++}$ levels,primarily by inhibiting bone resorption.

(A) These people are likely suffering from goitre,which is characterized by a swollen neck.
$(b)$ Goitre is caused by a deficiency of iodine in the diet. Iodine is essential for the synthesis of thyroid hormones,$T_{3}$ (triiodothyronine) and $T_{4}$ (thyroxine). When iodine levels are low,the thyroid gland enlarges in an attempt to produce more hormones,leading to hypothyroidism.
$(c)$ During pregnancy,maternal hypothyroidism can severely affect the developing foetus. It may lead to cretinism,which is characterized by stunted growth,mental retardation,low intelligence quotient,abnormal skin,and deaf-mutism.

(B) Hypothyroidism during pregnancy leads to a deficiency of thyroid hormones in the developing foetus.
This condition results in stunted growth,a condition known as cretinism.
It also causes mental retardation,low intelligence quotient,abnormal skin texture,and deaf-mutism in the growing baby.

(N/A) Hypothyroidism: This condition is caused by the under-secretion of thyroid hormones. In children,it leads to cretinism,characterized by retarded physical and mental growth,short limbs,a protruding tongue,and dry skin. In adults,it causes myxedema,which is more common in females and is characterized by an abnormal metabolic rate and rough,dry skin.
Hyperthyroidism: This condition is caused by the over-secretion of thyroid hormones ($T_3$ and $T_4$). It leads to Grave's disease,which includes symptoms like an increased metabolic rate,weight loss,and nervousness. Exophthalmic goitre (protrusion of eyeballs) is often observed in adults. Toxic goitre,also known as Plummer's disease,occurs due to the excessive production of thyroxine.

(N/A) The thyroid gland is composed of two lobes which are located on either side of the trachea. Both these lobes are interconnected with a thin flap of connective tissue called the Isthmus.

(A) The thyroid gland is composed of follicles and stromal tissues. Each thyroid follicle is composed of follicular cells,enclosing a cavity. These follicular cells synthesize two hormones: tetraiodothyronine or thyroxine $(T_4)$ and triiodothyronine $(T_3)$.

(B) Goitre is an enlargement of the thyroid gland,often caused by iodine deficiency.
Symptoms associated with hypothyroidism (which often leads to goitre) include stunted growth (cretinism),mental retardation,low intelligence quotient $(IQ)$,abnormal skin,and deaf-mutism.
Hypothyroidism during pregnancy causes defective development and maturation of the growing fetus.

(D) Exophthalmic goitre,also known as Graves' disease,is a form of hyperthyroidism caused by the overproduction of thyroid hormones.
Its primary symptoms include:
$1$. Enlargement of the thyroid gland (goitre).
$2$. Protrusion of the eyeballs (exophthalmos).
$3$. Increased basal metabolic rate $(BMR)$.
$4$. Weight loss despite increased appetite.
$5$. Rapid heartbeat and nervousness.

(B) The hormone $Thyroxine$ is secreted by the thyroid gland.
$Thyroxine$ is essential for the process of metamorphosis in a tadpole,which transforms it into an adult frog.
Without sufficient iodine in the water,the thyroid gland cannot produce enough $Thyroxine$,and the tadpole will fail to undergo metamorphosis.

(A) Thyroxine,also known as $T_4$,is a hormone produced by the thyroid gland.
Its chemical structure contains four iodine atoms,as shown in the provided image.
Iodine is an essential component for the synthesis of thyroid hormones.
Insulin is a peptide hormone,testosterone is a steroid hormone,and adrenaline is an amino acid derivative (catecholamine),none of which contain iodine.

(A) $BMR$ (Basal Metabolic Rate) of an organism is the minimum rate of energy conversion required just to stay alive during complete rest or sleep.
$BMR$ is primarily regulated by the thyroxine hormone,which is secreted by the thyroid gland.
Thyroxine increases the rate of cellular respiration and metabolic activities in the body,thereby maintaining the basal metabolic rate.

(D) $Myxoedema$ is caused due to the under-secretion of thyroid hormones in adults.
It is also known as $Gull's$ disease.
It is characterized by a puffy appearance due to the subcutaneous accumulation of fat, low $BMR$ (Basal Metabolic Rate), and a decreased heart rate.

(B) Hypothyroidism during pregnancy causes defective development and maturation of the growing baby,leading to stunted growth (cretinism),mental retardation,low intelligence quotient,abnormal skin,and deaf-mutism.
In adult women,hypothyroidism may cause the menstrual cycle to become irregular.

(D) The thyroid gland is composed of two lobes,which are located on either side of the trachea. Both the lobes are interconnected with a thin flap of connective tissue called the isthmus. Therefore,the statement that the thyroid consists of four lobes is incorrect.

(B) Calcitonin,also known as Thyrocalcitonin $(TCT)$,is a peptide hormone.
$1$. It is non-iodised,distinguishing it from the thyroid hormones $T_3$ and $T_4$.
$2$. It is secreted by the parafollicular cells (also called $C$-cells) of the thyroid gland.
$3$. It regulates the calcium level in the blood by lowering it,hence it is a hypocalcemic hormone.
$4$. It is correctly referred to as $TCT$ (Thyrocalcitonin).
$5$. It is $NOT$ a hyperglycemic agent; it has no role in glucose metabolism. Hyperglycemic agents increase blood glucose levels (e.g.,glucagon).
Therefore,statements $I, II, III$,and $IV$ are correct.

(A) The functions listed correspond to the thyroid gland:
$1.$ Regulation of $BMR$ (Basal Metabolic Rate).
$2.$ Supports the process of $RBC$ (Red Blood Cell) formation (erythropoiesis).
$3.$ Controls the metabolism of carbohydrates,proteins,and fats.
$4.$ Maintenance of water and electrolyte balance.
$5.$ Secretion of $TCT$ (Thyrocalcitonin) hormone,which regulates blood calcium levels.
Therefore,the correct option is $A$.

(B) Iodine is essential for the normal rate of hormone synthesis in the thyroid gland.
Deficiency of iodine in our diet results in hypothyroidism (low production of thyroid hormones) and enlargement of the thyroid gland,a condition commonly called goitre.
Therefore,the correct combination is $A-Iodine, B-hypothyroidism, C-goitre$.

(C) The thyroid gland is the largest endocrine gland in the human body. It is located in the neck,anterior to the thyroid cartilage.

(C) The thyroid gland is a bilobed endocrine gland located on either side of the trachea in the neck region.
These two lobes are connected by a thin flap of connective tissue known as the isthmus.
Therefore, $A = 2$ (lobes), $B = \text{trachea}$, and $C = \text{isthmus}$.
The correct combination is $A-2, B-\text{trachea}, C-\text{isthmus}$.

(D) $I.$ Hypothyroidism (low thyroid hormone levels) can lead to menstrual irregularities in women.
$II.$ Hyperthyroidism (excessive thyroid hormone levels) increases metabolic rate and adversely affects body physiology.
$III.$ Hypothyroidism during pregnancy causes defective development and maturation of the growing baby,leading to stunted growth (cretinism).
$IV.$ Hypothyroidism,often due to iodine deficiency,leads to the enlargement of the thyroid gland,a condition known as goitre.
Since all the given statements are scientifically correct,the correct option is $D$.

(C) Thyroxine: This hormone maintains the $BMR$ (Basal Metabolic Rate),regulates the metabolism of carbohydrates,proteins,and fats,and supports the process of erythropoiesis (red blood cell formation).
Adrenaline: This hormone is released during stress and initiates the 'fight or flight' response.
Thymine: This is a nitrogenous base found in $DNA$,not a hormone.
Thymosin: This is a hormone secreted by the thymus gland that plays a major role in the differentiation of $T$-lymphocytes,which provide cell-mediated immunity.

(D) Cretinism is a condition characterized by stunted physical growth and mental retardation,which is caused by a deficiency of thyroid hormones during fetal development or early childhood.
Since the thyroid gland fails to secrete adequate amounts of thyroid hormones,the administration of $Thyroxine$ (a thyroid hormone) can prevent or treat this condition by restoring normal hormone levels in the body.

(A) Parathyroid glands (four in number) are present on the dorsal surface of the thyroid gland.
The thyroid gland secretes thyroxine (tetraiodothyronine) and triiodothyronine,which play a crucial role in regulating the basal metabolic rate $(BMR)$ and the metabolism of proteins,fats,and carbohydrates.
Therefore,$X$ is the parathyroid gland and $Y$ is the thyroid gland.

(A) The thyroid gland is the largest endocrine gland in the human body. It is located in the neck,anterior to the thyroid cartilage,and is responsible for producing hormones like thyroxine $(T_4)$ and triiodothyronine $(T_3)$,which regulate the body's metabolic rate.

(B) Failure of thyroid secretion from infancy leads to a condition known as $Cretinism$,which is characterized by stunted growth $(dwarfism)$,mental retardation,low intelligence quotient,abnormal skin,and deaf-mutism.
In contrast,the deficiency of thyroid hormone in adults causes $Myxoedema$ (also known as $Gull's$ disease),which is characterized by swelling of the face and hands.

(A) The thyroid gland is composed of two types of cells: follicular cells and parafollicular cells (also known as $C$-cells).
Follicular cells secrete iodinated hormones like thyroxine $(T_4)$ and triiodothyronine $(T_3)$.
Parafollicular cells secrete a peptide hormone called calcitonin,which is non-iodinised.
Calcitonin plays a role in calcium homeostasis by lowering blood calcium levels.
Oxytocin,Vasopressin,and Gonadotrophins are hormones associated with the hypothalamus and pituitary gland,not the thyroid gland.

(B) Cretinism is caused by the deficiency of thyroid hormones (hypothyroidism) during fetal development or early childhood.
Key symptoms include stunted growth,mental retardation,low intelligence quotient $(IQ)$,abnormal skin,deaf-mutism,pot-bellied abdomen,pigeon-like chest,and a protruding tongue.
Myxoedema is caused by thyroid hormone deficiency in adults,characterized by puffy appearance and lack of alertness.
Cushing's Syndrome is caused by the oversecretion of cortisol,leading to obesity and muscle wasting.
Addison's disease is caused by the undersecretion of hormones from the adrenal cortex,leading to skin pigmentation and weakness.

(A) Cretinism is caused by the hyposecretion of $Thyroxine$ (thyroid hormone) during early childhood.
This condition is characterized by stunted physical growth,mental retardation,low intelligence quotient,abnormal skin,and deaf-mutism.

(A) Thyroxine shows a calorigenic effect because it increases the rate of catabolism in the body.
This process leads to the production of energy and an increase in body temperature.
The mechanism involves increased oxygen consumption and higher rates of $ATP$ hydrolysis,which releases heat as a byproduct.

(B) The $Thyroid$ gland is the primary site for the storage of iodine in the human body.
Iodine is an essential trace element required for the synthesis of thyroid hormones,specifically $Thyroxine$ $(T_4)$ and $Triiodothyronine$ $(T_3)$.
The $Thyroid$ gland actively traps iodide ions from the blood and incorporates them into the protein $Thyroglobulin$ to produce these hormones.
Therefore,the correct option is $B$.

(D) The thyroid gland secretes hormones like thyroxine $(T_4)$ and triiodothyronine $(T_3)$.
These hormones play a crucial role in regulating the basal metabolic rate $(BMR)$ of the body.
They also support the process of red blood cell formation and control the metabolism of carbohydrates,proteins,and fats.
Therefore,the correct answer is the thyroid gland.

(C) Hypothyroidism in children leads to a condition known as cretinism.
Symptoms of cretinism include stunted growth,mental retardation,low intelligence quotient,abnormal skin,and deaf-mutism.
Exophthalmos (protrusion of eyeballs) is a characteristic symptom of hyperthyroidism (specifically Graves' disease),not hypothyroidism.
Therefore,the correct option is $C$.

(B) The thyroid gland is the largest endocrine gland in the human body.
It is composed of two lobes which are located on either side of the trachea (windpipe).
These lobes are interconnected with a thin flap of connective tissue called the isthmus.

(C) Hyperthyroidism is a condition caused by the over-secretion of thyroid hormones ($T_3$ and $T_4$).
Graves' disease is a form of hyperthyroidism characterized by an enlarged thyroid gland,protrusion of the eyeballs (exophthalmos),increased basal metabolic rate,and weight loss.
Cretinism is caused by hypothyroidism in children.
Goitre is typically associated with iodine deficiency (hypothyroidism).
Addison's disease is caused by the under-secretion of hormones from the adrenal cortex.