Thyroid Gland Questions in English

(D) The $BMR$ (Basal Metabolic Rate) is primarily regulated by the thyroid hormones,specifically $T_4$ (Thyroxine) and $T_3$ (Triiodothyronine).
These hormones increase the rate of cellular respiration and oxygen consumption in most tissues of the body,thereby increasing the $BMR$.
While adrenaline can cause a temporary increase in metabolic rate,thyroxine is the primary hormone responsible for maintaining and regulating the basal metabolic rate over the long term.

(D) The thyroid gland in higher vertebrates is phylogenetically homologous to the $Endostyle$ found in lower chordates like $Urochordates$ (e.g.,$Herdmania$) and $Cephalochordates$ (e.g.,$Amphioxus$).
Both structures are involved in iodine metabolism and the secretion of iodinated proteins.

(C) 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 help in maintaining body temperature by influencing metabolic processes and heat production.
Therefore,the correct option is $C$.

(A) Metamorphosis in amphibians,such as the transformation of a tadpole into an adult frog,is regulated by the thyroid hormone known as $Thyroxine$.
If the thyroid gland is removed or if iodine is deficient in the water,the tadpole fails to undergo metamorphosis and remains in the larval stage.
Therefore,$Thyroxine$ is the hormone responsible for accelerating the process of metamorphosis in frogs.

(A) Thyrocalcitonin $(TCT)$ is a protein hormone secreted by the thyroid gland.
Its primary function is to regulate blood calcium levels.
When the concentration of calcium ions in the blood increases (hypercalcemia),the thyroid gland releases $TCT$.
$TCT$ acts to lower the blood calcium level by inhibiting bone resorption (the breakdown of bone tissue) and promoting calcium deposition in the bones.

(B) Hashimoto's disease, also known as chronic lymphocytic thyroiditis, is an autoimmune disorder. In this condition, the immune system produces antibodies that attack and destroy the cells of the thyroid gland. This leads to hypothyroidism, as the gland becomes unable to produce sufficient thyroid hormones.

(D) Thyroid hormones,specifically $T_3$ (triiodothyronine) and $T_4$ (thyroxine),play a crucial role in regulating the basal metabolic rate $(BMR)$ of the body.
They stimulate the metabolic processes of all three major macronutrients:
$1$. They promote protein synthesis and increase protein metabolism.
$2$. They regulate carbohydrate metabolism by stimulating glycogenolysis and gluconeogenesis.
$3$. They influence fat metabolism by promoting lipolysis.
Therefore,thyroid hormones have a regulatory effect on protein,carbohydrate,and fat metabolism.
Hence,the correct option is $D$.

(B) Goiter is an abnormal enlargement of the thyroid gland. It is primarily caused by a deficiency of iodine in the diet,which is essential for the synthesis of the thyroid hormone $Thyroxine$ $(T_4)$. When iodine levels are low,the thyroid gland cannot produce enough $Thyroxine$,leading to a compensatory enlargement of the gland due to increased stimulation by $TSH$ (Thyroid Stimulating Hormone).

(B) The $Thyroid$ gland is unique because it stores its synthesized hormones (thyroxine and triiodothyronine) in the form of thyroglobulin within the colloid of the thyroid follicles. These follicles represent the intercellular spaces where the hormone is stored before being released into the bloodstream upon stimulation by $TSH$ (Thyroid Stimulating Hormone).

(C) The thyroid gland secretes a protein hormone called $Thyrocalcitonin$ $(TCT)$.
$TCT$ plays a crucial role in regulating blood calcium levels.
It acts as a hypocalcemic factor,meaning it lowers the concentration of calcium ions $(Ca^{2+})$ in the blood by inhibiting bone resorption and promoting calcium deposition in the bones.
In contrast,$Parathormone$ $(PTH)$ secreted by the parathyroid gland increases blood calcium levels.

(A) Thyroxine synthesis requires iodine. If a toxic substance inhibits the synthesis of thyroxine,the thyroid gland attempts to compensate for the low levels of circulating thyroxine by increasing in size,a condition known as Simple Goiter.
Thyrotoxicosis and Toxic Goiter are conditions of hyperthyroidism (excessive thyroxine).
Dwarfism is typically associated with a deficiency of Growth Hormone $(GH)$ from the anterior pituitary gland.

(B) Hashimoto's thyroiditis (or Hashimoto's disease) is an autoimmune disorder where the immune system produces antibodies that attack the thyroid gland,leading to hypothyroidism.
In contrast,Graves' disease is an autoimmune condition that leads to hyperthyroidism.
Therefore,the correct answer is Hashimoto's disease.

(D) Hormones are chemical messengers that are secreted by endocrine glands directly into the blood to act on target organs.
$Thyroxine$ is a hormone produced by the thyroid gland that regulates metabolism.
Unlike enzymes,which are biological catalysts that speed up chemical reactions without being consumed,hormones act as signaling molecules that regulate physiological processes.
While enzymes are often proteins,hormones can be proteins,peptides,or amino acid derivatives (like $Thyroxine$,which is an iodinated amino acid).
The primary distinction is functional: enzymes catalyze reactions,whereas hormones regulate them by binding to specific receptors.

(A) Metamorphosis in amphibians,such as the transformation of a tadpole into an adult frog,is regulated by thyroid hormones.
Thyroid hormones,specifically thyroxine $(T_4)$ and triiodothyronine $(T_3)$,contain iodine $(I_2)$ as an essential component.
An increase in the concentration of iodine in the water promotes the synthesis of thyroid hormones,which in turn accelerates the rate of metamorphosis.

(D) The thyroid gland is composed of two lobes which are located on either side of the trachea.
These two lobes are interconnected with a thin flap of connective tissue known as the $Isthmus$.

(C) Metamorphosis in tadpoles is regulated by the thyroid hormone,thyroxine.
Thyroxine synthesis requires iodine.
If tadpoles are raised in water that is deficient in iodine,they will not undergo metamorphosis and will remain in the tadpole stage.
Therefore,adding iodine to the water accelerates the process of metamorphosis by enabling the production of thyroxine in the tadpoles.

(A) The thyroid gland requires iodine for the synthesis of thyroid hormones ($T_3$ and $T_4$).
If there is a deficiency of iodine in our diet,it leads to low production of thyroid hormones and enlargement of the thyroid gland,a condition known as goitre.
Therefore,prolonged disturbance or deficiency in thyroid hormone secretion often manifests as goitre.

(C) The $Thyroid$ gland is the primary site for the storage and utilization of iodine in the human body.
Iodine is an essential component of the thyroid hormones, $Thyroxine$ $(T_4)$ and $Triiodothyronine$ $(T_3)$.
These hormones are synthesized within the thyroid follicles, which actively concentrate iodine from the blood.
Therefore, the thyroid gland contains the highest concentration of iodine compared to any other tissue in the body.

(D) Goiter is an enlargement of the $Thyroid$ gland. It is primarily caused by a deficiency of $Iodine$ in the diet,which is essential for the synthesis of thyroid hormones ($T_3$ and $T_4$). When $Iodine$ levels are low,the $Thyroid$ gland enlarges in an attempt to produce more hormones,leading to the condition known as goiter. Therefore,it is associated with the abnormal functioning of the $Thyroid$ gland.

(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,control the metabolism of carbohydrates,proteins,and fats,and maintain water and electrolyte balance.
Therefore,the primary function is the regulation of the basal metabolic rate.

(B) Metamorphosis in amphibians,such as the transformation of a tadpole into an adult frog,is regulated by the hormone $Thyroxine$.
This hormone is produced by the thyroid gland.
In the presence of iodine,the thyroid gland synthesizes $Thyroxine$,which triggers the physiological and morphological changes required for the tadpole to develop into an adult frog.
Therefore,the correct option is $B$.

(C) $Thyroxine$ is a hormone secreted by the thyroid gland that plays a crucial role in regulating the basal metabolic rate $(BMR)$.
It stimulates the consumption of oxygen and the production of heat in body tissues.
Therefore,an increase in $Thyroxine$ levels leads to an increase in the metabolic rate of the body.

(B) The Basal Metabolic Rate $(BMR)$ of the body is primarily regulated by thyroid hormones,specifically thyroxine $(T_4)$ and triiodothyronine $(T_3)$.
These hormones increase the rate of cellular respiration and oxygen consumption in most body tissues,thereby increasing the metabolic rate.
Therefore,the thyroid gland plays a crucial role in maintaining the $BMR$.

(D) The metamorphosis of a tadpole into an adult frog is regulated by the thyroid hormone (thyroxine).
Thyroxine is essential for the developmental changes that occur during metamorphosis.
If the thyroid gland is surgically removed from a tadpole,the production of thyroxine stops.
Without thyroxine,the tadpole cannot undergo metamorphosis and will continue to grow in size as a tadpole,eventually dying without ever becoming an adult frog.

(A) The $Thyroid$ gland is unique because it stores its hormones (thyroxine and triiodothyronine) in the form of thyroglobulin within the thyroid follicles before releasing them into the bloodstream. Other endocrine glands typically synthesize and release hormones upon stimulation without significant storage.

(A) $Graves'$ disease,also known as exophthalmic goiter,is an autoimmune disorder. It is caused by the overproduction of thyroid hormones ($T_3$ and $T_4$) by the thyroid gland,a condition known as hyperthyroidism. Symptoms include an enlarged thyroid gland (goiter),protrusion of the eyeballs (exophthalmos),increased metabolic rate,and weight loss.

(B) The symptoms described,such as a low metabolic rate,weight gain,and water retention in tissues (edema),are characteristic of $Myxoedema$ in adults. $Myxoedema$ is caused by a deficiency of thyroid hormones $(Thyroxine)$ in adults. While $Hypothyroidism$ is the general condition,$Myxoedema$ is the specific clinical term for the severe form of hypothyroidism in adults.

(C) The hormone $Thyroxine$ $(T_4)$,secreted by the thyroid gland,plays a crucial role in regulating the basal metabolic rate $(BMR)$ of the body.
It stimulates the consumption of oxygen and the production of heat in tissues,thereby increasing the overall metabolic rate.
An injection of $Thyroxine$ will directly elevate the metabolic processes in the body,whereas $STH$ (Somatotropic Hormone) promotes growth,$Insulin$ regulates blood glucose levels,and $Testosterone$ is primarily responsible for male secondary sexual characteristics.

(B) Calcitonin is a peptide hormone secreted by the parafollicular cells ($C$-cells) of the thyroid gland.
It consists of a single polypeptide chain containing $32$ amino acids.
Its primary function is to lower blood calcium levels by inhibiting bone resorption and promoting calcium excretion by the kidneys.

(A) The thyroid gland is the largest endocrine gland in the human body.
It is a butterfly-shaped gland located in the neck,anterior to the trachea.
Although the liver is the largest gland in the body overall,it is classified as an exocrine gland (or mixed gland),not a purely endocrine gland.
Therefore,among the options provided,the thyroid gland is the largest endocrine gland.

(B) The thyroid gland produces two main hormones: Thyroxine $(T_4)$ and Triiodothyronine $(T_3)$.
$T_4$ (Tetraiodothyronine) contains four iodine atoms,while $T_3$ contains three iodine atoms.
Although $T_4$ is produced in larger quantities by the thyroid gland,$T_3$ is the biologically more active form.
Most of the $T_4$ is converted into $T_3$ in the peripheral tissues to exert its physiological effects.
Therefore,$T_3$ is significantly more potent and active than $T_4$.

(D) The thyroid gland produces hormones like thyroxine $(T_4)$ and triiodothyronine $(T_3)$.
Myxedema is a condition resulting from hypothyroidism (under-secretion of thyroid hormones) in adults.
Gigantism,dwarfism,and acromegaly are disorders related to the growth hormone $(GH)$ secreted by the anterior pituitary gland.
Therefore,the correct option is $D$.

(B) Exophthalmic goiter,also known as Graves' disease,is an autoimmune disorder that leads to the hypersecretion of thyroid hormones ($T_3$ and $T_4$).
This condition is characterized by an enlarged thyroid gland,protrusion of the eyeballs (exophthalmos),increased basal metabolic rate,and weight loss.
Therefore,the correct answer is the thyroid gland.

(B) The thyroid gland in amphibians produces the hormone thyroxine,which is essential for the process of metamorphosis. Metamorphosis is the biological process by which a tadpole transforms into an adult frog. If the thyroid gland is removed from a tadpole,the production of thyroxine stops,preventing the tadpole from undergoing metamorphosis. Consequently,the tadpole will continue to grow in size but will never transform into an adult frog,remaining a tadpole for its entire life.

(A) Thyrocalcitonin $(TCT)$ is a protein hormone secreted by the thyroid gland.
Its primary function is to regulate blood calcium levels.
Specifically,$TCT$ acts as a hypocalcemic factor,meaning it lowers the concentration of calcium ions in the blood by inhibiting bone resorption (the breakdown of bone tissue) and promoting the deposition of calcium into the bones.

(A) Hashimoto's disease is an autoimmune disorder where the immune system attacks the thyroid gland.
This leads to the destruction of thyroid tissue,resulting in a decreased production of thyroid hormones ($T_3$ and $T_4$).
Since the thyroid gland is unable to produce sufficient hormones,the condition manifests as hypothyroidism.
Therefore,the symptoms of Hashimoto's disease are similar to those caused by the hyposecretion of thyroxine.

(C) Iodine is a trace element that is essential for the synthesis of thyroid hormones,specifically thyroxine $(T_4)$ and triiodothyronine $(T_3)$.
These hormones are produced by the thyroid gland and play a crucial role in regulating metabolism,growth,and development.
Therefore,iodine is a structural component of these hormones.

(B) : Exophthalmic goitre or Graves' disease is a thyroid enlargement (goitre) in which the thyroid gland secretes an excessive amount of thyroid hormones.
It is characterized by exophthalmia (protrusion of eyeballs due to fluid accumulation behind them),weight loss,a slight rise in body temperature,excitability,rapid heartbeat,nervousness,and restlessness.

(C) The correct answer is $C$. Iodine is essential for the synthesis of thyroid hormones $T_3$ and $T_4$.
Iodine binds to tyrosine residues in thyroglobulin,which is then processed to form triiodothyronine $(T_3)$ and thyroxine $(T_4)$.
If a pregnant female has a deficiency of iodine in her diet,it leads to improper synthesis of thyroid hormones in the developing fetus.
The deficiency of thyroid hormones in infants results in a condition known as 'cretinism'.
The symptoms of cretinism include stunted growth,mental retardation,low intelligence quotient,abnormal skin,and deaf-mutism.

(A) : Iodine is essential for the synthesis of thyroxine. $A$ deficiency of iodine in the diet leads to low production of thyroxine (hypothyroidism) and enlargement of the thyroid gland,a condition known as goitre.
$B$: Corpus luteum secretes progesterone,not testosterone. Progesterone is essential for maintaining the endometrium.
$C$: Oxytocin is synthesized by the hypothalamus and stored/released by the posterior pituitary,not the anterior pituitary.
$D$: Growth hormone $(GH)$ is secreted by the anterior pituitary,not the posterior pituitary.

(C) Iodine is essential for the synthesis of the hormone thyroxine. When toxic agents in food interfere with the uptake of iodine or the synthesis of thyroxine,the thyroid gland is unable to produce sufficient amounts of the hormone. This leads to a decrease in thyroxine levels in the blood. In response to this deficiency,the anterior pituitary gland secretes more thyroid-stimulating hormone $(TSH)$,which causes the thyroid gland to enlarge in an attempt to compensate for the lack of hormone production. This enlargement of the thyroid gland is known as simple goitre or endemic goitre. Therefore,the correct option is $C$.

(B) $(B) :$ Myxoedema is caused by the deficiency of thyroid hormone or thyroxine in adults.
It is characterized by a low metabolic rate,weight gain,puffy appearance,and low body temperature.
This condition can be treated by the administration of thyroid hormones.

(D) Thyroid hormones,specifically $T_3$ (triiodothyronine) and $T_4$ (thyroxine),play a crucial role in erythropoiesis,which is the process of red blood cell formation.
They stimulate the production of erythropoietin by the kidneys,which in turn promotes the maturation and proliferation of red blood cells in the bone marrow.
Therefore,thyroid hormones are essential for maintaining normal hematopoiesis.

(D) The thyroid gland is composed of two lobes which are located on either side of the trachea. Thus,the statement that the thyroid consists of four lobes is incorrect. The thyroid gland is composed of follicles and stromal tissues. Each thyroid follicle is composed of follicular cells enclosing a cavity. These cells synthesize two hormones,tetraiodothyronine or thyroxine $(T_4)$ and triiodothyronine $(T_3)$.

(C) The synthesis of thyroxine $(T_4)$ requires iodine. Certain toxic agents present in food,such as goitrogens (found in vegetables like cabbage and cauliflower),interfere with the uptake of iodine by the thyroid gland or inhibit the synthesis of thyroid hormones. When thyroxine synthesis is inhibited,the thyroid gland enlarges in an attempt to compensate for the low levels of circulating thyroid hormones,a condition known as simple goitre (or endemic goitre). Therefore,the correct answer is $C$.

(A) Grave's disease is an autoimmune disorder that leads to hyperthyroidism,which is the overproduction of thyroid hormones by the thyroid gland.
It is characterized by an enlarged thyroid gland (goiter),protrusion of the eyeballs (exophthalmos),increased metabolic rate,and weight loss.
Therefore,it is directly related to the thyroid gland.

(D) Thyroid hormones ($T_3$ and $T_4$) play a significant role in the regulation of basal metabolic rate and also support the process of erythropoiesis,which is the formation of red blood cells $(RBCs)$.
They stimulate the production of erythropoietin,a hormone produced by the kidneys that triggers the bone marrow to produce more $RBCs$.
Therefore,thyroid hormone is essential for the normal formation and maturation of red blood cells.

(B) Goitre is an enlargement of the thyroid gland.
Thyroid hormones,specifically $T_3$ (triiodothyronine) and $T_4$ (thyroxine),require iodine for their synthesis.
When there is a deficiency of iodine in the diet,the thyroid gland cannot produce sufficient amounts of these hormones.
This leads to a decrease in the negative feedback on the pituitary gland,causing it to release more $TSH$ (thyroid-stimulating hormone).
Continuous stimulation by $TSH$ causes the thyroid gland to enlarge,a condition known as goitre.

(C) is correct: The thyroid gland secretes a peptide hormone known as thyrocalcitonin $(TCT)$,which plays a significant role in regulating blood calcium levels.
$R$ is incorrect: $TCT$ is a hypocalcemic hormone,not a hypercalcemic one. It lowers the blood calcium level by inhibiting the resorption of calcium from bones. $A$ hypercalcemic hormone,such as Parathyroid Hormone $(PTH)$,increases blood calcium levels.

(B) The hormone $Thyroxine$ is essential for the metamorphosis of tadpoles into adult frogs. The presence of iodine in the water is crucial because it is a key component required for the synthesis of $Thyroxine$ by the thyroid gland. If iodine or $Thyroxine$ is added to the water,it accelerates the process of metamorphosis,causing the tadpoles to transform into adult frogs more rapidly.