Thyroid Gland Questions in English

(A) Metamorphosis in frogs is the process of transformation from a tadpole to an adult frog.
This process is regulated by the thyroid hormone,thyroxine.
Thyroxine synthesis requires iodine as a key component.
Therefore,the presence of iodine in the water is essential for the production of thyroxine,which in turn promotes and accelerates the metamorphosis of the tadpole into an adult frog.

(C) Iodine is an essential trace element required for the synthesis of thyroid hormones,specifically $T_3$ (triiodothyronine) and $T_4$ (thyroxine).
These hormones play a critical role in regulating the basal metabolic rate $(BMR)$ and the general metabolism of the body.
$A$ deficiency of iodine leads to a decrease in the production of these hormones,resulting in hypothyroidism,which significantly impacts the body's metabolic processes.

(D) Iodine is an essential trace element required for the synthesis of thyroid hormones ($T_3$ and $T_4$).
Deficiency of iodine in the diet leads to the enlargement of the thyroid gland,a condition known as $Goitre$.
$Kwashiorkor$ and $Marasmus$ are caused by protein-energy malnutrition,while $Anaemia$ is typically caused by iron deficiency.

(B) Thyroxine $(T_4)$ and growth hormone $(GH)$ act synergistically to promote growth and development in the body.
Thyroxine is essential for the normal secretion and action of growth hormone.
Therefore,the activity of growth hormone increases in the presence of thyroxine,as thyroxine stimulates protein synthesis and metabolic processes that support the effects of $GH$.

(D) Calcitonin is a peptide hormone that plays a crucial role in calcium homeostasis by lowering blood calcium levels.
It is secreted by the parafollicular cells,also known as $C$-cells,which are located within the thyroid gland.

(A) Simple goitre is caused by a lower intake of iodine through the diet.
Goitre is the swelling of the neck due to the enlargement of the thyroid gland.
Iodine is essential for the synthesis of thyroid hormones ($T_3$ and $T_4$).
Deficiency leads to hypothyroidism,resulting in the compensatory enlargement of the thyroid gland.

(C) is the correct answer. Myxoedema occurs due to the deficiency of thyroxine in adults.
The peculiar feature of myxoedema is that the face and hands become swollen due to the deposition of albuminous myxomatous tissue.

(D) Cretinism is caused by the hyposecretion of thyroid hormones (thyroxine) during childhood or from birth.
This condition is known as childhood hypothyroidism.
The primary symptoms include stunted physical growth (dwarfism) and mental retardation.

(B) . Exophthalmic goitre $(Grave's\,disease)$ is a form of hyperthyroidism.
It occurs due to the overproduction of thyroid hormones,which leads to an abnormally high metabolic rate.
Clinical features include the protrusion of the eyeballs due to the accumulation of fluid and connective tissue in the eye orbits.

(B) The correct answer is $B$. Thyroxin is the hormone secreted by the thyroid gland. It plays a critical role in the metamorphosis of a frog's tadpole into an adult frog. Without sufficient levels of thyroxin,the tadpole cannot undergo metamorphosis.

(D) Thyroxin was first isolated in crystalline form by Edward Calvin Kendall in $1914$.
None of the given options ($A$,$B$,$C$) are correct.
Therefore,the correct answer is $D$.

(B) The symptoms described,such as being fat,short,and stocky with a dull appearance (stupid look) and a protruding tongue,are characteristic of $Cretinism$.
$Cretinism$ is a condition caused by the deficiency of thyroid hormones ($T_3$ and $T_4$) during fetal development or early childhood (congenital hypothyroidism).
These hormones are essential for normal physical growth and mental development.
Therefore,the correct answer is $Thyroid$.

(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 as an essential component.
Therefore,the presence of iodine $(I_2)$ is crucial for the synthesis of these hormones.
If iodine is added to the water in which tadpoles are developing,it accelerates the production of thyroid hormones,thereby speeding up the process of metamorphosis.

(A) The thyroid gland is sensitive to the levels of thyroid hormones ($T_3$ and $T_4$) in the blood.
When there is an excess of thyroid hormone secretion (hyperthyroidism),the gland often enlarges due to overactivity or autoimmune conditions like Graves' disease.
Conversely,when there is a deficiency of thyroid hormone secretion (hypothyroidism),the pituitary gland increases the secretion of Thyroid Stimulating Hormone $(TSH)$.
This constant stimulation by $TSH$ causes the thyroid gland to grow in size in an attempt to produce more hormone,a condition known as a goiter.
Therefore,in both cases of hyperthyroidism and hypothyroidism,the gland typically becomes enlarged.

(B) 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 stimulate the cellular respiration process,which increases the consumption of oxygen and the production of energy $(ATP)$ in body cells.
Therefore,the energy-releasing process in body cells is initiated and regulated by the thyroid gland.

(C) An endocrine disorder occurs when there is an imbalance in hormone levels or a malfunction of the endocrine glands.
$A$. Pneumonia is a respiratory infection caused by bacteria,viruses,or fungi.
$B$. Typhoid is a bacterial infection caused by $Salmonella$ $typhi$.
$C$. Goitre is an enlargement of the thyroid gland,which is an endocrine gland. It is typically caused by a deficiency of iodine,which is required for the synthesis of thyroid hormones ($T_3$ and $T_4$). Thus,it is classified as an endocrine disorder.
$D$. Jaundice is a condition caused by high levels of bilirubin,often related to liver dysfunction.
Therefore,the correct option is $C$.

(C) Hypothyroidism is a condition caused by the deficiency of thyroid hormones.
Key features include a decrease in the metabolic rate,weight gain,and lethargy.
In severe cases,such as myxedema,there is an accumulation of mucus-like substances,specifically albumin protein and polysaccharides,in the subcutaneous tissue (below the skin),leading to puffiness.
Weight loss,increased metabolic rate,and irritability are characteristic of hyperthyroidism,not hypothyroidism.

(D) Antithyroid substances are compounds that interfere with the synthesis,release,or action of thyroid hormones.
$1$. Thiocyanate ions inhibit the uptake of iodide by the thyroid gland.
$2$. Propylthiouracil inhibits the enzyme thyroid peroxidase,which is essential for the iodination of tyrosine residues in thyroglobulin.
$3$. High concentrations of inorganic iodides (Wolff-Chaikoff effect) can temporarily inhibit the synthesis and release of thyroid hormones.
Therefore,all the listed substances are considered antithyroid substances.

(D) The correct answer is $(d)$.
Goitre is the enlargement of the thyroid gland,which is primarily caused by a deficiency of iodine.
Iodine is a trace element found in the soil and water of coastal regions,but it is often leached out of the soil in mountainous regions due to erosion and snowmelt.
Consequently,both the water and the crops grown in these regions are deficient in iodine.
Since iodine is essential for the synthesis of thyroid hormones ($T_3$ and $T_4$),its deficiency leads to the compensatory enlargement of the thyroid gland,a condition known as goitre.

(D) The $Thyroid$ gland is composed of tiny follicles,which are hollow spheres whose walls consist of a single layer of cuboidal epithelium.
In these follicles,thyroid hormones are stored in the extracellular space,bound to a protein called thyroglobulin,which is synthesized by the follicular cells.
To release the hormones into the blood,the epithelial cells take up thyroglobulin via pinocytosis and subsequently remove the active hormone from the thyroglobulin molecule.

(D) The $BMR$ (Basal Metabolic Rate) is primarily regulated by the hormone thyroxine $(T_4)$ and triiodothyronine $(T_3)$.
These hormones are secreted by the thyroid gland.
Thyroxine increases the rate of cellular respiration and oxygen consumption,thereby increasing the $BMR$ of the body.

(B) The correct answer is $B$. The thyroid gland is the primary site in the body that actively absorbs and concentrates iodine from the blood to synthesize thyroid hormones ($T_3$ and $T_4$).
The thyroid gland acts as a reservoir for iodine.
It utilizes approximately $150 \, \mu g$ $(0.15 \, mg)$ of iodine daily for hormone production.
Therefore, an individual must consume at least $150 \, \mu g$ of iodine daily through their diet to maintain normal thyroid function.

(C) The thyroid gland is a highly vascularized endocrine organ located in the neck. It produces thyroid hormones ($T_3$ and $T_4$). $A$ deficiency of thyroid hormones during fetal development or early childhood leads to a condition characterized by stunted physical growth and mental retardation,known as cretinism.

(A) $Thyroxine$ is an iodine-containing amine hormone that is derived from the amino acid $Tyrosine$ and is secreted by the $Thyroid$ gland.

(A) $Cretinism$ is a condition caused by the deficiency of thyroid hormones ($T_3$ and $T_4$) during fetal development or infancy,leading to stunted growth and mental retardation.
$Myxoedema$ is caused by the deficiency of thyroid hormones in adults.
$Graves'$ disease or $exophthalmic$ $goitre$ is caused by the hypersecretion of thyroid hormones.
Therefore,the correct option is $A$.

(A) The correct answer is $A$.
Iodine is an essential mineral required for the synthesis of thyroid hormones,specifically thyroxine $(T_4)$ and triiodothyronine $(T_3)$.
An adult human body contains about $5$ to $6 \text{ mg}$ of iodine,and the majority of this iodine is concentrated in the thyroid gland to facilitate hormone production.
Deficiency of iodine leads to the enlargement of the thyroid gland,a condition known as goiter.

(B) . The most important function of thyroid hormones ($T_3$ and $T_4$) is to regulate the basal metabolic rate $(BMR)$ in our body.
These hormones are secreted by the thyroid gland,which stimulates the consumption of oxygen and the production of $ATP$,thereby increasing the body's metabolic activity and heat production.

(A) Iodine is an essential trace element required for the synthesis of thyroid hormones,specifically Thyroxin $(T_4)$ and Triiodothyronine $(T_3)$.
Thyroid follicles produce these hormones by incorporating iodine atoms into the amino acid tyrosine.
Deficiency of iodine leads to the enlargement of the thyroid gland,a condition known as goiter.

(D) . The $Thyroid$ gland plays a key role in the metamorphosis of a frog's tadpole. The $Thyroid$ hormones, specifically $Thyroxine$, initiate and regulate the process of metamorphosis. Metamorphosis is the biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation, transforming the larva into an adult.

(A) Goitre is an enlargement of the thyroid gland caused by a deficiency of iodine in the diet.
Iodine is essential for the synthesis of thyroid hormones ($T_3$ and $T_4$).
These hormones play a critical role in regulating the basal metabolic rate $(BMR)$,protein synthesis,and carbohydrate and fat metabolism.
Therefore,goitre primarily affects the body's metabolism.

(D) Thyroxine is classified as a hormone because it is a chemical messenger produced by an endocrine gland (the thyroid gland) and is secreted directly into the bloodstream to regulate physiological processes in target organs. Unlike enzymes,which are biological catalysts that speed up chemical reactions without being consumed,hormones act as signaling molecules that alter the activity of target cells. The defining characteristic of an endocrine hormone is its ductless secretion directly into the blood.

(C) Autoimmune thyroiditis is a condition where the immune system attacks the thyroid gland. This condition is clinically known as $Hashimoto's$ disease.
In this disorder,the body produces antibodies that damage thyroid cells,leading to hypothyroidism.
$Addison's$ disease involves adrenal insufficiency,$Simmond's$ disease refers to panhypopituitarism,and $Cushing's$ disease is caused by excess cortisol production.

(A) The correct answer is $A$. Goitre is a condition characterized by the enlargement of the thyroid gland. It occurs when the thyroid gland fails to produce sufficient thyroxine hormone,often due to iodine deficiency. In an attempt to compensate for the low hormone levels,the gland increases in size,leading to the condition known as goitre.

(D) Calcitonin is a peptide hormone secreted by the parafollicular cells ($C$-cells) of the thyroid gland.
Its primary function is to lower blood calcium levels when they become too high.
Therefore,when blood calcium levels rise above the normal range,a condition known as $Hypercalcemia$,the thyroid gland is stimulated to secrete calcitonin.
Calcitonin acts by inhibiting osteoclast activity in bones and increasing calcium excretion by the kidneys,thereby restoring calcium homeostasis.

(A) Iodine is an essential trace element required for the synthesis of thyroid hormones,specifically thyroxine $(T_4)$ and triiodothyronine $(T_3)$.
When iodine is ingested,it is absorbed into the bloodstream and selectively taken up by the thyroid gland.
The thyroid gland uses this iodine to produce its hormones,which regulate the body's metabolic rate.
Therefore,the thyroid gland is the primary site for the storage and utilization of iodine in the human body.

$(D)$ is the correct answer.
Hashimoto's thyroiditis is an autoimmune disorder where the immune system attacks the thyroid gland, leading to its gradual destruction. Because the body's own immune system causes the destruction of the gland, it is often referred to as the "suicide of the thyroid" or the "suicide gland".

(A) The condition described is known as cretinism,which occurs due to hypothyroidism during fetal development or early childhood.
Thyroxine is essential for the normal development and differentiation of the central nervous system and brain.
$A$ deficiency of thyroxine leads to stunted physical growth and mental retardation,resulting in a low $I.Q.$ equivalent to that of a young child.

(B) Thyroxine is a hormone secreted by the thyroid gland.
It plays a crucial role in regulating the body's metabolic rate,growth,and development.
It is an iodine-containing amino acid derivative.

(D) The thyroid gland in amphibians secretes hormones (thyroxine) that are essential for the process of metamorphosis,which is the transformation of a tadpole into an adult frog.
If the thyroid gland is completely removed,the tadpole will lack the necessary hormonal stimulus to undergo metamorphosis.
Consequently,it will fail to develop into an adult frog and will remain in the tadpole stage throughout its life.

(B) Metamorphosis in amphibians,such as the transformation of a tadpole into an adult frog,is primarily regulated by the thyroid gland.
Thyroxine is the specific hormone secreted by the thyroid gland that triggers the physiological and morphological changes required for this process.
Without sufficient levels of thyroxine,the tadpole cannot complete its development into an adult frog.

(A) The endoderm is the innermost germ layer formed during gastrulation.
It gives rise to the epithelial lining of the gastrointestinal tract,the respiratory system,and several glands.
The thyroid gland is derived from the endoderm of the pharyngeal floor.
The pineal gland and pituitary gland are derivatives of the ectoderm (neuroectoderm),while the spleen is derived from the mesoderm.

(C) Genetic diseases are caused by abnormalities in an individual's genome,such as mutations in a single gene or chromosomal aberrations.
$A$. Haemophilia is an $X$-linked recessive genetic disorder.
$B$. Daltonism (color blindness) is an $X$-linked recessive genetic disorder.
$C$. Myxoedema is a condition resulting from severe hypothyroidism (deficiency of thyroid hormones),which is typically caused by iodine deficiency or autoimmune issues,not by a genetic mutation.
$D$. Alkaptonuria is an autosomal recessive metabolic genetic disorder.
Therefore,Myxoedema is not a genetic disease.

(C) Hashimoto's thyroiditis is an autoimmune disorder in which the immune system attacks the thyroid gland.
Over time,this leads to the destruction of thyroid tissue,which is why it is often referred to as 'thyroid's suicide'.
It results in hypothyroidism,where the gland cannot produce enough thyroid hormones.

(D) Grave's disease,also known as exophthalmic goiter,is an autoimmune disorder caused by the hypersecretion of thyroid hormones ($T_3$ and $T_4$).
Key symptoms include:
$1$. Enlargement of the thyroid gland (goiter).
$2$. Increased Basal Metabolic Rate $(BMR)$,leading to weight loss and heat intolerance.
$3$. Increased nervous activity,causing tremors and anxiety.
$4$. Exophthalmia (protrusion of the eyeballs due to swelling of the tissues behind the eyes).
Therefore,all the given options are associated with Grave's disease.

(D) Myxoedema is a condition caused by hypothyroidism in adults,which is a deficiency of thyroid hormones ($T_3$ and $T_4$).
Symptoms of myxoedema include a swollen face (puffy appearance),mental dullness,dry and coarse skin,weight gain,and loss of appetite.
Goitre is the enlargement of the thyroid gland.
Acromegaly is caused by the excess secretion of growth hormone in adults.
Tetany is caused by low levels of calcium in the blood due to hypoparathyroidism.

(D) Hormones are classified based on their chemical structure into peptide,steroid,and amino acid derivatives.
$1$. Insulin,Oxytocin,and Erythropoietin are peptide hormones,which are chains of amino acids.
$2$. Thyroxine (also known as $T_4$) is a derivative of the amino acid tyrosine.
Therefore,Thyroxine is the correct answer.

(A) Goiter is a condition characterized by the enlargement of the thyroid gland.
This condition is primarily caused by a deficiency of iodine in the diet.
Iodine is an essential trace element required for the synthesis of thyroid hormones ($T_3$ and $T_4$).
When iodine levels are low,the thyroid gland enlarges in an attempt to capture more iodine from the blood,leading to the development of a goiter.

(B) The thyroid gland is composed of numerous spherical structures called thyroid follicles.
Each thyroid follicle is lined by a single layer of epithelial cells known as follicular cells.
These follicular cells are cuboidal in shape,hence the epithelium is classified as simple cuboidal epithelium.
This epithelium is responsible for the synthesis and secretion of thyroid hormones ($T_3$ and $T_4$).

(B) Hypothyroidism in adults is caused by a deficiency of thyroid hormones. This condition leads to a disease known as $Myxedema$. Symptoms include swelling of the face and hands,lethargy,and a slow heart rate. $Addison's$ $disease$ is related to adrenal insufficiency,$Infertility$ is a broad term,and $Dwarfism$ in thyroid context is known as $Cretinism$ (in children).

(D) Hypothyroidism in adults is caused by a deficiency of thyroid hormones.
In adults,this condition leads to a disorder known as $Myxedema$.
Symptoms include puffiness of the face and hands,lethargy,and a slow heart rate.
$Dwarfism$ is typically associated with hypothyroidism in children (cretinism),not adults.