Question

Which hormone controls growth, mental faculties and tissue differentiation ?
A) Glucagon
B) Parathormone
C) Thyroxine
D) Cortisone

Answer 1

The thyroid gland secretes three hormones. Thyroxine (tetraiodothyronine or t4) and triiodothyronine or t3 are secreted by the thyroid follicular cells. The thyroid gland is the only gland that stores its hormones in large quantities. T4 and t3 are synthesised by attaching iodine to tyrosine amino acid.

Complete answer:
The hormone that controls growth, mental faculties and tissue differentiation is Thyroxine hormone. Functions of thyroxine hormone are :
i) They regulate the metabolic rate of the body and thus maintain basal metabolic rate (BMR)
ii) They stimulate protein synthesis and therefore promote growth of the body tissues.
iii) They regulate the development of mental faculties.
iv) As they increase heat production, thus they maintain body temperature.
v) They help in metamorphosis of tadpoles into adult frogs, if the thyroid gland of the tadpole(larvae) is removed, the larva fails to change into an adult.
vi) They increase the action of neurotransmitters like adrenaline and noradrenaline.

Also, Thyrocalcitonin (TCT) is secreted when calcium level is high in the blood. It then lowers the calcium level by suppressing release of calcium ions from the bones. Thus thyrocalcitonin has an action opposite to that of the parathyroid hormone on calcium metabolism. Thyrocalcitonin is also called calcitonin. It is a peptide which contains 32 amino acids.

Thus the correct answer is option (C) Thyroxine

Note: More or less secretion of thyroxine hormone causes thyroid disorders.
i) Hyperthyroidism: includes exophthalmic goitre / grave’s disease/ parry’s disease. It is an enlargement of the thyroid which secretes excessive amounts of thyroxine hormone.
ii) Hypothyroidism: caused by deficiency of thyroid hormone. It includes : cretinism, myxoedema, simple goitre and hashimoto disease.