Question

Iodine is an important constituent of:
1. Salt
2. Food
3. Thyroxine
4. Hemoglobin

Answer 1

Correct Answer - Option 3 : Thyroxine

The correct answer is Thyroxine.
Concept-
Iodine is an important constituent of Thyroxine because it regulates the synthesis of thyroxine in thyroid glands.

Explanation:
Thyroid gland-

• Thyroid gland is known to be the largest endocrine gland.
• The thyroid gland is bilobed, high vascular organ.
• The thyroid gland is composed of follicles (round in shape) and stromal tissues. 
• Each thyroid follicle is composed of follicular cells, enclosing a cavity. 

Hormones-

• These are non-nutrient chemicals which are responsible for regulating the biological processes in the body.
• These follicular cells synthesize the following two hormones

1. Tetraiodothyronine or thyroxine (T₄) hormone
2. Triiodothyronine (T₃) hormone.

• Both these forms are iodinated forms of the amino acid. 
• Iodine (in diet) 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.
• When rate of synthesis and secretion of thyroid hormones is increased to abnormal high levels then this condition is known as Hyperthyroidism. It adversely affects body physiology of an organism.

Thyroxine hormone has the following functions in humans:

• They maintain the basal metabolic rate of the body.
• They promote growth of body tissues and development of mental faculties.
• They stimulate tissue differentiation.
• Thyroxine also controls the working of kidneys. Its deficiency results in decreased urine output and vice-versa.