The correct option is (b).
Explanation
Goitre is a pathological condition characterized by the enlargement of the thyroid gland, which is located in the neck region. It is primarily an endocrine disorder related to the regulation of thyroid hormones.
Detailed Analysis:
- Thyroid Function and Thyroxine: The thyroid gland requires iodine to synthesize the hormone thyroxine (T4). Thyroxine plays a crucial role in regulating the body's basal metabolic rate (BMR).
- Mechanism of Goitre: When there is a deficiency of iodine in the diet, the thyroid gland is unable to produce sufficient quantities of thyroxine. In response to low levels of thyroxine in the blood, the anterior pituitary gland secretes excess Thyroid Stimulating Hormone (TSH). This continuous stimulation causes the thyroid gland to enlarge in an attempt to trap more iodine from the blood, resulting in the swelling known as Goitre.
- Analysis of Other Options:
- (a) Lack of insulin: Insulin deficiency leads to Diabetes Mellitus, characterized by high blood sugar levels, not Goitre.
- (c) Excess secretion of adrenalin: Adrenalin (epinephrine) is the "fight or flight" hormone. Its excess secretion causes increased heart rate and blood pressure but does not cause thyroid enlargement.
- (d) Viral infection: While some forms of thyroiditis can be viral, the classic Goitre described in general physiology is a deficiency or metabolic disorder, not a water-borne viral disease.
Key Takeaway:
Goitre is caused by the enlargement of the thyroid gland due to its inability to produce sufficient thyroxine, often resulting from a dietary deficiency of iodine.