How hypothyroidism cause a goitre to develop?

In hypothyroidism, the thyroid gland is unable to produce enough thyroid hormones. This leads to a feedback mechanism in which the pituitary gland senses the low levels of thyroid hormones and responds by releasing more thyroid-stimulating hormone (TSH).

TSH stimulates the thyroid gland to produce more thyroid hormones. However, in hypothyroidism, the thyroid gland is unable to respond adequately to TSH stimulation. This causes the thyroid gland to enlarge in an attempt to meet the body's demand for thyroid hormones. The enlargement of the thyroid gland is referred to as a goitre.

The goitre in hypothyroidism is usually smooth and symmetrical and it may become visible and cause swelling in the neck area. Nodular goiters (with the growth of lumps or nodules within the enlarged thyroid gland) can also occur in some cases of hypothyroidism.