The central lumens of thyroid follicles are filled with colloid, which consists of the protein a molecule that binds and stores thyroid hormone.

The central lumens of thyroid follicles are filled with colloid, which consists of the protein thyroglobulin, a molecule that binds and stores thyroid hormone.

Thyroglobulin is a protein produced primarily by the thryroid gland. The thyroid gland is mainly made up of tiny, round shaped structures called follicles that produce and store thyroglobulin. Thyroglobulin acts as a substrate for the synthesis of the hormones (thyroxine and triiodothyronine) and also the storage of the inactive forms of thyroid hormone and iodine. Thyroxine and triiodothyronine assist in the regulation of the utilization of energy by the body.

answer: accepted answer: aquatic animals use the oxygen dissolved in water to carry out respiration. since the amount of dissolved oxygen in water is low as compared to the amount of oxygen in the air, therefore the rate of breathing in aquatic animals is much faster than it is in terrestrial animals.

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