Thyroid hormones is a result to the release of thyroid stimulating hormones by the pituitary gland. The thyroid, a butterfly shaped gland found in the lower part of the neck produces two types of tyrosine based hormones. These are thyroxine (T4) and triiodothyronine (T3). T4 and T3 ratio that is released to the blood is approximately around 20 to 1. Thyroid hormones are the only major biochemical molecules that incorporates iodine which is present in all chordate animals. Iodine is the key component in the synthesis of thyroid hormones, and the lack can lead to the thyroid condition hypothyroidism. 

The role of thyroid hormones in the body is to help in the conversion of food into energy and heat. Triiodothyronine or T3 is directly responsible and pushes metabolism in mitochondria. Triiodothyronine is the catalyst for faster protein synthesis, reading of genes, and mitochondrial gene transcription. All this action causes an increase in free fatty acids as well as breakdown of proteins. And to meet the increased oxygen need of the body to do all those things, thyroid hormones elevates our heart rate.

Thyroid hormones are the ones responsible for controlling our body temperature. In order to keep our core temperature at a safe level, our thyroid hormones fluctuate depending on the caloric intake and external temperature. During the absence of food, the production of thyroid hormones is lowered to stop the building up of ketone bodies in our blood and kidneys. And also to ease caloric demand. If the body doesnt do this, ketone buildup can damage the sensitive kidneys and other parts of our body.

Thyroid stimulating hormones or TSH is the only hormone that thyroid hormones are not sensitive to. The hormone estrogen prevents the effectiveness of thyroid hormones. Thats the reason why women have a much larger thyroid gland compared to men, and are also more prone to thyroid diseases. As for growth hormones, they do hinder thyroid hormones but also compliments it with regards to metabolism, development, and growth.

The role thyroid hormones play in metamorphosis and development in all vertebrates is a major one. By binding itself to thyroid hormone receptors which are molecules that changes their shape to an activated one, it affects development. As for gene transcription to happen, the thyroid hormone activates the thyroid hormone receptors and tells it to bind with responsive elements in the DNA. The copying and blocking of some genes is facilitated by the attaching of thyroid hormones to responsive elements. 

Experts are still studying other genes that might be influenced by the presences of thyroid hormones. But from the findings that they already have gathered, it only shows how important thyroid hormones are to us.