# The Endocrine System - Author: **Susanne Hiller-Sturmhöfel** - Document Tags: [[hormone]] - [URL link](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6761896/)  ## Highlights - The gland produces two structurally related hormones, thyroxine (T4) and triiodothyronine (T3), that are iodinated derivatives of the amino acid tyrosine. ([View Highlight](https://read.readwise.io/read/01hmppkkcvvapn88wh62q3tw5x)) (Tags: [[thyroid]], [[triiodothyronine t3]], [[tyrosine]], [[amino acids]], [[thyroxine t4]], [[thyroxine]]) --- - T4 constitutes approximately 90 percent of the hormone produced in the thyroid gland. ([View Highlight](https://read.readwise.io/read/01hmpq8efqz8xqp02qpttgpc58)) (Tags: [[thyroid]], [[thyroxine t4]], [[thyroxine]]) --- - However, T3 is a much more active hormone, and most of the T4 produced by the thyroid is converted into T3 in the liver and kidneys. ([View Highlight](https://read.readwise.io/read/01hmpq968dfh8qz0j38mnrz8w6)) ---