Hello and welcome to the Zero to Finals podcast.

My name is Tom and in this episode I'm going to be talking to you about thyroid hormones.

And you can find written notes on this topic at zero to finals.com slash thyroid hormones or in the endocrinology

section of the second edition of the zero to finals medicine book. And you can find digital

flashcards and questions to train your knowledge on this content and help you remember it

for longer at members.0.0.5.com.

So let's get straight into it.

The thyroid gland sits at the front of the neck and produces the two thyroid hormones,

which are triiodothyronine, or T3, and thyroxine, or T4.

T4 breaks down into T3 in the tissues, and T3 is the more active thyroid hormone, meaning it has a

greater effect on the body tissues. T4 has a longer

half-life of around seven days compared with the half-life of T3, which is around one day. The longer

half-life of T-4 helps to keep the thyroid hormone levels more stable over time.

Let's talk about thyroid hormone production.

Inside the thyroid gland, there are structures called follicles. These structures aligned by follicular

cells and contain a fluid called colloid.

The follicular cells produce thyroid hormones.

Iodine is an essential component in the production of thyroid hormones.

Iodine enters the follicular cells and the colloid as iodide, or I-minus.

Thyroid peroxidase is an essential enzyme in the colloid that oxidizes iodide, or I-minus, to iodine, or i-plus. The colloid contains an important protein called

thyroglobulin. Thyroglobulin, which is produced by the follicular cells, acts as a scaffolding

structure for the production of thyroid hormones.

...