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 hypothyroidism.

And you can find written notes on this topic at zero tofinals.com slash hypothyroidism or in the endocrinology section of the zero to finals medicine book.

So let's get straight into it.

Hypothyroidism refers to insufficient thyroid hormones, specifically tri-iodothyronine, which is

T3 and thyroxine, which is T4.

Primary hypothyroidism is where the thyroid gland behaves abnormally and produces inadequate

thyroid hormones. Due to the lack of thyroid hormones, negative feedback is absent, and this results in

increased production of thyroid stimulating hormone by the pituitary gland. The pituitary is trying

extra hard to get a response out of the thyroid. Therefore, in primary hypothyroidism, thyroid

thyroid stimulating hormone is raised and and T-3 and T-4 are low.

Secondary hypothyroidism, also called central hypothyroidism, is where the pituitary gland behaves

abnormally and produces inadequate thyroid stimulating hormone, resulting in

understimulation of the thyroid gland and insufficient thyroid hormones. In secondary

hypothyroidism, thyroid stimulating hormone T3 and T4 will all be low.

As a summary in primary hypothyroidism, the problem is in the thyroid gland, Tsh will be high

and T3 and T4 will be low.

In secondary hypothyroidism, the problem is in the pituitary gland.

TSH will be low and T-3 and T-4 will also be low.

Let's talk about the causes of primary hypothyroidism.

Hashimoto's thyroiditis is the most common cause of hypothyroidism in the developed world. It's an autoimmune

condition causing inflammation of the thyroid gland. It's associated with antithyroid peroxidase or

anti-tipo antibodies and antithyroglobulin or anti-TG antibodies.

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