Читать книгу The Healthy Thyroid: What you can do to prevent and alleviate thyroid imbalance - Patsy Westcott - Страница 17

The thyroid is a small, soft, butterfly-shaped gland that weighs just 15–20 g (¹/₂–³/₄ oz) and is about the size of a plum, yet it is also the largest pure endocrine gland in the body. It lies across the front of the windpipe (trachea) just below the larynx, or voice box (see Figure 2.3). Its two lobes, or sections, lie on either side of the Adam’s apple and are joined together by a narrow bridge of tissue called the isthmus.

You may just be able to detect its outline if you look in the mirror and stretch your neck. If you take a sip of water and swallow, you may be able to see it moving up and down. If you can’t see it, you may be able to feel it with your fingers. (But don’t worry if you can’t see or feel it – not everyone can.)

The thyroid develops in the womb during the first weeks of life from a small piece of tissue at the root of the tongue. As the fetus grows, the tissue moves down the neck to rest at its adult position. By the time the fetus is just 12 weeks old, the thyroid has already started to work.

The thyroid is made up of two types of hormone-secreting tissue: follicular cells and parafollicular cells. The follicular cells, which make up the greater part of the thyroid, are hollow spheres surrounded by tiny capillary blood vessels, lymphatic vessels and soft connective tissue. Each follicle is filled with a yellow, semifluid, protein-containing material called thyroglobulin (TG) which, when broken down, interacts with

Figure 2.3 The thyroid gland lies across the windpipe in the throat.

iodine stored in the thyroid to produce thyroid hormone (TH). The parafollicular cells lie on their own or in small clusters in the spaces between the follicles and secrete another hormone – calcitonin.