You may have heard of the thyroid, but you don’t know where it is or what it looks like. Here’s a look at this “small, big” gland.
What does the thyroid look like?
What does the thyroid look like?
The “English” name for the thyroid is Thyroid, which is butterfly-shaped or “H” shaped like a shield, hence the name.
The thyroid gland usually weighs about 20-30 grams and is divided into two lateral lobes, connected by an isthmus, and in some people, the isthmus also extends upward to a cone lobe. Each lateral lobe is about 5 * 3 * 2 cm in size, and the isthmus is about 2 cm wide.
The thyroid gland is surrounded by two layers of perithelium, the outer layer called the surgical perithelium of the thyroid gland and the inner layer, the intrinsic perithelium of the thyroid gland, with loose connective tissue between the two layers.
Where is the thyroid gland?
The normal thyroid gland is located 2-3 cm below the thyroid cartilage (the “laryngeal node”) in the anterior middle of the neck, and the isthmus of the thyroid gland is mostly located in the second to fourth tracheal rings.
The normal thyroid gland is palpable but not visible, and is only visible when it is enlarged, which is known as “thick neck disease”. The thyroid gland is anchored to the trachea and cricoid cartilage by the outer tegument, and to the cricoid cartilage by the suspensory ligaments on the medial side of the upper poles of both lobes. This is why the thyroid gland moves up and down as we swallow.
There may be some variation in the shape and location of the thyroid gland, called “ectopic thyroid”. This means that the thyroid gland is not in its normal position in the neck, but appears in other areas where it may pass during embryonic development, such as in the pharynx, tongue, supraglottis, subglottis, anterior larynx, and sternum. This is essentially a disorder of abnormal thyroid development.
Where does the blood supply to the thyroid gland come from?
The thyroid gland has a very rich blood supply, mainly from the superior thyroid artery and the inferior thyroid artery, and in some people, the inferiormost thyroid artery. It is estimated that blood from the whole body passes through the thyroid once every hour. These blood vessels are interconnected, so although the surgeon ligates all the upper and lower thyroid arteries during surgery, it does not usually cause ischemia or necrosis. There is also a rich network of veins within the thyroid gland.
What’s around the thyroid?
Lymph nodes
There are cervical lymph nodes around the thyroid gland. Internationally, they are divided into 7 zones, identified by Roman numerals I to VII. Zones VI to VII are the central zone lymph nodes and zones I to V are the lateral cervical zone lymph nodes.
Once a thyroid cancer metastasizes, the first stop is often in the central zone and then spreads to the lateral cervical zone.
Parathyroid glands
There are generally four parathyroid glands on the back of the two lobes of the thyroid, between the two layers of the peritoneum. The upper two are relatively fixed and the lower two are not. In adults, the parathyroid glands are yellow or tan, long and oval, the size of a green bean to a soybean, and usually encased in fatty tissue.
Returning laryngeal nerve and superior laryngeal nerve
On the back of the thyroid lobes on both sides, the recurrent laryngeal nerve and the superior laryngeal nerve pass through. These two nerves work together to regulate the sensory and motor innervation of the vocal cords, thus regulating speech and respiratory function. They are vulnerable to damage during thyroid disease or surgery.
In addition, the thyroid gland is adjacent to important tissues such as the trachea, esophagus, and common carotid artery. Therefore, when a tumor occurs in the thyroid, it may cause involvement of adjacent tissues.
What are the functions of the thyroid gland?
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Co-written by Dr. Tingting Zhang, Cancer Hospital of Fudan University