The thyroid gland (glandula thyroidea) is the largest endocrine gland located on the front surface of the neck. Its mass is 20–30 g, and its shape resembles a butterfly. Thyroid hormones regulate the metabolism of every cell of the body.
Building
The gland consists of:
- Right and left lobes - located on the sides of the trachea
- Isthmus - connects the lobes in front of the 2–4 tracheal rings
- Pyramidal lobe - occurs in 30–50% of people, a rudiment of the thyroglossal duct
Microscopically, the gland consists of follicles - spherical vesicles with a diameter of 50–500 microns, filled with colloid (thyroglobulin). Follicular cells (thyrocytes) synthesize thyroid hormones, and parafollicular C-cells synthesize calcitonin.
Hormones
Thyroxine (T4) is the main secretion product (90%), contains 4 iodine atoms. In tissues it turns into more active T3.
Triiodothyronine (T3) - 3-5 times more active than T4, contains 3 iodine atoms. It is T3 that acts on cell receptors.
Effects of thyroid hormones:
- Increase oxygen consumption and heat production
- Stimulate protein synthesis
- Accelerate the breakdown of fats and carbohydrates
- Necessary for brain development in the fetus and child
- Affect heart rate
Calcitonin - reduces calcium levels in the blood by inhibiting the activity of osteoclasts (cells that destroy bone).
Regulation
The synthesis of hormones is controlled by the feedback principle:
- The hypothalamus secretes TRH (thyrotropin-releasing hormone)
- The pituitary gland secretes TSH (thyroid-stimulating hormone)
- TSH stimulates the thyroid gland
- Increased T3/T4 suppresses TSH secretion
Diseases
Hypothyroidism - decreased function: fatigue, edema, weight gain, chilliness, bradycardia. Causes: autoimmune thyroiditis (Hashimoto's), iodine deficiency.
Hyperthyroidism - excess hormones: tachycardia, weight loss, tremor, exophthalmos. The most common cause is Graves disease (diffuse toxic goiter).
Thyroid nodules are found in 50% of people over 60 years of age. In 95% of cases they are benign.
The location of the thyroid gland relative to the trachea, larynx and neck vessels is convenient to study in 3D atlas Humio - rotate the model and examine the topography of the gland.