Full Thyroid and Parathyroid Glands (Superior Cross-section View) Description
[Continued from above] . . . It wraps around the anterior portion of the trachea and expands significantly on the lateral sides of the trachea and larynx. The lateral masses are known as the left and right lateral lobes, while the narrower medial region is known as the isthmus.
The parathyroid glands are a collection of four round glands around the size of a grain of rice. These glands are attached to the posterior surface of the lateral lobes of the thyroid gland. Two parathyroid glands (right superior and right inferior) are attached one above the other to the right lateral lobe of the thyroid, while the other two glands (left superior and left inferior) are found on the left lobe.
The thyroid gland produces two vital metabolic hormones – triiodothyronine (T3) and thyroxine (T4). T3 and T4 are produced using iodine, with T3 containing three iodine atoms and T4 containing four. Both T3 and T4 are used to regulate the body’s metabolism by turning on practically every cell in the body and inducing them to produce proteins. The result of the increase in cellular metabolism leads to many physiological effects, including increased heart rate, tissue growth and development, body heat production, and energy consumption.
Calcitonin is also produced by the thyroid gland and works as an antagonist to the only hormone produced by the parathyroid glands, parathyroid hormone (PTH). These two hormones work together to maintain the vital homeostatic balance of calcium ions in the blood, which is essential to the proper function of muscle and nervous tissue. Calcitonin reduces the level of free calcium ions in the blood by reducing the absorption of calcium from food in the intestines; increasing the excretion of calcium ions in the kidneys; and decreasing the activity of osteoclast cells that break down bone matrix to release calcium ions. PTH raises calcium ion levels by increasing calcium absorption in the intestine; decreasing calcium excretion in the kidneys; and increasing the activity of osteoclasts in bones.
Prepared by Tim Taylor, Anatomy and Physiology Instructor