Thyroid vs Parathyroid
The human endocrine system secretes hormones directly to the circulation, so that these hormones will act on the specific receptors on specific cells to bring about necessary changes required for development in physical and psychological aspects, reproductive life, day to day well being, etc. The central control of the endocrine system is through neural, hormonal and humoral stimuli acting on the hypothalamus, which in turn activates the pituitary gland, which secretes the controller hormones required for the other endocrine glands. This happens most of the time, but not always. The thyroid and parathyroid glands are important components of the whole endocrine system of the human body, they need to be addressed and compared in the anatomical, physiological and pathological terms.
The thyroid gland, which is situated at the front of the neck just below the laryngeal prominence (Adam’s apple), is a single gland with two lobes and a central, connecting isthmus arranged like a butterfly. It has two vessels supplying blood, the superior and the inferior thyroid vessels. The hormonal control of this gland is through a cascade where the hypothalamus secretes thyrotrophin releasing hormone (TRH), which in turn causes the release of thyroid stimulating hormone (TSH), which acts on the thyroid gland to bind iodine to form thyroid hormones T3 and T4. These hormones are important for cellular growth, brain growth and intelligence and the overall well being of the person. A deficit causes hypothyroidism, and an excess causes hyperthyroidism. This gland is also a target for tumours. They range from benign to highly malignant, affecting many decades of life.
The parathyroid glands are usually 4 separate glands, positioned on the posterior surface of the thyroid gland with two each on either lobe. But there may be varied amounts of these glands. These glands are mainly supplied by the inferior thyroid artery. The release of hormones from this gland is not regulated by the hypothalamo-pituitary axis, but by the calcium sensing receptors in the gland. The parathyroid hormone (PTH) causes increases in the serum calcium levels (through acting in the gut, kidneys, bone and Vit.D) and the calcitonin hormone antagonizes the action of PTH. Excess of PTH causes hyperparathyroidism, and the deficit causes hypoparathyroidism. There may be very rare occurrence of malignancies at this site too.
Difference between Thyroid and Parathyroid
Both these structures are endocrine glands, having important functions in the human body. Both are located in the anterior neck, and are related to each other. But the thyroid is a single gland, whereas the parathyroids are 4 or more separate glands. The thyroid has two or more major blood supplies, whereas the parathyroid has a single major blood supply. The thyroid gland is controlled by the hypothalamopituitary axis, but the parathyroid is controlled by Ca2+ sensors on the gland. The thyroid hormones have an effect in almost all the cells in the body, whereas parathyroid hormones are limited to a discrete few tissues. The occurrence of malignancies is very common in the thyroid gland, whereas it is very rare in the parathyroid glands.
In summary, these glands are very important due to the actions of these hormones, and ultimately the well being of the person. They are sometimes interdependent in iatrogenic accidents. That means, on some occasions when the thyroid gland is removed (due to nodule/cancer), the parathyroid are also accidentally removed.