Paratüroidnäärmetes

Paratüroidnäärmetes, also known as parathyroid glands, are four small endocrine glands located in the neck, usually found behind the thyroid gland. These glands play a crucial role in regulating calcium levels in the bloodstream. Each parathyroid gland is about the size of a grain of rice and is composed of chief cells and oxyphil cells. The primary function of the parathyroid glands is the secretion of parathyroid hormone (PTH). PTH is a peptide hormone that acts on several target organs, including bones, kidneys, and the small intestine, to increase calcium levels. When blood calcium levels drop, the parathyroid glands release more PTH. This hormone stimulates osteoclasts in the bone to release stored calcium into the blood. In the kidneys, PTH promotes the reabsorption of calcium from the urine back into the bloodstream and also stimulates the production of calcitriol, the active form of vitamin D. Calcitriol, in turn, enhances the absorption of calcium from the small intestine. Conversely, when blood calcium levels rise, PTH secretion is suppressed, leading to a decrease in calcium release from bones and increased calcium excretion by the kidneys. Disruptions in parathyroid gland function can lead to significant health issues, such as hyperparathyroidism, where there is excessive PTH production, causing high blood calcium levels, or hypoparathyroidism, characterized by insufficient PTH production and low blood calcium levels.