Chapter 6 introduced an essential part of the cell: the. plasma membrane. Thanks to the selective permeability of. phospholipid bilayers and the activity of membrane trans-. port proteins, this structure creates an internal environment. that is different from conditions outside the cell. Our task.
When calcium levels decrease, this stimulates the parathyroid gland to release parathyroid hormone. Parathyroid hormone encourages the normal process of bone breakdown (essential for maintenance and growth of the bone). This process of bone breakdown releases calcium into the bloodstream.
Parathyroid Hormone. Parathyroid hormone is the most important endocrine regulator of calcium and phosphorus concentration in extracellular fluid. This hormone is secreted from cells of the parathyroid glands and finds its major target cells in bone and kidney.Another hormone, parathyroid hormone-related protein, binds to the same receptor as parathyroid hormone and has major effects on development. This effect is mediated by stimulating tubular reabsorption of calcium. 2  Another effect of parathyroid hormone on the kidney is to stimulate loss of phosphate ions in urine.