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.
Mechanistically, parathyroid hormone preserves blood calcium by several major effects: 1  Stimulates production of the biologically-active form of vitamin D within the kidney. 2  Facilitates mobilization of calcium and phosphate from bone. 3  Maximizes tubular reabsorption of calcium within the kidney.