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.
The hormones parathyroid hormone (PTH) and calcitonin help regulate blood calcium levels. Calcitonin, secreted by the thyroid gland inhibits osteoclasts and stimulates osteoblasts, thus decreasing blood calcium levels. Parathyroid hormone is secreted by the parathyroid glands, which are on the posterior side of the thyroid. Parathyroid hormone inhibits osteoblasts, stimulates osteoclasts, reduces the output of calcium by the kidneys and promotes the absorption of calcium by the small intestines, thus increasing blood calcium levels.