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.
Thyroid-stimulating hormone (TSH) is produced by the pituitary gland, a tiny organ located below the brain and behind the sinus cavities. TSH stimulates the thyroid gland to release the hormones thyroxine (T4) and triiodothyronine (T3) into the blood. These thyroid hormones help control the rate at which the body uses energy. This test measures the amount of TSH in the blood. TSH, along with its regulatory hormone thyrotropin releasing hormone (TRH), which comes from the hypothalamus, is part of the feedback system that the body uses to maintain stable amounts of thyroid hormones in the blood.