Systems Biology
The proper balance of calcium levels in our body is crucial as it affects neuron function, muscle contraction, and cell communication, among other things. Calcium homeostasis is managed by two antagonistic hormones: calcitonin and parathyroid hormone (PTH). Calcitonin, produced by C cells in the thyroid gland, lowers serum calcium levels, while PTH is produced in chief cells of the parathyroid glands and raises serum calcium levels.
Calcitonin acts on three types of target cells to lower blood calcium concentration. It increases calcium excretion in the kidneys, increases calcium deposition in bones, and lowers calcium absorption in the intestines. On the other hand, PTH raises calcium concentration by decreasing calcium excretion in kidneys, decreasing calcium deposition in bones, and increasing calcium absorption in intestines. For the last action, PTH needs to activate vitamin D, which is responsible for promoting calcium absorption. Besides, PTH plays a key role in maintaining phosphorus homeostasis by managing phosphate salts in bones, kidneys, and intestines.
Lesson Outline
<ul> <li>Introduction: Importance of calcium homeostasis and the role of parathyroid glands</li> <ul> <li>Calcium levels affect neuron function, muscle contraction, and cell communication</li> <li>Calcium homeostasis managed by calcitonin (produced by C cells in thyroid gland) and parathyroid hormone (PTH) (produced by cheif cells in the parathyroid glands)</li> </ul> <li>How calcitonin and PTH maintain calcium homeostasis</li> <ul> <li>Calcitonin's three ways to lower blood calcium concentration</li> <ul> <li>Targets kidneys to increase calcium excretion</li> <li>Targets bones to increase calcium deposition</li> <li>Targets intestines to lower calcium absorption</li> </ul> <li>PTH's three ways to raise calcium concentration</li> <ul> <li>Targets kidneys to decrease calcium excretion</li> <li>Targets bones to decrease calcium deposition and increase resorption</li> <li>Targets intestines to increase calcium absorption by activating vitamin D</li> </ul> </ul> <li>Phosphorus homeostasis and PTH</li> <ul> <li>PTH increases osteoclast activity releasing phosphate salts from bones</li> <li>In bone, PTH activates osteoblasts to rebuild bone</li> <li>In kidneys, PTH increases phosphate excretion</li> <li>In intestines, vitamin D activated by PTH increases phosphate absorption</li> </ul>
Don't stop here!
Get access to 71 more Systems Biology lessons & 8 more full MCAT courses with one subscription!
FAQs
Parathyroid glands are small endocrine glands located behind the thyroid gland in the neck. There are typically four of these glands, and they play a crucial role in maintaining calcium homeostasis by producing parathyroid hormone (PTH). PTH regulates the levels of calcium in the blood by promoting bone resorption, increasing calcium reabsorption in the kidneys, and activating vitamin D synthesis, which in turn enhances intestinal calcium absorption.
Calcitonin and parathyroid hormone (PTH) have opposite effects on calcium balance in the body and work together to maintain calcium homeostasis. Produced by the thyroid gland, calcitonin lowers blood calcium levels by inhibiting bone resorption through osteoclast inhibition and decreasing the reabsorption of calcium in the kidneys. Conversely, PTH increases blood calcium levels by promoting bone resorption, enhancing calcium reabsorption in the kidneys, and stimulating vitamin D synthesis. The balanced actions of these two hormones ensure that calcium levels are maintained within a narrow range that is necessary for various physiological processes.
Cell communication is essential in the maintenance of calcium homeostasis, as signaling pathways within and between cells allow for the regulation and response to changes in calcium levels. For instance, the parathyroid glands sense changes in blood calcium levels due to specialized cells called chief cells, which communicate the need to either increase or decrease parathyroid hormone secretion. Additionally, cells within bones, kidney tubules, and the gastrointestinal tract receive and respond to signaling molecules such as PTH, calcitonin, and vitamin D, enabling them to modulate calcium metabolism and maintain homeostasis.
Bone formation and vitamin D are both essential components of calcium homeostasis. Bones serve as the primary reservoir for calcium in the body, and processes such as bone formation (ossification) and breakdown (resorption) enable the mobilization of calcium to maintain blood calcium levels within the required range. Vitamin D, on the other hand, contributes to calcium homeostasis by enhancing the absorption of dietary calcium in the gastrointestinal tract. When activated by PTH in the kidneys, vitamin D increases the expression of calcium transport proteins in the intestines, which facilitates the entry of calcium into the bloodstream. This helps raise blood calcium levels and maintain homeostasis.
