# Calcium (Ca$^{++}$) --- **Calcium ion** or **Ca$^{++}$** is a very important [[ion]] that acts as an [[electrolytes|electrolyte]] whose primary functions include keeping the heart's [[autorhythmic cells|pacemaker cells]] going and forming blood clots, as well as initiating [[muscle twitch|muscle contractions]] and facilitating exocytosis of molecules from cells (including neurons). Calcium also plays a role in [[coagulation]]. Not enough calcium ([[hypocalcemia]]) results in **calcium tetany**, or twitching and spasms due to lack of calcium, and too much calcium ([[hypercalcemia]]) results in **calcium rigor**, or an inability of the muscles (including heart muscles!) to relax. Fortunately, as calcium levels are tightly regulated in the body (see below), instances of those issues are rare. >[!science] Normal Values > The normal value of Ca++ is **8.4 -10.5** mg/dL >>[!abstract]- Visualization >>![[metabolic panel values.png]] A fair amount of calcium in the blood binds to [[albumin]]. This is "serum calcium" which is pretty easy to measure but it's not "ionized calcium" which the active form that we can easily use. Unfortunately it's more difficult to measure in the lab, so unless they say so specifically we don't get "ionized calcium" in the lab value. - Serum calcium has a *direct* relationship with [[magnesium]] (i.e. when calcium levels rise, magnesium levels also rise, and vice versa). - Serum calcium has an *indirect* relationship with [[phosphate]] (i.e. when calcium levels rise, phosphate levels fall, and vice versa). - [[Vitamin D]] is essential for the absorption of dietary calcium. ## Elemental Calcium **Calcium** is the most abundant [[mineral]] in our bodies—it comprises about ~2% of our body weight! Roughly 99% of that is stored in our [[bone|bones]] and [[teeth]], where it maintains their solid yet flexible structure in the form of [[bone#Hydroxyapatites|hydroxyapatites]]. The rest of the 1% of our calcium lives in the blood (referred to as "serum calcium") and soft tissues. ## Calcium Regulation Calcium is regulated primarily by the [[thyroid|thyroid and parathyroid]] in the form of two hormones, calcitonin and parathyroid hormone. Calcium is [[acids and bases|alkaline]], and thus maintaining the levels in the bloodstream is important to our [[acid-base balance]]. - [[thyroid#Physiology|calcitonin]] is produced by the thyroid and *lowers* the level of serum calcium - activates [[bone cells|osteoblasts]] which uptake serum calcium and put it into the bones - [[parathyroid hormone]] is produced by the parathyroid and *raises* the level of serum calcium. PTH is activated by [[vitamin D]]. - activates [[bone cells|osteoclasts]] and pull calcium out of the bones - increases absorption of dietary calcium in the intestines - increases reabsorption of calcium in the kidneys ![[calcium homeostasis.png]] ## Problems with Calcium - [[hypercalcemia]] is a state with too much calcium in the blood - [[hypocalcemia]] is a state with too little calcium in the blood ___