CASR

In one line: The body's calcium thermostat — it keeps blood calcium steady.

CASR (the calcium-sensing receptor) is your body's calcium thermostat: it senses how much calcium is in your blood and adjusts things to keep it in a tight, safe range. This matters because calcium runs your nerves, muscles, and heartbeat — too much or too little is dangerous.

For bone health, the practical point is that calcium alone isn't enough: you need vitamin D to absorb it and vitamin K2 to steer it into bone rather than arteries. The thermostat handles the rest.