Final answer:
Total calcium in human plasma exists in three physiological states: ionized calcium, protein-bound calcium predominantly attached to albumin, and calcium complexed with organic acids, phosphate, and citrate. These forms are maintained in equilibrium, regulated by PTH, vitamin D, and calcitonin.
Step-by-step explanation:
In human plasma, total calcium exists in three physiological states. These states include:
- Ionized calcium, which constitutes about 55-65% of the total calcium in plasma and is crucial for important body functions like muscle contraction and blood coagulation.
- Protein-bound calcium, which accounts for about 35-45% of plasma calcium, with the majority bound to albumin. This fraction is non-diffusible through vascular walls due to its size.
- Calcium complexed with organic acids, phosphate, and citrate, making up 5-10% of the total calcium. These complexes can increase in conditions such as renal failure.
All these forms of calcium are in a state of equilibrium with each other, and an imbalance can lead to various health issues. PTH (parathyroid hormone), vitamin D, and calcitonin are hormones that help maintain calcium homeostasis through their effects on bones, the digestive system, and the kidneys.