Divalent magnesium and calcium ions play a crucial role in maintaining ion balance in biological fluids. These ions are present in large proportions in various bodily fluids, including blood, extracellular fluid, and intracellular fluid.

Importance of Ion Balance:
Maintaining proper ion balance is essential for the normal functioning of cells and organs in the body. It helps in various physiological processes and is crucial for maintaining overall health and homeostasis.

Role of Magnesium and Calcium Ions:
Divalent magnesium and calcium ions contribute significantly to maintaining ion balance in biological fluids. They perform various functions that are necessary for the proper functioning of the body.

1. Enzymatic Reactions:
Magnesium ions act as cofactors for numerous enzymatic reactions in the body. These reactions are involved in energy production, DNA replication, protein synthesis, and many other essential processes. Calcium ions also play a role in activating certain enzymes and regulating their activity.

2. Membrane Potential:
Magnesium and calcium ions are involved in establishing and maintaining the membrane potential of cells. The membrane potential is the electrical charge difference across the cell membrane, which is essential for the transmission of nerve impulses, muscle contraction, and other electrical signaling processes.

3. Muscle Contraction:
Calcium ions are particularly important for muscle contraction. When a muscle is stimulated, calcium ions are released from the sarcoplasmic reticulum in muscle cells. These ions bind to proteins involved in muscle contraction, leading to the sliding of actin and myosin filaments and muscle contraction.

4. Nerve Function:
Both magnesium and calcium ions are involved in proper nerve function. Calcium ions participate in the release of neurotransmitters from nerve endings, which is essential for transmitting signals between nerve cells. Magnesium ions regulate the activity of N-methyl-D-aspartate (NMDA) receptors, which are involved in learning, memory, and synaptic plasticity.

5. Ion Transport:
Magnesium and calcium ions also contribute to the transport of other ions across cell membranes. They play a role in regulating the permeability of ion channels, which are responsible for the movement of ions in and out of cells. This regulation is crucial for maintaining the proper balance of ions, such as sodium, potassium, and chloride, which are essential for various cellular processes.

Conclusion:
In summary, divalent magnesium and calcium ions are found in large proportions in biological fluids due to their vital roles in maintaining ion balance. Their functions include enzymatic reactions, establishment of membrane potential, muscle contraction, nerve function, and ion transport. The presence of these ions in appropriate concentrations is crucial for the normal functioning of cells, tissues, and organs in the body.