Sodium in biology mEq/liter (135 - 145 mmol/L). A serum sodium level of less than 135 mEq/L qualifies as hyponatremia, which is considered severe when the serum sodium level is below 125 mEq/L. The renin–angiotensin system and the atrial natriuretic peptide indirectly regulate the amount of signal transduction in the human central nervous system, which depends on sodium ion motion across the nerve cell membrane, in all nerves. Sodium is thus important in neuron function and osmoregulation between cells and the extracellular fluid; the distribution of sodium ions are mediated in all animals by sodium–potassium pumps, which are active transporter solute pumps, pumping
Serum iron the lab techniques used; look at the individual laboratory reference values to interpret a specific test (for instance, your own). Serum iron Serum iron is a medical laboratory test that measures the amount of circulating iron that is bound to transferrin (90%) and serum ferritin (10%). Clinicians order this laboratory test when they are concerned about iron deficiency, which can cause anemia and other problems. 65% of the iron in the body is bound up in hemoglobin molecules in red blood cells. About 4% is bound up in myoglobin molecules. Around 30% of the iron in the body is stored