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
Blood type (non-human) Ideally, cross-matching should be performed prior to transfusion, or a universal donor may be used. The ideal universal whole blood donor is a non-thoroughbred gelding that is Aa, Ca, and Qa negative. If this is not available, a gelding, preferably of the same breed as the patient, may be used as a donor, and cross-matching may be crudely accessed by mixing donor serum with patient blood. If the mixture agglutinates, the donor blood contains antibodies against the blood of the patient, and should not be used. The polymorphic systems in cattle include the A, B, C, F, J, L, M,