Low level of sodium ions in the blood and in the extracellular space or as it is referred to by clinicians as hyponatremia is a disorder of sodium ions balance in the body in which there is abnormally low concentration of this ion in the extracellular space below its normal physiological value. This can have several causes that will be mentioned here.
Sodium ion is the most prevalent positively charged ion in the extracellular space. Its counterpart ion inside the cell being potassium ion. Sodium ion balance in the body is regulated by ion pumps which are mecahnisms that require energy and enzymes and which transport these ions against their concentration gradient across the cellular membrane.
The most important ion pump which regulates the transport of sdoium to the outside of the cell is the Na+/K+ ion pump. This pump is responsible for the concentration gradient for sodium ions as well as that for potassium ions across the cellular membrane. There is another pump for sodium but which is less signifcant than this pump and which is called the Na+/Ca++ ion pump.
This pump is more important for calcium ions in promoting muscles contraction. The Na+/K+ ion pump requires energy in the form of ATP moleculesin order to be able to function properly. In addition it requires ATPase enzyme which is a protein enzyme that catalyzes the transport of these ions across the cellular membrane.
For soidun ions the Na+/K+ ion channel is the most important physiologically for the function of sodium ions. Sodium ions are very important along with potassium ions in maintaining normal function of the neurons of the nervous system. Therefore, any disturbance in the concentration of sodium or potassium concentration can be manifested clinically by neurlogical and muscular disorders in the body.
Sodium ion is usually important for initiating the action potential in the neurons. It makes so by inducing a depolarization process in which a signal by a neurotransmitter such as acetylcholine opens sodium ion channels. Thus beginning its flow to the inside of the cell. This process helps to initiate an action potential by increasing the electric potenial of the cellular membrane.
Thi way communication between neurons is done. Due to the importance of sodium ion channels it can be used clinically to induce a state of anesthesia in which blocking of the sodium channel does not allow pain stimuli to propagate from one neurons alon the sensory path of the nervous system.
Thus a sensation of pain is not perceived by the individual. Also agonizing the sodium channel action can induce a continuous action potential. Thus improving the communication between neurns which can lead to sustained stimuli of certain sensations. A decrease in the cocentration of sodium in the extracellular space can be caused for eaxmple due to increased amount of water in the body in which case it is called dilutional hyponatremia.
This is especially obsreved in disorders in which there is excessive conservation of water in the body. This condition can be caused by the effect of excessive amount of the hormone vasopressin as occurs in disorders of the posterior pituitary glandor more often due to malignancy in the body which secretes this hormone in an ectopic manner such as oocurs in lung cancer.
Also a disorder of secreting the hormone aldosterone which is a known regulator of the level of sodium in the body can cause a state of hyponatremia if the level of aldosterone hormone in the blood is deficient. This condition ca cause in addition to hyponatremic states a state of hyperkalemia which can have effect on the heart function.
Also vomitting from the gastrointestinal tract can predispose to a state of hyponatremia which can be corrected by administering saline solution that contains sodium ions intravenously. In addition diarhea or loss of liquids from the body through excessive sweating can cause also hyponatremia with possible dehydration.