Anatomy Physiology

Hypophosphatemia is a disorder of phosphate ions balance in the blood in which the concentration of the phosphate ions is lower than a normal value.  This has several causes as will be discussed later.  The importance of phosphate ion stem s from the fact that it is incorporated into the energy rich ATP molecule.  ATP is the energy currency of the cells that drive many unfavourable biochemical reactions to completion which otherwise do not go without the assitance of ATP

ATP molecules contain energy rich phosphoanhydride bonds which upon hydrolysis release energy that is taken up by different reactions in the body.  Phosphorus atom is involved in many metabolic reactions whether anabolic or catabolic.  For example, it is involved in enzyme regulation by adding or taking phophate group to the enzyme that is involved in the regulation process. 

It is also involved in energy transformation and storage.  The molecule 2,3 bisphosphoglycerate is involved in the delivery of oxygen to body tissues.  It contains two phosphate groups.  In the case of hypophosphatemia this molecule does not function properly.  Therefore the mechanism by which oxygen is transported to the cells of the tissues is impaired. 

The phosphorus atom is also involved in urinary buffering of acids.  It is also involved in supporting the function of white blood cells to fight infection by providing sufficient amount of ATP.  It is also involved in the synthesis of calcitriol, the active form of vitamin D. 

There are several causes to the existence of hypophosphatemia.  Among these causes is hyperparathyroidism.  The parathyroid hormone causes as one of its biological effects excessive urination of phophate ions in addition to its physiological role in bone resorption and increase in calcium level in the blood.  Thus contributing to low level of of phosphate in the blood.

Acidosis is also a factor that induces hypophophatemia by inducing phosphate excretion in the kidneys.  Cortisol the hormone that is secreted by the adrenal cortex, also induces a state of hypophosphatemia by increasing the amount of phophate ions in the urine.  Removal of the adrenal glands leads to increased phosphorus reabsorption in the kidney tubules. 

Vitamin D or calcitriol has also an effect on conservation of phosphorus by increasing the reabsorption rate in the kidney tubules.  Alcoholism or administration of alcohol can lead to hypophosphatemia.  It is well known that ethanol has an effect on inhibiting the action of the hormone vasopressin or antidiuretic hormone.  Thus causing a state of increased urination and depletion of phosphate in the urine. 

Magnesium deficiency leads to depletion of phosphate ions in the urine.  Hypocalcemia induces a state of hypophosphatemia by inducing hyperparathyroidism which stimulates the the excretion of phosphate in the urine.  Ketoacidosis which is part of type I diabetes mellitus complications can lead to hypophosphatemia by increasing the urinary output of phosphate ions.  This is not surprising since acids stimulate the urination of phosphate and ketoacids are also acids in addition to their being ketone bodies.