Final answer:
Hypernatremia is characterized by an excessive concentration of sodium in the blood, caused by either exogenous factors like diet or medical treatment, or endogenous factors like hormonal imbalances involving ADH and aldosterone.
Step-by-step explanation:
The two main categories of causes of hypernatremia, an abnormal increase in blood sodium, are exogenous and endogenous. Exogenous causes refer to external factors that contribute to increased sodium levels, such as dietary intake or medical treatments like intravenous saline solutions. Endogenous causes are internal factors and may include hormonal imbalances involving ADH (antidiuretic hormone) and aldosterone which regulate sodium and water balance in the body. In hypernatremia, high levels of sodium in the blood can result from water loss from the blood, leading to hemoconcentration of all blood constituents or from the retention of sodium due to hormonal influences.