Some science behind the scenes

Electrolyte loss

Channels are found in all cell membranes.  They are tiny.  The archetypal channel pore is just one or two atoms wide at its narrowest point and is selective, accepting only one type of ion, such as sodium, calcium or potassium. These ions move through the channel pore single file nearly as quickly as the ions move through free fluid.

Ion channels are key components in a wide variety of biological processes that involve rapid changes in cells, such as cardiac, skeletal, and smooth muscle contraction, epithelial nutrient transport {epithelial cells are tissue cells that perform functions like  secretion, selective absorption, protection, transcellular transport and detection of sensation), T-cell activation (our system of immunity)  and pancreatic beta-cell insulin release.

As the volume of electrolytes decreases, therefore,  numerous extra physiological effects can then arise affecting the heart muscles, blood vessels,  neurons and so on.

For example, as intracellular calcium decreases there is a reduction in muscle contraction. In the heart, a decrease in calcium available for each beat results in a decrease in cardiac contractility. In blood vessels, a decrease in calcium results in less contraction of the vascular smooth muscle and therefore an increase in arterial diameter [vasodilation].   Vasodilation decreases total peripheral resistance, while a decrease in cardiac contractility decreases cardiac output. Since blood pressure is determined by cardiac output and peripheral resistance, blood pressure drops.  So the overall effect of loss of electrolytes due to dehydration  is to reduce blood pressure!