What influences blood pressure directly?

Fluid balance directly influences blood pressure due to the role that fluids play in the circulatory system. Blood pressure is largely determined by the volume of blood in the bloodstream, which is affected by the amount of fluid retained in the body. When fluid intake is adequate, it helps maintain an optimal blood volume, leading to normal blood pressure. Conversely, if there is an imbalance such as dehydration (low fluid balance), this can result in a decrease in blood volume and consequently lower blood pressure. Alternatively, excessive fluid retention (fluid overload) can cause an increase in blood volume, which raises blood pressure.

In contrast, while factors like body temperature, body alignment, and muscle mass may have indirect effects on blood pressure, they do not have the same direct and immediate impact as fluid balance. For instance, body temperature can influence blood vessel dilation and constriction, body alignment may affect circulation to some degree, and muscle mass contributes to overall metabolism and health but isn't a direct determinant of blood pressure levels compared to fluid balance.