A significant loss of circulating blood volume leads to decreased venous return to the heart, which reduces cardiac preload and stroke volume. The body compensates initially by activating the sympathetic nervous system, causing tachycardia and peripheral vasoconstriction to maintain blood flow to vital organs. The neuroendocrine system helps respond to hypovolemia by increasing the secretion of antidiuretic hormone (ADH) from the posterior pituitary gland. ADH also promotes salt and water resorption. If the volume loss continues and these compensatory mechanisms become overwhelmed, the patient becomes hypotensive and acidotic.