Final answer:
Cardiac output falls first in cardiogenic shock, and this leads to the activation of the renin-angiotensin-aldosterone system as a compensatory response.
Step-by-step explanation:
In cardiogenic shock, cardiac output falls first due to the inability of the heart to maintain adequate circulation. This event subsequently triggers the activation of the renin-angiotensin-aldosterone system (RAAS). The RAAS is a crucial regulatory mechanism that addresses decreased blood pressure and volume.
Specialized cells in the kidneys, called juxtaglomerular (JG) cells, secrete renin, which converts angiotensinogen (produced by the liver) into angiotensin I.
This, through the action of angiotensin-converting enzyme (ACE), becomes angiotensin II—a potent vasoconstrictor that also stimulates aldosterone and ADH release, leading to an increase in blood pressure and volume. However, this compensatory mechanism comes into play after the initial fall in cardiac output that characterizes cardiogenic shock.