Each body system is dependent on one another in some way. The skeletal system is dependent on the muscle system for movement, the respiratory system is dependent on the circulatory system, etc. If one body system were to fail, the other body systems dependent on it would struggle to complete their functions as normal. Blood pressure either falls or rises, their oxygen levels drop, and the more their body systems struggle to complete their functions, the more tired they get and they eventually give up. This is what causes septic shock, which is when all organs fail and blood pressure decreases because of an infection.
