What can cause shock in a patient?

Decreased plasma volume is a significant factor that can lead to shock in a patient because it directly affects the circulatory system's ability to maintain adequate blood flow and pressure. When the plasma volume is reduced, typically due to conditions like dehydration, severe bleeding, or certain medical conditions, there is less fluid available in the vascular system. This can result in a drop in blood volume, which in turn decreases venous return to the heart, leading to reduced cardiac output. As the body's organs and tissues become deprived of oxygen and nutrients, this can precipitate a state of shock, where the body struggles to cope with the diminished circulation.

In the context of the other options, while exercise typically increases blood flow and can lead to a temporary increase in cardiac output, it does not cause shock unless accompanied by other factors. Nutrition deficiency, while it can lead to broader health issues over time, does not directly result in shock. Social isolation may impact mental health but does not physiologically induce shock in the body. Thus, decreased plasma volume stands out as the most direct and physiologically relevant cause of shock.