The word plasma describes two entirely different things depending on your perspective
In the cosmos, plasma is the dominant state of matter, making up 99.9% of the visible universe. Yet, in human biology, it is the straw-colored liquid foundation of your blood. These two distinct definitions share a name but operate in vastly different realms of physics and physiology.
In the vastness of space, plasma is a fundamental state of matter, distinct from solids, liquids, or gases. While it remains the most common form of matter in the visible universe, the term takes on a localized, vital meaning within the human body. Here, plasma is the liquid component of blood, accounting for approximately 55% of its total volume. It is a complex, water-rich solution—comprising 90–92% water—that acts as the primary transport medium for nutrients, waste products, hormones, and essential proteins throughout the body.
The composition of human plasma is a marvel of biological stability. It contains electrolytes like sodium, potassium, and calcium, which must be maintained within extremely narrow ranges to sustain life. For instance, a potassium concentration of only 4 milliequivalents per litre is normal, while a slight increase to 6–7 milliequivalents can be fatal. Beyond electrolytes, plasma is rich in proteins synthesized by the liver and immune system. Albumin, which makes up about 60% of these proteins, is critical for maintaining osmotic pressure, preventing fluid from leaking out of blood vessels into tissues, which would otherwise cause swelling or edema.
Plasma also serves as a sophisticated defense and repair system. Proteins like fibrinogen are essential for clotting, while globulins and the complement system mediate immune responses against pathogens. Clinicians rely on the analysis of plasma—or serum, which is plasma stripped of clotting factors—to diagnose conditions ranging from diabetes to occult malignancies. By transporting everything from oxygen-carrying red blood cells to protective antibodies, plasma functions as the body’s internal highway, ensuring that biological stability, or homeostasis, is preserved across every organ system.
Source: What is Plasma?
