What is the Blood Plasma | Composition | Functions

When we think about blood, the first things that often come to mind are red blood cells or perhaps white blood cells. But there’s another essential component that often goes unnoticed—blood plasma. It makes up more than half of our blood and plays a vital role in keeping us alive and healthy. Let’s explore what blood plasma is, what it does, and why it matters.

What is the Blood Plasma?

Blood plasma is the yellowish liquid portion of blood in which the blood cells are suspended. It accounts for about 55% of the total blood volume. While it may look simple, plasma is a complex fluid made up mostly of water, along with proteins, electrolytes, hormones, nutrients, and waste products. This combination helps transport essential substances throughout the body.

History of Plasma Discovery

The story of plasma begins in the 17th century, when scientists first started to examine blood under microscopes. However, they could only see the solid parts, red blood cells and white blood cells, floating in a fluid that remained poorly understood.

It wasn’t until the 19th century that researchers began to study this liquid portion more closely. In 1863, the Czech physiologist Ernst Brücke was the first to use the word plasma to describe the clear, yellowish fluid that remained after blood cells were removed.

Origin of the Word "Plasma"

The word plasma comes from the Greek word plásma (πλάσμα), which means “something molded or formed.” Brücke chose this term because he saw plasma as the material in which the blood cells were "molded" or suspended, much like clay can hold a form.

Later, as medical research advanced, the name stuck and became the standard term for this fluid part of blood. One should ask that why it is called plasma? It is called plasma because:

• Forming medium: Plasma acts as the formative substance that carries and supports blood cells, giving structure to the liquid portion of blood.
• Biological resemblance: Just as plasma in physics (ionized gas) is a medium filled with active particles, blood plasma is a medium filled with vital substances like proteins, hormones, and nutrients.
• Historical context: Brücke used the word in analogy to how plasma (in Greek) means “something that can be shaped or molded,” since blood cells are suspended and “shaped” by this fluid.

Milestones in Plasma Research

• 1901: Karl Landsteiner discovered blood groups (A, B, AB, O), which later made plasma transfusions safer.
• 1930s–40s: Plasma gained worldwide attention during World War II, when it was used as a blood substitute for soldiers because it could be stored longer and didn’t require strict blood-type matching like red cells.
• Modern era: Today, plasma is the foundation for advanced medical treatments, including clotting factor therapies, immunoglobulin infusions, and plasmapheresis.

Composition of Blood Plasma

Blood plasma is a dynamic mixture of substances, each playing a unique role in maintaining life. Its composition can be broken down into several major components:

1. Water (90–92%)

Water is the main ingredient of plasma, forming the medium in which all other components are dissolved or suspended. It ensures that nutrients, gases, and waste products can move easily around the body. It also helps regulate body temperature by absorbing and distributing heat.

2. Plasma Proteins (7–8%)

Proteins are the most important solid components of plasma and serve multiple purposes:

Albumin

The most abundant plasma protein. It helps maintain the osmotic pressure of blood, which prevents excessive fluid loss into tissues and keeps blood volume stable. It also acts as a carrier protein for hormones, fatty acids, and medications.

Globulins

These are divided into alpha, beta, and gamma globulins. Alpha and beta globulins transport lipids, iron, and fat-soluble vitamins, while gamma globulins function as antibodies, defending the body against infections.

Fibrinogen

A key protein involved in blood clotting. When an injury occurs, fibrinogen is converted into fibrin, which forms a mesh to stop bleeding.

3. Electrolytes and Minerals

Plasma contains essential ions such as sodium, potassium, calcium, magnesium, chloride, bicarbonate, and phosphate. These electrolytes help regulate the pH of the blood, control nerve and muscle function, and maintain fluid balance across cell membranes. For example, sodium is crucial for controlling blood pressure, while calcium is necessary for muscle contraction and clotting.

4. Nutrients

Plasma delivers the building blocks of energy and repair to every cell in the body. It carries:

• Glucose: the body’s primary energy source.
• Amino acids: used to build proteins and repair tissues.
• Lipids (fats and cholesterol): transported in combination with proteins (as lipoproteins) to provide energy and form cell membranes.
• Vitamins: especially water-soluble vitamins like Vitamin C and B-complex, which travel directly in plasma.

5. Hormones and Enzymes

Hormones such as insulin, cortisol, and thyroid hormones circulate in plasma to regulate body processes like metabolism, growth, and stress responses. Enzymes, meanwhile, act as catalysts to accelerate chemical reactions in the body.

6. Gases

Plasma helps transport respiratory gases. Although most oxygen is carried by red blood cells, a small amount dissolves directly in plasma. Carbon dioxide, on the other hand, is carried partly dissolved in plasma and partly in the form of bicarbonate ions.

7. Waste Products

Plasma also acts as the body’s waste removal system. It carries byproducts such as urea, uric acid, creatinine, and bilirubin to the kidneys, liver, and lungs for elimination. This prevents toxic buildup in the body.

Functions of Blood Plasma

Plasma is more than just a transport medium. It is a multifunctional fluid essential for survival. Its functions can be broken down into several categories:

1. Transportation of Substances

One of the most important functions of plasma is to carry materials around the body. It transports:

1. Nutrients (glucose, amino acids, vitamins, and lipids) from the digestive system to body cells.
2. Oxygen (small amounts dissolved in plasma) and carbon dioxide (mostly as bicarbonate) for respiration.
3. Hormones from endocrine glands to target organs, ensuring proper communication and regulation of body functions.
4. Waste products such as urea, uric acid, and lactic acid to the kidneys and liver for elimination.

Without plasma, our organs and tissues would never receive the supplies they need, nor could they remove toxins effectively.

2. Blood Clotting and Wound Healing

Plasma proteins like fibrinogen, prothrombin, and clotting factors are essential for blood clotting. When an injury occurs:

Platelets and clotting proteins in plasma gather at the site. Fibrinogen is converted into fibrin threads that form a mesh, trapping blood cells and creating a clot.

This prevents excessive blood loss and forms the foundation for tissue repair.

In patients with clotting disorders (like hemophilia), donated plasma provides these missing clotting factors.

3. Immunity and Defense

Plasma is a key player in the immune system. It contains:

1. Antibodies (immunoglobulins) that recognize and neutralize pathogens.
2. Complement proteins, which help antibodies destroy bacteria.
3. Carrier proteins, which deliver immune cells to sites of infection.

Through these mechanisms, plasma forms the first line of defense against infections and diseases.

4. Maintaining pH and Electrolyte Balance

Plasma keeps the internal environment stable by regulating:

1. pH balance: Plasma contains bicarbonate ions that act as a buffer, preventing blood from becoming too acidic or too alkaline. The ideal blood pH is about 7.35–7.45, and plasma helps maintain this range.
2. Electrolyte balance: Plasma maintains correct levels of sodium, potassium, calcium, and chloride. This balance is essential for nerve impulses, muscle contractions, and hydration.

Even small shifts in plasma electrolyte levels can cause severe problems such as dehydration, seizures, or irregular heartbeats.

5. Regulation of Body Temperature

Because plasma is made up mostly of water, it has a high heat capacity. It can absorb, store, and distribute heat around the body. When we are overheated, plasma transports heat to the skin, where it is released as sweat. When we are cold, it conserves heat by reducing blood flow to the skin. This makes plasma an important player in thermoregulation.

6. Maintaining Blood Pressure and Volume

The protein albumin in plasma maintains oncotic pressure (a form of osmotic pressure). This prevents excessive fluid from leaking into tissues and ensures that blood volume and pressure remain stable. Without this, we would experience dangerous swelling (edema) or low blood pressure (hypotension).

7. Serving as a Communication Network

Plasma functions like the body’s postal system, carrying hormones, chemical signals, and enzymes to different organs. For example:

• Insulin travels via plasma to regulate blood sugar levels.
• Stress hormones like cortisol are carried to tissues to trigger emergency responses.
• Growth factors circulate to promote healing and cell repair.

This ensures that the body works as a coordinated unit rather than as separate organs acting independently.

Medical Importance of Blood Plasma

Blood plasma is not just vital for our everyday functioning. It also has tremendous medical importance. Because it contains proteins, antibodies, and clotting factors, plasma has been used in a wide range of lifesaving therapies. Below are some of the most important medical applications of plasma:

1. Plasma Transfusions

In emergencies such as massive blood loss, shock, or severe burns, patients may receive plasma transfusions. Plasma helps:

• Restore blood volume and stabilize blood pressure.
• Replenish clotting factors to stop bleeding.
• Replace lost proteins such as albumin to prevent fluid leakage into tissues.

This is often given in trauma care, during major surgeries, or after accidents.

2. Treatment of Clotting Disorders

Plasma is an essential treatment for people with hemophilia and other clotting disorders. These patients lack certain clotting factors and are at high risk of dangerous bleeding. Plasma transfusions or plasma-derived medications provide:

• Factor VIII or Factor IX concentrates for hemophilia A and B.
• Fibrinogen replacement for patients with rare fibrinogen deficiency.
• Prothrombin complex concentrates to help prevent uncontrolled bleeding.

3. Immune System Support

Plasma is a rich source of immunoglobulins (antibodies), which can be isolated and used as therapy. These are given as Intravenous Immunoglobulin (IVIG) to treat:

• Primary immune deficiencies (when the body cannot produce enough antibodies).
• Autoimmune diseases such as Guillain-Barré syndrome or multiple sclerosis.
• Serious infections where extra immune support is needed.

IVIG therapy boosts or modulates the immune system, often saving lives in patients with weak or misdirected immunity.

4. Convalescent Plasma Therapy

During outbreaks of infectious diseases (such as COVID-19, Ebola, or SARS), plasma from recovered patients has been used as a therapy. Known as convalescent plasma therapy, it provides antibodies that help fight the infection in sick patients. 

While its effectiveness can vary, it has offered hope in times when no other treatments were available.

5. Plasma Exchange (Plasmapheresis)

Plasma can also be removed and replaced in a process called plasmapheresis. This is used in conditions where harmful substances circulate in plasma, such as:

• Autoimmune diseases (e.g., lupus, myasthenia gravis, or multiple sclerosis), where damaging antibodies are removed.
• Neurological disorders, where abnormal proteins affect nerve function.
• Blood disorders, where toxic substances in plasma are filtered out.

In this process, the patient’s plasma is separated from blood cells and replaced with donor plasma or a plasma substitute.

6. Albumin Therapy

Albumin extracted from plasma is used to:

• Treat patients with severe burns, where plasma loss leads to dehydration and shock.
• Manage liver disease, where albumin levels are dangerously low.
• Stabilize patients with hypovolemic shock (low blood volume).
• Albumin helps maintain blood pressure and keeps fluids from leaking into tissues.

7. Plasma in Diagnostics and Research

Plasma is also critical in medical research and diagnostics. It is used to:

• Detect markers of diseases (such as glucose for diabetes or cholesterol for heart disease).
• Study infections by analyzing antibodies present in plasma.
• Develop new therapies, including plasma-derived drugs.

8. Plasma Donation and Blood Banks

Plasma donation is as important as blood donation. Donated plasma can be frozen and stored as Fresh Frozen Plasma (FFP) for up to a year. Plasma donations provide the raw material for:

• Lifesaving transfusions.
• Plasma-derived medicines (like clotting factors and IVIG).
• Emergency stockpiles for hospitals.

In many countries, plasma donations are highly encouraged because plasma-based therapies are in constant demand.

Why Plasma Matters in Medicine

Plasma is more than just the fluid part of blood, it is a lifesaving resource. From trauma care and surgery to the treatment of rare immune disorders, plasma therapies have revolutionized modern medicine. 

Without plasma donations, millions of patients with genetic, infectious, and chronic diseases would have no treatment options.

Plasma vs serum

Although plasma and serum are both the liquid parts of blood, they are not the same. 

Plasma is the fluid portion of blood that contains clotting factors such as fibrinogen, prothrombin, and other proteins, along with nutrients, hormones, and waste products.

In contrast, serum is the liquid that remains after blood has clotted, which means it does not contain clotting factors because they are consumed during the clotting process. 

Their differences are compiled in the table below:

Conclusion

Blood plasma is far more than a background fluid—it is the life-supporting medium that sustains, protects, and heals us. From carrying nutrients and defending against infections to saving lives in hospitals through plasma transfusions, this golden liquid is indispensable.

By understanding its composition, history, medical importance, and difference from serum, we can better appreciate the role plasma plays in both everyday health and lifesaving treatments.

Some Short Questions and Answers

1. What is blood plasma?

A. Blood plasma is the yellowish liquid portion of blood that makes up about 55% of its volume. It carries blood cells, proteins, nutrients, hormones, and waste products throughout the body.

2. What is plasma made of?

A. Plasma is mostly water (about 90–92%), along with proteins (such as albumin, globulins, and fibrinogen), electrolytes, nutrients, hormones, gases, and waste products.

3. What does plasma do in the body?

A. Plasma transports nutrients, hormones, and waste; helps with blood clotting; maintains pH and fluid balance; regulates temperature; and supports the immune system with antibodies.

4. Why is blood plasma important in medicine?

A. Plasma is used in transfusions, to treat clotting disorders like hemophilia, to provide antibodies in immune therapy, and in procedures like plasma exchange for autoimmune diseases.

5. How is plasma different from serum?

A. Plasma contains clotting factors, while serum is the fluid left after blood clots and therefore lacks clotting proteins like fibrinogen.