The Components of Blood and Their Functions In The Body

This post is about the components of blood and their functions. First lets talk about the blood.

What is Blood?

Blood is both a tissue and a fluid. This is because the blood is a collection of similar specialized cells that serve particular functions. These cells are suspended in a liquid matrix called plasma which makes the blood a fluid. The blood is a transport liquid pumped by the heart to all parts of the body, after which it is returned to the heart to repeat the process.

The Components of Blood

In humans, blood is an opaque red fluid, freely flowing but denser and more viscous than water. The characteristic color is imparted by hemoglobin, a unique iron-containing protein.

the blood cells

Hemoglobin brightens in color when saturated with oxygen and darkens when oxygen is removed. For this reason, the partially deoxygenated blood from a vein is darker than oxygenated blood from an artery.

The red cells constitute about 45 percent of the volume of blood, and the remaining cells such as white blood cells and platelets constitutes less than one percent.

The fluid portion known as plasma, is a clear, slightly sticky, yellowish liquid. After a fatty meal, plasma transiently appears turbid.

Within the body the blood is permanently fluid, and turbulent flow assures that cells and plasma are fairly homogeneously mixed.

the components of blood, the blood components

The components of blood are namely:

  • Plasma
  • Red Blood Cells
  • White Blood Cells
  • Platelets

The Plasma

The liquid portion of the blood is the plasma. It is a complex solution containing more than 90 percent of water. Of all the constituents of plasma, proteins are the most abundant, making up about 7 percent of the plasma by weight. In fact, the principal difference between the plasma and the extracellular fluid of the tissues is the high protein content of the plasma.

Functions of The Plasma

The functions of blood plasma:

  • Plasma serves as a transport medium for delivering nutrients to the cells of the various organs of the body.
  • It transports waste products derived from cellular metabolism to the kidneys, liver, and lungs for excretion.
  • It is also a transport system for blood cells.
  • It plays a critical role in maintaining normal blood pressure.
  • Plasma helps to distribute heat throughout the body and to maintain homeostasis including acid-base balance in the blood and body.
  • The water of the plasma is freely exchangeable with that of body cells and other extracellular fluids and is available to maintain the normal state of hydration of all tissues.

The Red Blood Cells

The red blood cells are highly specialized, well adapted for their primary function of oxygen transport. Each red blood cell is a package of hemoglobin molecules. Hemoglobin is the red iron-containing pigment that carries oxygen in the blood.

Functions of the red blood cells:

  • Red blood cells contains hemoglobin, which transports oxygen from the lungs to all parts of the body.
  • It has no nucleus and has more space to carry hemoglobin and oxygen.
  • It has a circular biconcave shape. This increases the surface to volume ratio and therefore oxygen can diffuse in and out at a more efficient and faster rate.
  • It has a thin outer membrane to let oxygen diffuse through easily.
  • The red cell is also capable of transporting carbon dioxide (CO2) from the periphery to the lungs.

The White Blood Cells

White blood cells are also known as leukocytes. Unlike red cells, white blood cells are nucleated, independently motile, and lack hemoglobin.

Functions of the white blood cells:

  • They defend the body against infection and disease.
  • They ingest foreign materials and cellular debris destroying infectious agents and cancer cells.
  • They also have some reparative functions.
  • They do not undergo cell division in the bloodstream.

The Platelets

The blood platelets are the smallest cells of the blood, averaging about 2-4 micrometers in diameter.

Although much more numerous than the white cells, they occupy a much smaller fraction of the volume of blood because of their relatively minute size. Like the red cells, platelets lack a nucleus and are incapable of cell division, but they have a more complex metabolism and internal structure.

When seen in fresh blood they appear spheroid but they have a tendency to extrude hairlike filaments from their membranes. They stick to each other but not to red cells and white cells. Tiny granules within platelets contain substances important for the clot-promoting activity of platelets.

Functions of the platelets:

  • The function of the platelets is related to hemostasis, the prevention and control of bleeding.
  • Platelets stops the bleeding when there’s injury by forming a blood clot on the surface.
  • Platelets also contribute substances essential for the normal coagulation of the blood, and they cause a clot to shrink after it has been formed.


The blood is a fluid tissue that has four components. They are plasma, red blood cells, white blood cells, and platelets. Plasma makes up the liquid part of the blood while red cells have hemoglobin that carries oxygen throughout the body. White blood cells attack and destroy foreign objects that enter the body. Platelets helps the blood to clot when there’s injury.


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