Health
Fact-checked

At WiseGEEK, we're committed to delivering accurate, trustworthy information. Our expert-authored content is rigorously fact-checked and sourced from credible authorities. Discover how we uphold the highest standards in providing you with reliable knowledge.

Learn more...

What is Blood Composition?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

Blood composition is the chemical composition of blood. Chemically, blood is extremely complex and it varies between different species, especially between vertebrates and invertebrates. Understanding normal blood composition is an important aspect of medical care because it allows doctors to identify situations in which the blood composition is abnormal. Abnormalities in the blood can provide clues to a patient's overall health and may explain symptoms experienced by the patient.

All told, blood makes up about eight percent of body weight. It consists of plasma and cells which move in a suspension through the body. Around 55% of the blood is plasma, and plasma itself is mostly water. The cells in the blood include thrombocytes, erythrocytes, and leukocytes, all of which serve different functions in the body. The liquid in the plasma keeps these cells in a consistent suspension.

One empty and one full pint-sized blood bag.
One empty and one full pint-sized blood bag.

In addition to cells, blood also contains hormones, lipids, amino acids, dissolved gases, waste materials from cells, proteins, electrolytes, carbohydrates, and vitamins. This complex chemical stew delivers nutrients and gases to cells in the body so that they can function and exchanges these materials for wastes which the cells need to eliminate so that these wastes can be carried away. Blood cycles continually through the body, delivering materials and carrying others away.

A pouch of AB- blood.
A pouch of AB- blood.

The composition of the blood is constantly changing and the body uses a variety of systems to regulate it. Nutrients, for example, are taken in from the intestinal tract. The kidneys filter the blood to remove cellular wastes and to balance the levels of certain chemicals in the blood so that they stay consistent. At the lungs, blood is involved in a gas exchange where carbon dioxide is released and oxygen is taken up by the blood.

Blood plasma.
Blood plasma.

When people are sick, their blood composition can change. For example, if someone has a malfunctioning endocrine gland, the levels of hormones in the blood may be unusually high or low because the gland is not producing them in the right amount. A blood test can reveal the imbalance, providing a doctor with a tool for determining what is wrong with the patient. Likewise, when people become dehydrated, the levels of electrolytes in their blood become skewed, which can lead to cell damage.

For a blood test, blood is drawn from the body so that the blood composition can be analyzed. It is allowed to sit or spun in a centrifuge so that the plasma and cells separate to facilitate testing.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a WiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a WiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

Discussion Comments

OShiva

White blood cells also increase when someone is sick. White blood cells can be considered "doctor cells". When there is a problem, more cells are produced to help fight and contain whatever foreign matter there is. Sometimes, elevated white blood cell counts are the first indicator of a health problem.

Post your comments
Login:
Forgot password?
Register:
    • One empty and one full pint-sized blood bag.
      By: .shock
      One empty and one full pint-sized blood bag.
    • A pouch of AB- blood.
      By: Africa Studio
      A pouch of AB- blood.
    • Blood plasma.
      By: dazzi-b
      Blood plasma.
    • Erythrocytes are red blood cells that carry oxygen to different areas of the body.
      By: Monika 3 Steps Ahead
      Erythrocytes are red blood cells that carry oxygen to different areas of the body.