Blood is one of the most important body fluids. It is a mixture of various components and each has a special and important role to play in the body. A problem in any of the components of the blood may result in serious medical conditions.

What does blood do to the body?

It is involved in various bodily processes such as:

  • Carrying nutrients and oxygen in various parts of the body, especially to the lungs.
  • Play a major role in bleeding as it promotes blood clot thereby preventing excessive blood loss.
  • Helps get rid of infection by carrying cells and antibodies to the infection site.
  • Facilitates waste elimination by filtering the blood and excrete the waste materials from the kidneys and liver.
  • It plays a vital role in thermoregulation. (1, 2, and 3)

Whole Blood

This is the kind of blood that runs through various parts of the body. Whole blood consists of plasma (55%) and blood cells (45%). Don’t you know that about 8% of the total body weight is composed of blood? That accounts to about 12 pints of blood in an average man’s body. Women have only nine pints of blood. (3, 4)

Blood Cells

These are cells produced during hematopoiesis; a process of making blood. Blood cells developed from hematopoietic stem cells. They are formed in the bone marrow through the process of hematopoiesis and the hematopoietic stem cells have the ability to transform into blood cells; specifically red blood cells, white blood cells, and platelets.

Stem cells are present in people of all ages, especially located in the blood, bone marrow, and umbilical cords of newborn babies. The very same stem cells are used to treat and manage immune-related disorders, leukemia, and bone marrow failure. (4, 5)

Four types of blood cells and their functions

Red blood cells when viewed under the microscope

Image 1: Red blood cells when viewed under the microscope.

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#1 – Red Blood Cells/Erythrocytes

What is RBC? The red blood cell is the most abundant blood cell in the body (about 45%). Under microscopic examination, red blood cells are a biconcave disk in shape and have a flattened center. They look like a donut. The production of red blood cells is dependent on the release of the hormone erythropoietin, which is primarily produced by the kidneys.

Red blood cells begin as immature cells in the bone marrow. It would require about seven days for red blood cells to mature and be released into the bloodstream. The average lifespan of a red blood cell is 120 days. Therefore, it is important for the body to continuously produce red blood cells.

An essential component of red blood cell is hemoglobin; a substance that carries oxygen from the lungs to various parts of the body and vice versa in the form of carbon dioxide going back to the lungs for reoxygenation. Hemoglobin has a red color, which accounts to the color of the blood primarily because most of the blood cell component is made up of red blood cells. Haematocrit is a parameter that measures the level of red blood cell. (4, 5, and 6)

What to keep in mind?

  • They are a donut-like structure under the microscope.
  • They usually live for 120 days and then die.
  • They contain hemoglobin which is responsible for the blood’s red color.

#2 – White Blood Cells/Leukocytes

White blood cells in a blood smear

Image 2: White blood cells in a blood smear.

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This type of blood cell is also known as the fighter cell. It is primarily involved in fighting off infection. It accounts for only 1% of the total blood volume. There are different types of white blood cells. What are the five types of WBC and their functions?

  • Neutrophil – It is the immediate response cell which accounts to about 70% of the total white blood cell count. Neutrophil’s life span is less than a day. The bone marrow needs to produce neutrophils on a day to day basis to up the body’s response against infection.
  • Lymphocyte – This type of white blood cell is divided into two: T lymphocyte and B lymphocyte.
    • T lymphocytes – They regulate the functions of immune cells. They are fighter cells because they attack infected cells and tumors.
    • B lymphocytes – They make antibodies that target foreign substances like viruses, bacteria, and other foreign antibodies.
  • Eosinophils/Granulocytes – They are responsible for killing parasites. They also play a vital role in the allergic response. They kill pathogens by releasing toxins from their granules.
  • Basophils – They secrete antibodies and anticoagulants which are responsible for fighting hypersensitivity reactions in the bloodstream. They contain histamine responsible for dilating the blood vessels thereby enabling more immune cells to the injured site. They also secrete heparin, an anticoagulant that promotes white blood cell mobility thereby preventing a blood clot.
  • Monocytes/Agranulocytes – They are the largest type of white blood cell characterized by their kidney-shaped nucleus. They can last for a few hours to days. They destroy damaged and old cells by turning into macrophages once they enter into the bloodstream. (4, 5, 6, and 7)

What to keep in mind?

  • They composed approximately 1% of the total blood volume.
  • The number of white blood cells rises in the presence of infection.
  • Inappropriate production of white blood cells leads to haematological cancer.

#3 – Platelets/Thrombocytes

microscopic examination of platelets

Image 3: A microscopic examination of platelets.

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They are not actually cells but a small fragment of cells. Although they are small, they play a huge role in the circulatory system. They are responsible for blood clotting process/coagulation. If there is a wound, platelet goes to the injury site and stick to the lining of the injured vessels. Blood coagulation occurs resulting in the formation of fibrin clot thereby preventing further blood loss.

Platelets should be at a normal level at all times. Too much platelet leads to unnecessary clotting leading to stroke and heart attack. On the other hand, too little platelet can lead to extensive bleeding. Aside from the blood clotting factor, platelets also digest and destroy bacteria. (7, 8, and 9)

What to keep in mind?

  • The average lifespan of a platelet is between five to nine days.
  • Too low platelet leads to excessive bleeding.
  • Too high platelet leads to thrombosis which may result in stroke.

#4 – Plasma

liquid yellowish component of the blood

Image 4: It is the liquid yellowish component of the blood

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It is the fluid component of the blood consists of different components namely: a mixture of water, salt, protein, sugar, and fat. The primary role of plasma is to transport blood cells throughout the different parts of the body.

Aside from blood cells, it also carries other important components like hormones, antibodies, clotting proteins, nutrients, proteins, and even waste products. (5, 7, 8, 9, and 10)

What to keep in mind?

  • It is a fluid yellowish in color.
  • It carries cells and proteins.
  • It consists of 55% of the total blood volume.

What are the types of blood groups?

  1. Blood Group A – It has A antigen (RBCs) and B antibody (plasma).
  2. Blood Group B – It has B antigen (RBCs) and A antibody (plasma).
  3. Blood Group AB – It has both A and B antigens (RBCs) and none in the plasma.
  4. Blood Group O – It does not have A and B antigens (RBCs) but has both A and B antibodies (plasma.) (11)



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