Overview of Blood Components


What Is Blood?

A fluid called blood circulates through the vessels of the circulatory system. Human blood consists of platelets, fragments of blood cells, plasma (the liquid component), and blood cells (red and white).

The primary component of blood, plasma, primarily consists of water with small amounts of proteins, nutrients, ions, and wastes.

The transport of carbon dioxide and oxygen is carried out by red blood cells.

Platelets cause blood clotting.

White blood cells play a role in immune response and are a component of the immune system.

In human blood, plasma makes up 55% of the volume and cells and platelets constitute about 45%.

The bone marrow produces blood cells. The spongy substance that fills the middle of the bones and produces all different kinds of blood cells is called bone marrow.

Components of Blood

Human blood components are as follows:

  • Plasma is the liquid part of the blood and contains the blood cells listed below:
  • Blood cells, red (erythrocytes) distribute oxygen throughout the body from the lungs.
  • White blood cells (leukocytes) support the immune system and contribute to the defence against infections. White blood cells are of the following types:
  • Lymphocytes
  • Monocytes
  • Eosinophils
  • Basophils
  • Neutrophils
  • Platelets (thrombocytes) facilitate blood clotting (or coagulation).


The liquid component of blood is referred to as plasma or blood plasma. Plasma acts as a carrier for the transportation of nutrients to the cells of the organs and waste products from cellular metabolism to the liver, kidneys, and lungs for elimination.

The plasma comprises 10% ions, nutrients, proteins, wastes, and dissolved gases and contains 90% water. The primary protein in human plasma, albumin, plays a significant role in maintaining blood pH and osmotic equilibrium among other proteins, ions, and other compounds.

White Blood Cells

White blood cells (WBCs), also referred to as leukocytes, are essential for protecting the body from infection. The two primary categories of WBCs are the granulocytes, including the eosinophils, neutrophils, and basophils, and the agranulocytes, comprising the lymphocytes and monocytes.

White blood cells play a very different function than red blood cells, primarily contributing to the immune response to recognise and attack pathogens, including invasive viruses, bacteria, and foreign species.

Granular inclusions in the cytoplasm and a lobed nucleus are characteristics of granulocytes, which include neutrophils, eosinophils, and basophils. During injury or infection, granulocytes are usually the first to respond.

The primary immune system cells are lymphocytes, which comprise B cells, T cells, and natural killer cells. B cells eliminate bacteria and neutralise their poisons. Additionally, they produce antibodies. T cells target cancer cells, transplanted cells, certain bacteria, fungi, and viruses. Toxins are released by T cells as they target viruses, killing them. Natural killer cells target many pathogenic microorganisms as well as specific tumour cells.

Red Blood Cells

Erythrocytes, also known as red blood cells, are specialised cells that circulate throughout the body supplying oxygen to cells; they are produced in the bone marrow from stem cells.

Haemoglobin, a protein that contains iron, gives blood its red colour. The primary function of haemoglobin is to transport oxygen, sometimes carbon dioxide.

Mature red blood cells in humans are biconcave, flexible discs. RBCs lack a cell nucleus, as well as organelles, to facilitate maximum area for haemoglobin.

Human tissues use oxygen to produce energy and emit carbon dioxide as waste. The red blood cells in our body are responsible for transferring oxygen from the lungs to the tissues of the body. The red blood cells transport the waste carbon dioxide to the lungs so that we can exhale it.

Platelets and Coagulation

The cell fragments known as platelets, or thrombocytes, are essential for blood coagulation. They are produced when giant cells called megakaryocytes separate, making 2000–3000 platelets every time.

The purpose of platelets is to arrest bleeding. Our platelets will congregate during an accident to form a plug at the site of the wound that seals blood arteries through a process known as clotting or coagulation to stop extra blood from leaving the body.

The process through which blood transforms from a liquid to a gel and forms a blood clot is known as coagulation, often known as clotting. It may lead to hemostasis, the stopping of blood loss from an injured vessel, accompanied by its repair. The coagulation process includes the activation, adhesion, platelet aggregation, and accumulation and maturation of fibrin.

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