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Blood Components

11 Apr 2024

Tags: Haematology | Medical Emergencies

Blood Components Introduction

Blood plays a vital role in the body’s functioning as it circulates through the vascular system. Its functions include the transportation of oxygen and nutrients to tissues, the removal of waste products to the liver, assistance in regulating body temperature, and serving as a reservoir and conduit for immune cells. Additionally, blood possesses the capability to form clots, thereby halting excessive blood loss during injuries.

An average human adult typically has over five Liters of blood, constituting approximately 7-8% of their body weight.

Our blood is made up of four components:

Red blood cells

White blood cells



Rhabdomyolysis Urine

Red Blood Cells (RBCs)

Red blood cells, or erythrocytes, are perhaps the most recognizable component of blood due to their vibrant colour and abundance. These specialised cells are primarily responsible for transporting oxygen from the lungs to tissues and organs throughout the body, facilitated by the protein haemoglobin.

Structurally, RBCs lack a nucleus and most organelles (do not contain DNA), maximising their capacity to carry oxygen. They are biconcave in shape and makeup around 40-45% of blood volume.

The lifespan of a red blood cell is approximately 120 days before they are removed by the spleen and liver, and their continuous production in the bone marrow ensures the body’s oxygen needs are met.

Red Blood Cells (WBCs)

White Blood Cells (WBCs)

White blood cells, also known as leukocytes, are the immune system’s frontline defenders, tasked with identifying and neutralizing foreign invaders such as bacteria, viruses, and other pathogens.

Unlike red blood cells, white blood cells possess a nucleus and are classified into several subtypes, including neutrophils, lymphocytes, monocytes, eosinophils, and basophils, each with distinct roles in immune response.


Neutrophils are the most abundant type of white blood cell and play a crucial role in the body’s defence against bacterial infections by engulfing and destroying pathogens.


Lymphocytes are a diverse group of white blood cells that contribute to the body’s immune response by producing antibodies to target specific pathogens and coordinating the immune system’s actions.


Eosinophils are white blood cells involved in combating parasitic infections and regulating allergic reactions by releasing chemicals that help to neutralize invading organisms and reduce inflammation.


Basophils are a type of white blood cell that releases histamine and other chemicals involved in allergic responses, inflammation, and combating certain parasites, playing a role in the body’s immune and inflammatory responses.

White Blood Cells (WBCs)


Platelets, or thrombocytes, are small, disk-shaped cell fragments essential for blood clotting and haemostasis. When a blood vessel is injured, platelets quickly adhere to the site of damage, forming a temporary plug to prevent excessive bleeding. Platelets also release various growth factors and cytokines that promote tissue repair and regeneration, highlighting their role in wound healing and vascular integrity.



Plasma, the liquid component of blood, constitutes the largest portion of blood volume and serves as a medium for transporting nutrients, hormones, waste products, and other essential molecules throughout the body. Makes up around 55-60% of blood by volume.

Composed mainly of water, plasma also contains a diverse array of proteins, including albumin, globulins, and fibrinogen, as well as electrolytes, gases, and metabolites.


Key Points

  • Blood consists of red blood cells, white blood cells, platelets, and plasma, each serving vital functions.

  • Red cells carry oxygen, white cells defend against infections, platelets aid clotting, and plasma transports nutrients and waste.

  • Maintaining balance in blood components is crucial for overall health and preventing disorders.


Blood components. (n.d.). NHS Blood Donation. https://www.blood.co.uk/why-give-blood/how-blood-is-used/blood-components

Dean, L. (2005). Blood and the cells it contain. National Library of Medicine; National Center for Biotechnology Information (US). https://www.ncbi.nlm.nih.gov/books/NBK2263