Blood

A guide to the human blood system and alternatives

Human blood

Blood is a vital fluid for humans and vertebrates. It transports nutrients, including oxygen, to cells and tissues. Blood is made of different components: red blood cells, white blood cells, platelets and plasma.

Red blood cells (also called erythrocytes) contain haemoglobin, which gives blood its red colour. Haemoglobin helps to carry oxygen to the body from the lungs.

White blood cells (also called leukocytes) defend the body against infections.

Lymphocytes are a type of white blood cell, and the two types are T lymphocytes and B lymphocytes. T lymphocytes target infected cells and regulate the function of other immune cells. B lymphocytes, on the other hand, create antibodies, which are proteins that can destroy foreign substances like bacteria and viruses.

Platelets (also called thrombocytes) are small cell fragments. They are essential in blood clotting, a process known as coagulation. Platelets also help wounds heal and contribute to the immune response.

Plasma is the liquid component in blood, made of water, ions, proteins, nutrients, wastes and gases. Its main role is transporting substances such as blood cells and other nutrients throughout the body.

Artificial blood

There are two main types of artificial blood: haemoglobin-based oxygen carriers (HBOCs) and perfluorocarbons (PFCs).

HBOCs are synthetic solutions designed to carry oxygen. They are usually a smaller size than RBCs. The haemoglobin is modified and covered with carriers to ensure the HBOCs do not break down inside the body. They can be used for blood transfusions that need to be done immediately or when there is too much blood loss.

PFCs are derived from fluorine-containing and carbon-containing chemicals, and have a high capacity for carrying and delivering oxygen.

Advantages and disadvantages of artificial blood

Artificial blood can be beneficial because it can be used for any patient who needs a blood transfusion, regardless of their blood type, if the substitute has the universal O blood group. There is also less chance of diseases being passed to patients using artificial blood.

However, artificial blood has been shown to have adverse side effects, including high blood pressure and a higher chance of heart attacks.

The future of artificial blood

There have been experiments in the NHS with laboratory-grown RBCs in the RESTORE randomised controlled clinical trial, which aims to see if RBCs produced from stem cells in a lab can survive longer in the body than normal donated cells. As part of the trial, scientists created lab-grown RBCs to be given to healthy volunteer participants in small doses. In February 2026, the final batch of RBCs produced as part of the trial was given to volunteers. This trial highlights the potential for artificial blood to be used in clinical settings, especially when supply is low or for patients with rare blood types, diseases, or complex transfusion requirements. The results of this trial are planned to be shared in late 2026 or early 2027.

Written by Naoshin Haque

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