All About Blood

September 6, 2022
by Hannah Farrell

What does blood do?

Our blood has several functions:

  • To transport oxygen and nutrients around the body.
  • To transport waste products from tissues to the lungs, kidneys, and liver to be metabolised and excreted from the body.
  • To transport hormones around the body.
  • To protect the body by carrying immune cells and antibodies which fight infection.
  • To protect the body from excessive bleeding by providing blood clotting factors.
  • To regulate the body’s temperature by absorbing heat and controlling the flow of blood throughout the body through vasodilation and vasoconstriction.
  • To regulate the body’s pH level.

Blood travels through our body through a complex system of arteries, veins, and capillaries. Further reading on the human vascular system can be read here.

What are the components of blood?

Red blood cells (erythrocytes): contain haemoglobin which binds to oxygen and allows it to be transported to tissues around the body.

White blood cells (leukocytes): responsible for the immune response, cells such as neutrophils, eosinophils, and leukocytes help to protect the body from infection.

Platelets (thrombocytes): cell fragments which stick together and form a blood clot.

Plasma: a straw-coloured fluid which the white and red blood cells are suspended in, allowing movement. Plasma also acts as a solute which transports:

  • Albumin: a water-soluble protein which prevents fluid from leaking out of blood vessels and into surrounding tissues.
  • Fibrinogen (Factor I): a protein which can be converted to fibrin, which forms a blood clot.
  • Gamma globulins (antibodies): proteins responsible for the immune response.
  • Factor VIII (anti-haemophilic factor): protein essential for blood clotting.
  • Salts, sugars, fats, hormones, and vitamins.

Where is blood produced?

The majority of blood cells are produced in the bone marrow, found mostly in the pelvis, spine, and sternum. Blood cells develop from stem cells and use growth factors to mature into the specific types of blood cell i.e., thrombocyte, leukocytes, erythrocytes etc. Before maturing into specific blood cell types, the stem cells develop into two types of progenitor cells; myeloid and lymphoid.

Myeloid stem cells mature into:

  • Red blood cells (erythrocytes)
  • Neutrophils
  • Eosinophils
  • Basophils
  • Monocytes
  • Platelets

Lymphoid stem cells mature into:

  • T cells
  • B cells

Red blood cell production (erythropoiesis) is controlled by erythropoietin (EPO), a hormone produced in the kidneys. Individuals suffering from renal failure can present with anaemia due to the reduced levels of EPO and therefore reduced levels of erythropoiesis.

The majority of white blood cells are produced in the bone marrow. Lymphocytes (T & B cells) are also produced in the spleen and lymph nodes, with T cells also being produced and maturing in the thymus gland.

Our Medico-Legal Expert Witnesses in Haematology are able to provide expert advice on all things related to the blood, including blood transfusions and what can go wrong.