What is in blood and where is it made?

What is in blood and where is it made?

Components of blood

Blood is a complex, dynamic mixture of cells, proteins, ions, sugars, signalling molecules, nutrients and gases suspended or dissolved in water. Blood also re-distributes heat. The composition of blood constantly varies in response to our diet, exercise status, hydration, time of the day, injury and challenges from pathogens. As well as its fundamental role in mammals, blood products have important ex-vivo applications. For example, serum and albumin are important reagents that enable cell culture.  How is blood made? What are the components of blood? Where do these components of blood come from?

See also related article: Sera and Plasma: Do you know the difference?



Composition of blood. Examples of some of the main components of blood. Blood's appearance following the addition of anti-coagulant and centrifugation is shown on the left.  The straw-coloured plasma sits above the red cells separated by a layer of white cells known as the buffy coat. Components are arranged roughly in order of size ranging from cells to small molecules including water. For the antibody and smaller molecules, space-filling molecular structures are used. For a further description of the components, see the table below. IMAGE credit: Cell Guidance Systems and Bigstock (Lipoproteins and EPO graphics).  


Blood is made in many different organs

As blood travels around the body, various organs and tissues along its route contribute to the production of its components. Some of these tissues and organs, such as bone marrow,  are primarily focused on producing blood components, whereas others, such as the liver, have many other important functions.  As well as carrying nutrition, oxygen and cells of the immune system, the blood carries signalling molecules around the body such as hormones, cytokines and RNA. Signalling molecules may be carried in extracellular vesicles such as exosomes. These small hollow spheres of lipids and proteins fuse efficiently with target cells to release their bioactive components. The blood also carries waste products from tissues to organs of the body, such as the liver, lungs and kidneys that filter and secrete them.  All these components have different lifespans and mechanisms for removal from the blood. The table below focuses on their function and origin. Components are listed in approximate order of their size. 


Table. The key components of blood, their function and source 






Required for metabolism

Air via the lungs
Carbon Dioxide

A waste product of metabolism

All cells and air via the lungs

Component of other molecules

Air via the lungs
Nitrous oxide

A vasodilator

All cells



A fluid carrier for other components of the blood and a source of hydration for cells in the body.    

Ingested and absorbed through the digestive system. 

Small Molecules


Maintaining osmolarity, source of ions for cellular function. When overall salt levels are too high, this is sensed by the brain making us thirsty

Ingested and absorbed through the digestive system. 

Waste products from cells are transported in the blood for removal, principally by the kidneys and the liver. 

All cells

Source of energy

Ingested and absorbed through the digestive system. 
Vitamins and nutrients

Required for cellular function and metabolism 

Ingested and absorbed through the digestive system. Skin (vitamin D)


Signalling Molecules

Cytokines and growth factors.  Small protein messenger molecules. Please see this article for further details.   They are generated by all cells.

Messenger molecules can be proteins, such as insulin, or chemicals, such as thyroxin.  Examples of hormones include:

Secreted from a variety of sources

The development of female sex organs regulates the menstrual cycle. 


Development of male sex organs, musculature, and facial hair. 

Made mainly in testes but other origins (e.g. ovaries)

Regulates blood sure levels. 


Regulates blood sure levels. 


Assists in blood pressure control. 


A precursor to triiodothyronine. 


Controls metabolic rate.

Liver, kidneys and others

Block pain. 

Anterior pituitary
Anti-diuretic hormone  

Stimulates water retention by the kidneys. 

Made in the hypothalamus, secreted by the pituitary

Major Blood Proteins


Serum Albumin is the major protein in plasma. Albumin binds to and transports hormones, fatty acids, and other compounds. Albumin buffers pH, and maintains oncotic pressure, among other functions. 

Made in the liver

Produced in millions of different forms to recognize foreign proteins. 

Produced by B cells (see below) with help from T cells).

An insoluble protein arranged in long chains. Enables clotting. 

Formed by the action of thrombin on fibrinogen.

A glycoprotein complex that is converted to fibrin during injury. 

Made in the liver 

Haemoglobin binds to oxygen to transport it from the lungs to other tissues in the body. Haemoglobin also transports about 75% of the carbon dioxide in the blood for exhalation. Haemoglobin is packaged in red blood cells to prevent it from wreaking oxidative havoc in the vasculature and exposed tissues. 

Red bone marrow

Lipids (Fats)


Important for building cell walls, making hormones, bile acids and vitamin D. Dangerous in excess contributing to heart disease.  Can be combined with proteins into Lipoproteins (See below)

Made in the liver and also absorbed from foods via the digestive system

Provide a stored source of energy between meals. Can be combined with proteins into Lipoproteins (See below)

Provided by foods, fat cells and made in the liver. 


(complexes of lipids and proteins)  

Chylomicrons – the largest lipoprotein 

Carry triglycerides from the intestine.

Very low-density lipoproteins (VLDL)

Transport triglycerides made in the liver.


Low-density lipoproteins (LDL)

transport cholesterol made in the liver. This cholesterol is LDL-cholesterol. It is generally considered to be bad cholesterol.

High-density lipoprotein (HDL)

Removes excess cholesterol away from artery walls and cells back to the liver for recycling and disposal. Generally considered good.

Artery walls

Extracelular Vesicles

Extracellular vesicles (EVs)

Small hollow spheres of varying size with lipid walls containing protein and RNA cargo. Includes exosomes (50-200nm), microparticles (200 nm to 1 µm) generated by viable cells and apoptotic bodies generated by dying cells. Exosomes provide messenger function and are present at about 1x1012 per ml. 

Generated by all cells.



Small, disc-shaped fragments that help to form clots in injured tissue. These are formed from the cytoplasm of megakaryocytes. They are found at a ratio of about 1 per 20 red blood cells and have a lifespan of 7-10 days.

Megakaryocyte cells are found in bone marrow and lung

Red Blood Cells

Red blood cells

Make up about 40% of total blood volume. Their primary role is to provide a package for haemoglobin.

Red bone marrow




White Blood Cells

White Blood cells (leukocytes)

Present at a ratio of 1 white blood cell for every 600-700 red blood cells. Fight of infection and help to remodel damaged tissue. White blood cells are also called leukocytes

Bone marrow, thymus

A type of white blood cell, further divided into individual cell types 

Bone marrow, thymus
T cells.

Fight infection and diseases such as cancer. 

Natural Killer cells.

Part of the innate immune system provides an initial response to infection by attacking virus-infected cells. 

Bone marrow
B cells. 

Adaptive immune cells produce antibodies against pathogens. 

Bone marrow

Most prevalent lymphocytes account for about 50% of the total. Phagocytic cells that ingest pathogens.

Bone marrow

Phagocytic cells that ingest pathogens. Move from blood into inflamed tissue where they differentiate into macrophages which can orchestrate immune response and tissue remodelling. 

Bone marrow

Kill parasites, destroy cancer cells, and are involved in allergic responses. 

Bone marrow

Participate in allergic responses

Bone marrow

Probably wrong to classify them as white blood cells as they are not primarily found in the blood. Macrophages are phagocytic cells that can originate in the tissues where they are found (tissue-resident macrophages) and also differentiate from monocytes after they have extravasated from the blood through the blood capillary walls into tissues.

Bone marrow and other tissues


Top IMAGE: Bigstock

Copyright Cell Guidance Systems

Learn more about powerful technologies that are enabling research: