Ready to donate?

You can make and manage your appointments online

Make appointment now


You can call us on

13 14 95

Explainer: what’s actually in our blood?

Friday 12th Jan 2018

Blood is vitally important for our body. As it’s pumped around our body through veins and arteries, it transports oxygen from our lungs to all of the other organs, tissues and cells that need it. Blood also removes waste products from our organs and tissues, taking them to the liver and kidneys, where they’re removed from the body.

About 45% of our blood consists of different types of cells and the other 55% is plasma, a pale yellow fluid. Blood transports nutrients, hormones, proteins, vitamins and minerals around our body, suspended in the plasma. They provide energy to our cells and also signal for growth and tissue repair. The average adult has about five litres of blood.

The different types of blood cells include red blood cells, platelets, and white blood cells, and these are produced in the bone marrow, in the centre of our bones.


The Conversation, CC BY-ND

Red blood cells

Red blood cells are essential for transporting oxygen around the body. Red cells are very small, donut-shaped cells with an average lifespan of 120 days within the body. They contain a protein called haemoglobin, which contains iron and binds very strongly to oxygen, giving blood its red colour.

Red cells are flexible and able to squeeze through even the tiniest of our blood vessels, called capillaries, to deliver oxygen to all of the cells in our body. When the red cells reach our organs and tissues, haemoglobin releases the oxygen.


Platelets are even smaller than red blood cells. In fact, they are tiny fragments of another much larger type of cell, called a megakaryocyte, which is located in the bone marrow. Platelets are formed by budding off from the megakaryocyte. Platelets have an average lifespan of eight to 10 days within the body, so they are constantly being produced. When body tissue is damaged, chemicals are released that attract platelets.

Platelets clump together and stick to the damaged tissue, which starts to form a clot to stop bleeding. Many of the proteins that help the clot to form are contained in plasma. Platelets also release growth factors that help with tissue healing.

White blood cells

Blood also carries white blood cells, which are an essential part of our immune system. Some white cells are able to kill micro-organisms by engulfing and ingesting them. Other types of white cells, called lymphocytes, release antibodies that help to fight infection.

Blood cells don’t act alone; they work together for normal body function. For example, when we cut our skin, platelets help plug the cut to stop it bleeding, plasma delivers nutrients and clotting proteins, white cells help to prevent the cut from becoming infected, and red cells deliver oxygen to help keep the skin tissue healthy.

Blood transfusions

Sometimes patients who are having surgery, cancer treatment or when they are seriously injured need a blood transfusion. This is usually because they have lost a lot of platelets, red cells or plasma, or because their cancer treatment has killed many of their blood cells.

The journey of blood.

In Australia, blood is donated by voluntary blood donors at the Australian Red Cross Lifeblood. A typical whole blood donation is just over 450 mL, and it takes around ten minutes to collect. Every time a donation is made, the donor is screened for infectious diseases such as hepatitis and HIV, so these aren’t transferred to the patient receiving the blood.

After donation, the blood is separated into its different parts: platelets, red cells and plasma, which are known as blood components. White cells are removed because they can cause problems in patients who receive them. Once the blood has been separated, it’s stored until it’s needed by hospitals. The red blood cells are stored in a refrigerator and the plasma is frozen. The red cells can be stored for six weeks, and the plasma can be stored for up to a year. Platelets can only be stored for five days. When a hospital needs blood it’s packed into special blood shippers, and transported to the hospital blood bank to be transfused.


A/Prof Denese Marks

Adjunct Associate Professor, University of Sydney

National R&D Leader - Product Development and Storage at Australian Red Cross Lifeblood. Dr Marks’ research focuses on all aspects of improving blood component quality and safety from blood collection through to processing, storage and transfusion. This includes development of novel blood products such as platelet lysate and frozen blood components. Dr Marks has published over 50 peer reviewed papers.


I have and still receiving some chemo treatment for leukemia and during part of the treatment I received blood products to help with the keeping my blood counts you probably know some chemo is pretty toxic in the scale of it all so just wanted to say thank you and to people donating blood through these tough times and my blood type is A+ so every one A+ a big thank you.

Thanks James for sharing your story with us. We're glad to be able to support you through your treatment with the help of our generous donors, and hope you're feeling better soon.

Soo generous of you to donate their blood and plasma to other people who need it

nice process. its very good to enhance knowledge and to share with the other volunteers

Useful. Well understood.


So much of technology and development happens is it possible to create or manufacture blood....?

Thanks Ashwin-that's really good question. I think I'll leave the detailed answer for another blog post. The short answer is: although it is now technically possible to grow blood cells from stem cells in a laboratory, the process is still very expensive, and can't yet be done at the scale we need. We will be relying on our real live human volunteers for the foreseeable future.

the blood component,safety and donation information is very important especially to african society

Depending on the person, there are usually between 4.2 and 6.1 MILLION cells in every microlitre (that's a very small drop) of blood. If we take a mid-range value of 5 million red cells per microlitre, that works out to a grand total of 2.25 TRILLION (or 2.5 million, million) red cells in 450 mL.

Hello Dear, I appreciate your effort to teach us. I like this topics and I have got new update knowledge. Sincerely, Melaku

how many red blood cells in an average of 450ml

Add new comment

The information on this blog is presented by the Lifeblood’s Research and Development Team for the purposes of sharing general information and facilitating discussion about blood donation. It is not intended to be used or relied upon as medical advice. If you have a medical question, please consult your GP or health professional. For information on blood donation, or to find out if you’re eligible to donate, call 13 14 95.