7. Epilogue: the future of blood

For a long time, synthetic biologists have attempted to manufacture an artificial, easily stored and transported, blood substitute that does not require blood typing, is long lasting, and can be guaranteed pathogen free. Three different methods have been attempted to replace red blood cell transfusions: the use of perfluorocarbons, inert chemicals that, in liquid form, can dissolve gases without reacting with them; creating a haemoglobin-based blood substitute—but despite almost a billion dollars of research and development there is not one in general use today; and growing artificial red blood cells using stem cell technology—but doing this safely, reproducibly, and in large amounts is a huge bioengineering challenge.

6. Blood transfusion

‘Blood transfusion’ outlines the history of transfusing animal blood dating back to the 17th century. The 19th century saw the first successful human blood transfusion, but two major issues remained: the problems of clotting and blood group incompatibility. Albert Hustin and Luis Agote resolved the first issue in 1914 by using sodium citrate in transfusions to work as an anticoagulant. Richard Lewisohn calculated the correct levels of citrate needed to avoid poisoning the blood. Karl Landsteiner’s work in early 20th-century Vienna revealed the ABO blood type distinctions, solving the latter problem. The creation of blood banks and the potential for viral contamination of blood and blood products are also discussed.

4. Haemoglobin

‘Haemoglobin’ explains the key role played by this protein: binding oxygen in the lungs and carrying it around the blood circulation, where it is offloaded to every cell in the body. Haemoglobin has also played a key role in the history of our understanding of all proteins and the science of biochemistry. The complex, three-dimensional quaternary structure of haemoglobin was identified in 1960 by Max Perutz. A haemoglobin tetramer contains four haem groups and can bind four molecules of oxygen. Chemical interaction of oxygen with haem iron is explained along with diseases—such as sickle cell disease, thalassaemias, and haemoglobinopathies—caused by changes in the globin part of the protein.

3. Fighting disease

‘Fighting disease’ looks at how the immune system and vaccination work. It considers the scientific studies of Louis Pasteur, late in the 19th century, who brilliantly expanded on the work of Robert Koch and Friedrich Henle, to formally expound the germ theory of human disease. But how did the body defend itself against these micro invaders? The phagocytic theory of immune defence resulted from the work of Élie Metchnikoff, Paul Ehrlich, and Emil von Behring. Immunoglobulin molecules provide the key to how the body creates the variety of molecules needed to protect against the different invaders experienced over a lifetime, and to how vaccination against a disease protects against future infection.

1. A history of blood

‘A history of blood’ considers why the colour red and blood hold such pre-eminence in human language and culture. Views about what function blood actually performed in the body have varied widely through history. The studies of 2nd-century physician Galen are described along with procedures such as bloodletting, used in medicine for a long time. The structure of the vessels that contain blood in the body—arteries and veins—has always intrigued scholars. The 13th-century Islamic physician Ibn al-Nafis was the first to propose a circulatory system, but it was in 1628, when William Harvey, physician to King James I, published his findings, that the true circulatory system was explained.

5. Blood pressure and blood flow

The heart is the organ that pumps blood around the body. If the heart stops functioning, blood does not flow. The driving force for this flow is the pressure difference between the arterial blood leaving the heart and the returning venous blood. ‘Blood pressure and blood flow’ first considers how blood pressure is measured and how blood pressure can affect health. High blood pressure is called hypertension and low blood pressure hypotension. Chronic hypertension has serious long-term adverse health consequences, but can be treated with improved lifestyle choices and a range of medicines, including anti-hypertensive drugs, beta blockers, and ACE inhibitor drugs. The different molecules affecting blood flow are also considered.

2. What is blood?

‘What is blood?’ describes the constituent parts of blood: a fluid called plasma in which three different cell types are carried—red cells, white cells, and platelets. Red cells are dominated by the red protein haemoglobin that plays the key role in transporting oxygen from the lungs to the tissue. A lack of red blood cells is called anaemia. A lack of iron is the main cause, iron being required to make a functional haemoglobin protein. White cells, or leucocytes, perform many and varied roles in the body, but all are related to immune defence against pathogens. Platelets have only one function: the prevention of excess bleeding through coagulation.