50 Fun Facts About Blood

Roughly what percentage of an adult human's body weight is blood?

7% is the textbook figure: blood accounts for roughly 7 to 8 per cent of adult body weight, and its density is only slightly greater than water's.

Roughly how much blood does the average adult have?

About 5 litres of blood circulate in a typical adult; women average a little less than men, and the volume rises markedly during pregnancy.

What is the straw-yellow liquid that makes up about 55% of blood?

Plasma is the straw-coloured fluid fraction of blood; serum is the name for plasma with the clotting proteins removed, and both are mostly water.

Which iron-containing protein in red blood cells carries oxygen?

Hemoglobin is a globin protein carrying iron-containing haem groups; it gives red cells their colour and makes up roughly a third of each cell's weight.

How many oxygen molecules can a single molecule of the red cells' oxygen-carrying protein bind?

4 is the maximum: each of the protein's four haem groups binds one oxygen molecule, and the reversible, cooperative binding is what makes transport efficient.

Roughly how long does a human red blood cell circulate before it is recycled?

100-120 days is the typical lifespan; worn-out red cells are broken down by macrophages, mainly in the spleen, and their iron is recycled for new cells.

Unlike those of birds, reptiles and fish, mature mammalian red blood cells lack what?

A nucleus is shed as mammalian red cells mature, leaving a flexible biconcave disc; birds, reptiles and fish keep oval, nucleated red cells throughout life.

What is the term for the proportion of blood volume occupied by red blood cells, normally about 45%?

Hematocrit, also called packed cell volume, is read by spinning a sample in a centrifuge; values run higher in men than in women and rise at high altitude.

Platelets are not true cells but fragments of the cytoplasm of which large bone-marrow cells?

Megakaryocytes, giant polyploid cells in the marrow, each shed thousands of platelets from their cytoplasm; the resulting anucleate fragments are unique to mammals.

Human blood pH is tightly regulated within which narrow range?

7.35 to 7.45 is the normal arterial range, held by bicarbonate buffering, with the lungs adjusting carbon dioxide and the kidneys excreting acid or base.

Approximately how many blood cells does human bone marrow produce every day?

500 billion blood cells a day is the usual estimate, roughly 2 million red cells every second, released into the circulation through the marrow's permeable sinusoids.

Which Austrian physician discovered the ABO blood groups in 1901?

Karl Landsteiner, working in Vienna, sorted sera into groups he labelled A, B and C in 1901; the C was later renamed O, and AB was added in 1902.

The Rh blood factor was named after which animal, in whose red cells a similar antigen was found?

Rhesus macaque red cells, injected into rabbits and guinea pigs in 1940, produced the antiserum that defined the factor; the human antigen later proved distinct, but the name stuck.

Which blood type is known as the 'universal donor' for red cell transfusions?

O RhD-negative red cells carry neither A, B nor RhD antigens, so they can be given to almost anyone; hospitals reserve the supply for emergencies and O-negative patients.

Which blood type is called the 'universal recipient'?

AB RhD-positive people carry A, B and RhD antigens on their red cells, so their serum holds no antibodies against any of them and accepts every ABO and Rh type.

Jean-Baptiste Denys, who performed the first animal-to-human transfusion in 1667, was physician to which king?

Louis XIV of France employed Denys as a physician; Denys transfused lamb's blood into a feverish boy in June 1667, and after a later patient died the practice was banned in France.

James Blundell performed the first successful human-to-human blood transfusion in 1818 at which London hospital?

Guy's was Blundell's hospital; he taught midwifery there and at St Thomas', and devised syringes and funnels to move blood straight from donor to patient.

In which city did Bernard Fantus set up the first US hospital blood bank in 1937?

Chicago's Cook County Hospital housed the bank; Fantus, its director of therapeutics, coined the term 'blood bank' for a store of refrigerated donor blood.

Which physician described the circulation of the blood in his 1628 treatise De Motu Cordis?

William Harvey, physician to James I and Charles I, published De Motu Cordis in Frankfurt in 1628, showing that the heart pumps blood around a closed circuit.

Haemophilia is 'the royal disease' because which monarch passed the mutation to royal families across Europe?

Queen Victoria carried the mutation: her son Leopold had haemophilia, and through daughters Alice and Beatrice it reached the royal houses of Russia, Spain and Germany, including Tsarevich Alexei.

Haemophilia A is caused by low levels of which clotting factor?

VIII is the factor deficient in haemophilia A, the commoner form; haemophilia B involves factor IX, and both genes sit on the X chromosome, so males are mostly affected.

Iron-deficiency anaemia, the world's most common cause of anaemia, affects roughly how many people?

About one billion people live with iron-deficiency anaemia, making it the commonest nutritional deficiency on Earth; folate and B12 shortages and thalassaemia are other causes.

Carriers of the sickle cell gene are partly protected against which disease?

Malaria parasites fare worse in red cells carrying one sickle gene, a protective effect Anthony Allison demonstrated in 1954; the trait is commonest where malaria has been endemic.

Leukemia is a cancer of which type of blood cell?

White cells, or leukocytes, multiply abnormally in leukemia; a healthy microlitre of blood carries between four and eleven thousand of them, far fewer than the millions of red cells.

Horseshoe crab blood is bright blue because it carries oxygen with which copper-based protein?

Hemocyanin carries oxygen using copper atoms, turning blue when oxygenated; horseshoe crab blood is also harvested for Limulus amebocyte lysate, a clotting agent that detects bacterial endotoxins.

Skinks of the genus Prasinohaema have green blood because of a build-up of which waste pigment?

Biliverdin, a green bile pigment from haem breakdown, reaches such concentrations in these New Guinea lizards that their blood, muscles, bones and tongues are all green.

Vampire bats, the only mammals that feed solely on blood, are found on which continent?

The Americas, from Mexico to Argentina, are home to all three vampire bat species, each in its own genus; an anticoagulant in their saliva keeps the wound flowing.

The medicinal leech secretes which peptide to stop its host's blood clotting while it feeds?

Hirudin, a 65-amino-acid peptide from the leech's salivary glands, binds thrombin directly; Hirudo medicinalis attaches with a sucker and can take several times its weight in blood.

The red-and-white barber's pole is a relic of which medical practice once performed by barber-surgeons?

Bloodletting was a barber-surgeon's trade: the pole's red recalls blood and the white the bandages, and the practice rested on the ancient idea of balancing the humours.

Which US president asked to be bled heavily after a throat infection, shortly before his death in 1799?

George Washington was bled repeatedly on 14 December 1799, losing an estimated 40 per cent of his blood in a day; he died that evening at Mount Vernon, aged 67.

What does the top, systolic, figure in a blood pressure reading measure?

The peak during a heartbeat is the systolic pressure, reached as the ventricles contract; a resting adult reading under 120/80 mmHg is considered normal.

Which Italian physician introduced the easily usable mercury sphygmomanometer in 1896?

Scipione Riva-Rocci devised the inflatable arm cuff and mercury column in 1896; the American surgeon Harvey Cushing saw it in Italy in 1901 and carried the design home.

The World Health Organization marks World Blood Donor Day on which date?

14 June was chosen because it is the 1868 birthday of the Austrian who discovered the ABO groups; the WHO has marked the day since 2004.

In the United States, how long must a donor wait between whole-blood donations?

56 days, or eight weeks, is the US minimum between whole-blood donations, giving red cells time to rebuild; platelet donors can return after seven days.

The discoverer of the ABO blood groups won the Nobel Prize in Physiology or Medicine in which year?

1930 was the year the Nobel committee honoured the blood-group discovery; the laureate had earlier identified the poliovirus with Erwin Popper and later co-discovered the Rh factor in 1940.

The Belgian doctor Albert Hustin performed the first non-direct (stored) transfusion in which year?

1914 was the year Hustin transfused citrated blood in Brussels; sodium citrate stopped clotting, so blood no longer had to pass directly from donor to patient.

Which protein forms the mesh over a platelet plug to complete a blood clot?

Fibrin strands, cut from soluble fibrinogen by the enzyme thrombin, weave a mesh through the platelet plug; this is the final step of the clotting cascade.

Which vitamin is essential to the clotting cascade and is the target of the anticoagulant warfarin?

The enzyme vitamin K epoxide reductase recycles the vitamin, and warfarin blocks that enzyme.

Blood is a specialised form of which tissue type, according to anatomists?

Connective tissue is the category because blood, like bone and cartilage, consists of cells in an extracellular matrix, here a fluid one, and arises from embryonic mesenchyme.

In 1242 Ibn al-Nafis accurately described which part of the circulation?

Pulmonary circulation, blood passing from the right ventricle through the lungs to the left, was described by Ibn al-Nafis in his commentary on Avicenna's Canon, rejecting Galen's interseptal pores.

Medical words beginning hemo- or haemo- come from which language's word for blood?

Greek supplies the root: haima, 'blood', gives haematology and haemorrhage, while the Latin equivalent sanguis survives in 'sanguine'.

What is the average lifespan of a circulating platelet?

8 to 9 days is the average lifespan of a circulating platelet; old ones are cleared by the spleen, and a microlitre of blood holds roughly 150,000 to 400,000 of them.

Which type of white blood cell belongs to the granulocytes, alongside eosinophils and basophils?

Neutrophils are the most abundant granulocyte, 50 to 70 per cent of circulating leukocytes, and the first responders to bacterial infection; lymphocytes and monocytes are the agranulocytes.

Contrary to the popular myth, what colour is deoxygenated human blood?

Dark red is the colour of venous blood, since the iron pigment absorbs light differently once it gives up oxygen; veins only look blue because skin scatters light.

Which organ receives the most abundant blood supply, at roughly 1,350 ml per minute?

Liver blood flow, from the hepatic artery and portal vein together, is about a quarter of cardiac output, around 1,350 ml a minute, with the kidneys next in line.

By volume, roughly what percentage of blood plasma is water?

92% of the fluid by volume is water; the rest is dissolved proteins such as albumin and globulins, glucose, mineral ions, hormones and waste products.

Which kidney hormone stimulates the bone marrow to make more red cells after blood loss?

Erythropoietin, released mainly by the kidneys when oxygen delivery falls, drives the marrow to produce red cells; synthetic versions were at the centre of cycling's blood-doping scandals.

Robin Fåhræus suggested the Greek theory of four humours came from observing what?

Blood settling into layers in a glass was Fåhræus's idea: drawn blood separates into a dark clot, a red layer, a whitish layer and yellow serum, matching black bile, blood, phlegm and yellow bile.

What is the name of the blood-like body fluid found in invertebrates such as insects?

Hemolymph fills the open body cavity of insects and other arthropods rather than closed vessels; in most insects it carries no oxygen pigment, since air reaches tissues through tracheae.

Which ABO antibodies circulate in the serum of a blood group O person?

Anti-A and anti-B both circulate in group O serum, because O red cells carry neither antigen; those antibodies are why O people can receive only O red cells.