100 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.

In which country is asking someone's blood type a common way to size up personality and romantic compatibility?

Japan treats blood type much like a star sign, and people there are often surprised when a foreigner does not know their own. Scientists dismiss the idea as pseudoscience.

Which toad-shaped North American reptile can squirt an aimed stream of blood from the corners of its eyes?

Horned lizard blood can fly up to 1.5 metres, and canine and feline predators find the taste foul. At least eight species can do it.

Among mosquitoes, all of which sip flower nectar, which ones also bite animals to drink blood?

Females only: in many species a blood meal supplies what the eggs need to develop. Males get by on nectar and plant juices, so they never bite.

Which marine animal has three hearts, two of them serving the gills, pumping bluish blood around its body?

Octopus blood gets its tint from a copper-rich oxygen carrier that works well in cold water. The main heart stops beating whenever the animal swims, so it tires quickly and prefers to crawl.

The idiom 'blue blood', a boast of old noble families who claimed unmixed ancestry, reached English from which language?

Spanish gave English the phrase, first a boast of Castile's oldest families. It probably comes from the blue veins that show through fair skin.

A protein in vampire bat saliva that stops a victim's blood from clotting is named after which fictional vampire?

Dracula gave his name to draculin, which keeps a bite wound flowing while the bat laps at it. Evolution built it from a protein that fights bacteria in other mammals.

Which blood vessels are so narrow that flexible red blood cells must squeeze and deform to pass through them?

Capillaries are only 5 to 10 micrometres across, and their name comes from the Latin for 'resembling hair'. Red cells bend their way through the tightest ones.

Which startup founded by Elizabeth Holmes falsely claimed to run fast, accurate tests on tiny amounts of blood?

Theranos raised more than $700 million and was valued in the billions before its devices were shown not to work as promised. Holmes had started it at the age of 19.

Which sausage from Britain and Ireland is made from pork blood thickened with oatmeal or barley?

Black pudding is a delicacy in Stornoway, whose version has protected status, and in Bury, where it is boiled and served with malt vinegar out of a paper wrapping.

Which mystic won the trust of Russia's last empress by seeming to stop her haemophiliac son's bleeding?

Grigori Rasputin, born a Siberian peasant, was called on whenever young Alexei bled. His sway over the imperial family so alarmed a group of noblemen that they assassinated him in 1916.

Which hormone, released by the pancreas when blood sugar rises, brings the level back down?

Insulin was first isolated in Toronto in 1921, from the pancreas of a dog. Its neighbour hormone glucagon does the opposite job, pushing blood sugar up when it runs low.

Which common painkiller is also taken in low doses to stop blood platelets clumping into clots?

Aspirin switches off each platelet it meets for the rest of that platelet's life, which is why a small dose is enough to help prevent a second heart attack.

Which chemical do forensic investigators spray at crime scenes to make hidden traces of blood glow blue?

Luminol reacts with the iron in blood, but the glow lasts only about 30 seconds, so it has to be photographed in a darkened room. The compound was first made in Germany in 1902.

Which artery, the largest in the human body, runs from the heart down to the abdomen before splitting in two?

The aorta is an elastic artery that stretches each time the heart forces blood into it. It ends low in the abdomen as the left and right common iliac arteries.

Which veins carry blood from the head back to the heart and feature in a phrase about attacking a weak point?

Jugular veins send their blood into the superior vena cava, the great vessel above the heart. To 'go for the jugular' means to attack decisively at the weakest point.

Which religious group refuses blood transfusions on the strength of biblical verses about abstaining from blood?

Jehovah's Witnesses introduced the doctrine in 1945, reading verses in Genesis, Leviticus and Acts as a ban on taking in blood by any route. It is one of the teachings the group is best known for.

In the Book of Exodus, which river is struck with a staff so that its water turns to blood?

The Nile turning to blood is the first of the plagues of Egypt: the fish die, the river stinks, and the Egyptians have to dig along its bank for water they can drink.

Willem Kolff's wartime machine of juice cans and sausage casings cleaned the blood in place of which failing organs?

The kidneys were Kolff's target: his 1943 prototype dialyser also used old car parts. Two years later the machine saved the life of a 67-year-old woman.

Which gas from faulty heaters and car exhausts kills by stopping red blood cells from carrying oxygen?

Carbon monoxide binds tightly to the oxygen carrier in red cells and takes oxygen's place. The 'cherry red skin' that textbooks describe in victims rarely occurs.

Which land mammal needs roughly double a human's blood pressure and has tight leg skin to stop blood pooling?

The giraffe drives that pressure with an 11 kg heart about 60 cm long, all to keep blood flowing up to its brain. Thick skin on the lower legs holds back the blood that gravity pulls down.

The bends, which strikes air-breathing scuba divers who surface too fast, comes from bubbles of which gas in the blood?

Nitrogen dissolves into the body under pressure and comes out of solution as bubbles if that pressure drops too quickly. Victims bend over with joint pain, which is how the bends got its name.

Which fatty substance travels through the blood in LDL particles, the form often nicknamed 'bad'?

Cholesterol barely dissolves in water, so the body ships it around inside lipoprotein parcels. High levels of the LDL kind may raise the risk of cardiovascular disease.

Which organ, built much like a large lymph node, removes old red blood cells and holds a reserve of blood?

The spleen works mainly as a blood filter and recycles the iron from the worn-out cells it removes. Its stored blood can be valuable after a severe haemorrhage.

Which transparent part of the eye has no blood vessels and takes in oxygen dissolved in tears instead?

The cornea has to stay clear, so it does without vessels altogether. That also helps transplants: with no blood supply, a donor cornea causes few problems with rejection.

Which chamber of the heart has the thickest wall because it pumps blood to most of the body?

The left ventricle works at higher pressure than its neighbour on the right, which only fills the lungs. By young adulthood its wall is three to six times thicker.

Because genes A and B both override it, the gene for blood group O is described by geneticists as which type?

Recessive genes stay hidden beside a stronger partner, so only people with two copies of the O gene have type O blood. Two type O parents can therefore only have type O children.

Which herding people of Kenya and Tanzania traditionally drink raw blood taken from their zebu cattle?

The Maasai traditionally lived on raw meat, raw milk, honey and blood, taking the milk daily and the blood only on occasion.

In the old medical theory of four humours, an excess of blood produced which enthusiastic, sociable temperament?

Sanguine people were thought to have too much blood, a humour classed as hot and wet like the season of spring. The word now simply means cheerfully optimistic.

Pernicious anaemia develops when the stomach stops making the protein needed to absorb which nutrient?

Vitamin B12 can only be absorbed once it binds to intrinsic factor, made in the stomach lining. 'Pernicious' means deadly: before treatment existed, the disease was often fatal.

Epistaxis, which most often begins in a patch of vessels called Kiesselbach's plexus, is bleeding from where?

The nose bleeds from the front in most cases; bleeds from further back are rarer but more serious. Only about 6% of people who get one seek medical attention.

Which pets have blood groups called A, B and AB, with type B animals reacting badly to type A blood?

Cats carry ready-made antibodies against the opposite type, so a mismatched transfusion is risky from the start. In one English study, 87% of non-pedigree cats were type A.

Rh-null blood, so rare because it lacks every Rh antigen on its red cells, is nicknamed which kind of blood?

Golden blood is a mixed blessing: red cells with no Rh proteins are misshapen and fragile, which can leave their owner anaemic.

Thalassaemia, a blood disorder first described in Mediterranean families, has a name built from the word for what?

Sea is the meaning of thalassa, the root doctors chose because they first knew the illness as Mediterranean anaemia.

The 'Blue Fugates', a family whose inherited blood condition tinted their skin blue, lived in which US state?

Kentucky's blue family descended from a couple who settled near Hazard about 1820, each carrying the same rare gene. A doctor later eased the colour with a dye, methylene blue.

Which disorder of haem production, once blamed for King George III's 'madness', can make skin blister in sunlight?

Porphyria was proposed as the king's illness in a 1966 paper by two psychiatrists, though others argue he had bipolar disorder. Its skin forms are managed by avoiding sunlight.

Which fish are the only adult vertebrates with colourless blood, relying on oxygen that simply dissolves in it?

Icefish have none of the red pigment that other vertebrates use, so their blood runs clear. A breeding colony found off Antarctica in 2021 held an estimated 60 million nests.

The vampire ground finch, which pecks at seabirds called boobies to drink their blood, is native to which islands?

The Galápagos islands of Wolf and Darwin are its only home. It turns to blood mostly in dry seasons, when seeds and other food are scarce.

Which pigment, left over when the body breaks down old red blood cells, builds up in the skin to cause jaundice?

Bilirubin takes its name from bile and the Latin for red. Light therapy for jaundiced newborns works by reshaping the molecule into a form that dissolves more easily.

James Harrison, whose 1,173 blood donations supplied an antibody that protects unborn babies, came from which country?

Australia retired him at 81, the upper age limit for its donors. His blood carried unusually strong, persistent antibodies used to prevent haemolytic disease of the newborn.

Which Hungarian countess, accused of killing hundreds of girls, was said in later legend to bathe in their blood?

Elizabeth Báthory's blood baths were rumours, written down as fact more than a century after her death. Her servants were executed, while she stayed imprisoned in her castle until she died in 1614.

Which English clergyman made the first published measurement of blood pressure, with tubes in animals' arteries?

Stephen Hales, a Teddington curate, reported the work in his 1733 book Haemastaticks, noting how high the column of blood rose in each tube. He tried it on several animal species.

Which English architect performed the first successful injection of a substance into the bloodstream, using a dog?

Christopher Wren did it at Oxford in the 1650s, years before he designed St Paul's Cathedral. His other early experiments included work on terrestrial magnetism.

In which Italian city do crowds gather three times a year to watch the reputed blood of Saint Januarius liquefy?

Naples has more than 50 official patron saints, but Januarius is the principal one. In 1631 the city called on him to stop an eruption of Mount Vesuvius.

The rare hh blood type, whose carriers can only receive blood from one another, is named after which Indian city?

Bombay is where a doctor first identified the type in 1952. Its carriers can give red cells to any ABO group, yet can safely take them only from each other.

The blood thinner warfarin takes the first half of its name from a research foundation in which US state?

Wisconsin chemists were chasing the toxin in spoiled sweet clover hay that made cattle haemorrhage. Warfarin went on sale in 1948 as a rat poison, six years before it was approved for people.

Which Italian anatomist, magnifying a frog's lungs, first saw the tiny vessels that link arteries to veins?

Marcello Malpighi made the sighting in 1661, after sheep had proved too large to magnify usefully. It supplied the missing link in the theory that blood travels in a closed circuit.

Which ion, the most abundant buffer in the fluid outside cells, mops up excess acid to keep blood pH steady?

Bicarbonate neutralises acids such as lactic acid, and the lungs finish the job by breathing the product out as carbon dioxide. The body keeps about twenty parts of it to one of carbonic acid.

The Duffy blood group system takes its name from Richard Duffy, who played which part in its discovery?

The patient was a haemophiliac whose many transfusions had left his serum with an antibody nobody had seen before. Doctors found it in 1950 and gave the new group his surname.

Which Canadian surgeon ran a mobile blood transfusion service from Madrid during the civil war of the 1930s?

Norman Bethune's unit carried bottled blood from civilian donors to wounded soldiers near the front lines. He died in China in 1939 of septicaemia, and Mao Zedong wrote a eulogy to him.

Which jawless fish clamps onto other fish with a toothed, funnel-like sucking mouth to feed on their blood?

Lamprey ancestors appear to have specialised in the blood and body fluids of other fish, yet only 18 species still hunt this way. The rest never feed on live prey as adults.