50 Fun Facts About Blood

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

The average adult carries about 5 litres of it, at a density only slightly greater than water.

Roughly how much blood does the average adult have?

Roughly 55% of that volume is plasma and 45% is red blood cells.

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

It is 92% water; the term serum refers to plasma with the clotting proteins removed.

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

Each mammalian molecule can bind up to four oxygen molecules, and it is bright red when oxygenated and dark red when not.

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

That is one per haem group; the reversible binding is what makes efficient oxygen transport possible.

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

Their components are salvaged by macrophages, and the marrow replaces them at a rate of hundreds of billions of cells a day.

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

Non-mammalian red cells are flattened, oval and keep their nuclei; the human version is a flexible biconcave disc.

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

The combined surface area of all your red cells would be roughly 2,000 times that of your skin.

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

They have no nucleus and are unique to mammals; other vertebrates clot with small nucleated thrombocytes instead.

Human blood pH is tightly regulated within which narrow range?

A pH below 6.9 or above 7.8 is usually lethal; the lungs and kidneys do most of the balancing.

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

They enter the circulation through permeable sinusoids in the medullary cavity.

Which Austrian physician discovered the ABO blood groups in 1901?

He originally labelled the groups A, B and C; the C later became O.

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

The human factor turned out not to be identical to the monkey's, but by then the name was in worldwide use.

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

Because it is so useful in emergencies, guidelines urge hospitals to reserve it for O-negative patients and true emergencies.

Which blood type is called the 'universal recipient'?

Their red cells carry A, B and RhD antigens, so they carry no antibodies against any of them.

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

He used lamb's and calf's blood; after a patient died, such transfusions were banned for more than a century.

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

He took four ounces of blood from the patient's husband with a syringe to treat her post-partum haemorrhage.

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

He was director of therapeutics at Cook County Hospital, and his lab preserved, refrigerated and stored donor blood.

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

Four centuries earlier, in 1242, the Arab physician Ibn al-Nafis had accurately described the pulmonary circulation.

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

Her son Leopold and, through daughters Alice and Beatrice, the royal houses of Spain, Germany and Russia were affected, including Tsarevich Alexei.

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

Haemophilia B involves factor IX; both genes sit on the X chromosome, which is why the disease overwhelmingly affects males.

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

Anaemia is the most common blood disorder of all; other causes include folate and B12 deficiency and thalassaemia.

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

That protective effect was established in 1954; the disease is most prevalent where malaria has historically been endemic.

Leukemia is a cancer of which type of blood cell?

The name comes from the Greek for 'white'; a healthy microlitre of blood carries 4,000-11,000 of these cells.

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

The blood is harvested for a clotting agent that detects bacterial endotoxins in medicines and implants.

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

Crustaceans and molluscs, meanwhile, have blue blood built around copper rather than iron.

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

There are just three species, each in its own genus, and their saliva contains anticoagulants that keep the wound flowing.

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

Hirudo medicinalis attaches with a sucker; leeches were the tools of choice for centuries of bloodletting.

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

The red stands for blood and the white for the bandages; the practice rested on the ancient theory of balancing the four humours.

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

As late as 1838 a Royal College of Physicians lecturer was still calling the practice a remedy 'hardly possible to estimate too highly'.

Blood pressure is written as one number over another. What does the top (systolic) figure measure?

Normal resting adult pressure is under 120/80 mmHg according to the American Heart Association.

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

The American surgeon Harvey Cushing brought one back to the US and popularised it among doctors.

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

The date is the birthday of the Austrian who discovered the blood groups.

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

Platelet donors can give again after just seven days, and plasma donors twice a week.

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

He had also co-discovered the polio virus in 1909 and, in 1939, the Rh factor.

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

Adding sodium citrate stopped the blood clotting, so it no longer had to flow straight from donor to patient.

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

Several clotting factors depend on a vitamin that the anticoagulant warfarin blocks the body from recycling.

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?

The classification comes from its structure: cells and cell fragments suspended in a fluid matrix.

In 1242 Ibn al-Nafis accurately described which part of the circulation, centuries before Harvey?

He still believed, as the ancients did, that a 'vital spirit' was formed in the left ventricle.

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

The root is haima; the study of blood is haematology.

What is the average lifespan of a circulating platelet?

A microlitre of blood carries 200,000-500,000 of them, ready to plug any break in a vessel wall.

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

Lymphocytes (T and B cells) and monocytes are the agranulocytes.

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

The 'blue veins' you see are an effect of skin and light; blood only looks blue in animals with copper-based pigment.

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

The kidneys and brain come second and third, though per 100 g of tissue the kidney, adrenal gland and thyroid are the most richly supplied.

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

The rest is proteins, glucose, mineral ions and hormones; plasma itself makes up about 55% of blood.

What is the first symptom of blood loss, appearing after a healthy adult loses about 20% of volume?

That is about a litre; shock sets in at roughly 40% of blood volume, or two litres.

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

Left undisturbed for an hour, drawn blood forms a dark clot, a red-cell layer, a whitish white-cell layer and clear yellow serum on top.

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

Unlike blood it is not held in a closed circulatory system, and in most insects it carries no oxygen-transporting molecules at all.

According to Plato, what transformed food into blood inside the body?

Aristotle instead placed the transformation in the heart; the idea that blood is made from food goes back to Homer's Iliad.