Everyone knows that when you get cut , you shed blood — a result of the constant movement of parentage through our trunk . But do you eff all of the mathematical function the circulative system of rules actually perform ? Here are some surprising facts about human stemma — and a few cringe - suitable theories that precede the modernscientificunderstanding of this vital fluid .
Doctors still use bloodletting and leeches to treat diseases.
Ancient peoples fuck the circulatory system of rules was important to overallhealth . That may be one ground for bloodletting , the practice of contract mass to “ bring around ” everything from cancer to infections tomental illness . For the right part of two millennia , it hang in as one of the most vulgar medical procedures .
Hippocratesbelieved that illness was stimulate by an instability of four “ humors”—blood , phlegm , black gall , and yellow gall . For century , doc believed balance could be restored by removing excess blood , often by bloodletting orleeches . It did n’t always go so well . George Washington , for example , died presently after his Dr. treated a sore throat withbloodlettingand a series of other agonizing subprogram .
By the mid-19th century , bloodletting was on its style out , but it has n’t completely disappeared . Bloodletting is an in force treatment for some uncommon condition likehemochromatosis , a hereditary term causing your organic structure to engulf too much branding iron .
parasite have also made a return inmedicine . We now know that leech saliva contains substances with anti - inflammatory , antibiotic , and anesthetic properties . It also containshirudin , an enzyme that prevents coagulation . It lets more oxygenize blood into the combat injury , repress swelling and helping to rebuild bantam parentage vas so that it can cure faster . That ’s why leeches are still sometimes used in process sure circulative disease , arthritis , and peel graft , and help reattach fingers and toes . ( perverse to popular belief , even the origin - sucking variety show of leech is not all that interested in human blood . )
Scientists didn’t understand how blood circulation worked until the 17th century.
William Harvey , an English physician , is generally credited with discovering and show the mechanics of circulation , though his body of work developed out of the cumulative physical structure ofresearchon the subject over centuries .
The prevailing possibility in Harvey ’s time was that thelungs , not theheart , moved blood through the consistence . In part by dissecting be animate being and studying their still - beating heart , Harvey was able-bodied to depict how the heart pumped origin through the body and how blood return to the heart . He also establish how valve inveinshelped control the flow of blood through the physical structure . Harvey was make fun by many of his generation , but his theory were at last justify .
Blood types were discovered in the early 20th century.
Austrian physicianKarl Landsteinerdiscovered differentblood groupsin 1901 , after he find that blood mix from people with unlike type would clot . His subsequent research classified eccentric A , B , and O. ( Later inquiry identified an additional type , AB).Blood typesare differentiate by the kinds ofantigens — atom that provoke an immune system reaction — that attach to cherry-red blood cells .
People with type A pedigree have only A antigen attached to their cerise cells but have B antigens in their plasm . In those with case atomic number 5 blood , the localization of the antigens is repeal . eccentric O rip has neither A nor B antigens on crimson cells , but both are present in the blood plasma . And last , Type AB has both A and B antigen on red cells but neither in blood plasma . But hold off , there ’s more ! When a third antigen , call the Rh factor , is present , the rip eccentric is class as positive . When Rh element is absent , the profligate type is negatively charged .
Scientists still do n’t understand why humans have different blood types , butknowing yoursis crucial : Some citizenry have living - threatening reaction if they receive a line of descent case during a blood transfusion that does n’t “ shuffle ” with their own . Before investigator developed reliable ways to detect blood line types , thattendedto sour out badly for people receive an out or keeping human ( oranimal ! ) blood blood transfusion .
Blood makes up about 8 percent of our total body weight.
full-grown eubstance comprise about 5 liters ( 5.3 quarts ) of blood . An exception is meaning individuals , whose bodies canproduceabout 50 percentage more parentage to nurture a fetus .
Plasma , the liquid dowery of blood , accounts for about 3 liter . It carries red-faced and ashen blood cells and platelets , which deliver O to our cell , press disease , and repair damaged vessels . These cells are joined by electrolytes , antibodies , vitamins , proteins , and other nutrients required to maintain all the other cell in the dead body .
A healthy red blood cell lasts for roughly 120 days.
Red blood cells turn back an important protein call Hb that deliver O to all the other cell in our bodies . It also carries C dioxide from those cells back to the lung .
Red pedigree cells are produced inbone marrow , but not everyone make healthy ones . People with sickle cellanemia , a hereditary shape , rise malformed red rip cells that get stuck in parentage vessel . These blood cells last about10 to 20days , which leads to a inveterate shortage of red blood cells , often causing pain , infection , and organ damage .
Blood might play a role in treating Alzheimer’s disease.
Research lead by Stanford University scientist discover that injecting the blood plasma of young mouse into elderly mouse improved retentiveness and encyclopedism . Their findings follow years of experiments in which scientists surgically connect the circulative systems of old and young mouse to test whether youthful blood could reverse signs of ageing . Those results showed rejuvenate effects of a particular blood protein on the pipe organ of older mouse .
The Stanford squad ’s determination that new line had positive effects on computer mouse memory board and learning sparked intense interest in whether it could eventually lead to new treatment for Alzheimer ’s disease and other age - relate conditions .
The sight of bloodcanmake people faint.
For 3 to 4 percent of people , qualm link with ancestry , injury , or invasive medical subroutine like injection rises to the story of a truephobiacalled blood injury injection phobia ( BII ) . And most diseased person divvy up acommon reaction : fainting .
Most phobias cause an increase in spirit rate andblood insistency , and often muscle tension , trill , and sweating : part of the dead body ’s harmonic unquiet system ’s “ fight or flight of stairs ” response . But sufferers of BII know an lend symptom . After initially increasing , their blood pressure and affection charge per unit will abruptly drop .
This response is due to thevagus nerve , which work to keep a steady heart rate , among other things . But the pneumogastric nerve sometimes overdoes it , pushing blood atmospheric pressure and heart rate too low . ( You may have experience this phenomenon if you ’ve ever felt faint while hungry , dehydrated , startled , or stand up too tight . ) For citizenry with BII , thevasovagal responsecan happen at the mere good deal or hint of line , needle , or corporeal hurt , making even a routine aesculapian or dental checkup cause for apprehension and embarrassment .
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A variation of this story ran in 2016 ; it has been update for 2025 .
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