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BloodBlood carries nourishment and oxygen throughout the body and carries away waste products. The earliest evidence in the fossil record of a blood-like substance, found on the remains of an armored arthropod, dates to at least 520 million years ago. Blood has evolved several times across the animal kingdom, giving rise to substances of different colors, compositions, and purposes. Yet not all animals require it: Some have developed alternative workarounds, including obtaining the oxygen they need from their environment. Humans' blood appears red due to its iron base, though blood veins appear blue because of how light and skin scatter colors. There are numerous blood types in humans, determined by the presence or absence of specific A and/or B antigens and also the presence or absence of a certain protein, called Rh factor. Different permutations of those combinations result in the eight main known blood types, though there are more than 40 human blood types overall. The eight main blood types are A, B, AB, and O, with positive and negative variations. A person's blood type determines how their immune system responds to foreign blood following a transfusion.Explore Blood
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Blood color differs across the animal kingdom, with some animals producing blood that appears green (a group of lizards in New Guinea) or blue (horseshoe crabs). American Museum of Natural HistoryExplore this blood type interactive to learn more about how the 8 most common blood types are defined.
American Red CrossWithout the option of modern blood transfusions, some doctors in the mid-1800s tried to help save cholera patients by injecting them with cow's milk, hoping it would boost their nutrition and hydration. Tiny MattersWhile nearly all fish are cold-blooded—their body temperatures match their surroundings—the opah, or moonfish, is fully warm-blooded, with a body temperature about 5 degrees Celsius (9 degrees Fahrenheit) warmer than its environment. IFLScienceBlood moons only occur during total lunar eclipses, when the Earth blocks the sun, but its atmosphere lets redder parts of sunlight through to reflect off the lunar surface. Time and DateSee how the Ebola virus affects blood circulation in the human body. STATCertain medications that affect blood flow or mood boost the risk of heatstrokeDrugs that narrow blood vessels, beta blockers that regulate blood pressure, diuretics, antidepressants, and antipsychotics can all affect the body's ability to regulate its internal body temperature, and so individuals taking these medications need to take special care in extreme heat and when exercising in hot conditions. NBC NewsThere are two FDA-approved blood tests that may detect early Alzheimer's diseaseYet the tests are only recommended for those who have symptoms of dementia, and are not definitive on their own. False positives are a concern with these new tests, which detect biomarkers that may indicate the presence of brain proteins linked to the disease. This podcast explores the state of research on the disease and concerns about regulators taking jobs at pharmaceutical and biotech companies, which may influence their approach to approvals. It also dives into an investigation about the data underpinning one experimental Alzheimer's drug. FreakonomicsPregnancy causes a woman's blood volume to increase by up to 50%This change, to support the developing fetus, puts stress on the heart and blood vessels. A pregnant woman's heart rate also increases as she pumps more blood each minute to support fetal growth. Mayo ClinicGenetic blood test offers an estimated clock on when Alzheimer's symptoms may appearThe 2026 research finding from researchers at Washington University School of Medicine in St. Louis—if validated in broader populations—suggests that an already available blood test could estimate when Alzheimer's symptoms may begin within a margin of several years. The test detects a protein called p-tau217 found in blood plasma and the researchers incorporated the findings from that blood test into a statistical model to come up with the symptom timeline predictions. Medical News TodayUntreated malaria can lead to blocked blood vessels in the brain, coma, and organ failure. Cleveland ClinicBlood tests for Lyme disease tend to come up as false negatives in the week after a biteIt can take several weeks for Lyme antibodies to develop, which is what blood tests would be detecting. That's why many clinicians will prescribe antibiotic treatment immediately after a bite if the individual develops the characteristic bullseye rash of Lyme or gets bitten in an area of the country known to have high rates of Lyme. Columbia University Irving Medical CenterWhile most cells possess DNA, red blood cells destroy their nuclei to maximize the amount of oxygen they carry and more easily alter their shape to fit through narrow blood capillaries. West Texas A&M UniversityEnglishmen in the 17th century mixed their blood into wine to show devotionIn order to demonstrate their love for a woman, some young Englishmen would stab themselves in the arm and mix the blood into their wine. They'd then toast the object of their affection and drink to their honor. NPRCold-blooded reptiles seek heat, and that behavior may help combat fungal infectionsThis Radiolab podcast episode takes on the idea that though our human bodies are too warm for the majority of fungal species to effectively replicate inside our bodies, that's not the case for reptiles. Yet when those species warm their bodies by basking in the sun on rocks, they can soak up heat and may also help keep fungal infections in check. RadiolabHow much your blood really costsIn the US, donating plasma twice a week can earn you $400 a month. But this system only works by targeting people who need the money most. Plasma clinics are placed in low-income zip codes, and frequent donation may increase health risks. 1440Inside 'Blood Meridian' author Cormac McCarthy's library of 20,000 booksThe reclusive writer published 12 novels and taught himself stonemasonry and quantum physics, among myriad other skills and subjects. Since he died in 2023, scholars have been mining his personal library for lessons on his influences, interests, and more. Smithsonian MagazineNanoplastics can bypass the blood-brain barrier and may harm the nervous systemNanoplastics are formed from the breakdown of microplastics and can breach cells. Their large surface area relative to size allows them to carry higher concentrations of forever chemicals than the surrounding environment into sensitive organs. It's Complicated'Golden blood' is the rarest blood type in the world—fewer than 50 people are known to have it.Rh-null, also known as “golden blood,” is a blood type so rare, fewer than 50 people are known to have it. It lacks all 61 Rh antigens, making it a universal donor for rare Rh cases, but a nightmare in emergencies, since only Rh-null can be given back. 1440 Trials ongoing for a 99% accurate, AI-powered blood testThe UK's National Health Service has launched a trial for a blood test that can detect a dozen types of cancers with just ten drops of blood. An AI tool looks for genetic material known to be released by tumors, allowing for cancer detection before tumors are large enough to be imaged. Sky NewsFentanyl is better at crossing the blood-brain barrier than other opioidsAmong opioids, fentanyl is uniquely adept at crossing the blood-brain barrier—the brain's security fence against harmful substances. This enables a lightning-fast high. It ends just as quickly, sometimes within minutes (where a heroin high lasts hours), and still results in the same withdrawal symptoms. KurzgesagtBears may have evolved natural mechanisms to prevent blood clots during hibernation, an important development, since inactivity typically leads to blood clots in other animals.You’ve almost certainly been told the importance of moving around on long flights to prevent blood clots. But have you ever wondered why hibernating bears don’t suffer the same problems while lying still for months? In this fascinating article, we learn that researchers have recently discovered that lower concentrations of a specific protein may explain the phenomenon. Learn all about the latest findings and how they may influence the future of blood clot medicine in humans. ScienceHow tPA, which helps dissolve blood clots, can lessen the severity of a strokeOne of the most exciting recent advances in treating stroke is a medication known as tissue plasminogen activator, or tPA. It is only effective for use in some ischemic strokes, and it must be delivered within 4.5 hours of symptom onset to have a chance at working. Barrow Neurological InstituteBlood clotting is critical to maintaining life, but dysfunctional clots can be fatal.The process of blood clotting is a natural phenomenon that is critical to maintaining life — it’s how our body stops bleeding in the event of an injury. However, if the system clots inappropriately within the blood vessels, the outcomes can be fatal. This helpful resource from the NIH outlines the basics of clotting, what causes this elegant system to malfunction within our bodies, and what the subsequent consequences may be depending on where the mistaken clot occurred. MedlinePlusA stroke occurs when blood flow to part of the brain is suddenly interrupted, either by a blockage (ischemic stroke) or bleeding when a blood vessel in the brain breaks and bleeds (hemorrhagic stroke). One out of every six people will have a stroke at some point during their lives. But what causes a stroke in the first place? This short, animated video from Ted-ED takes a look at the different reasons why strokes occur, what happens to the brain as a result, and what medical providers can do to treat them. TED-EdExercise improves brain blood flow, stimulates neural growth, and moreExercise has dramatic effects on human biology, including reducing some of the long-term harms associated with chronic stress. Its effects are also pronounced in the brain, including improved memory retention, sleep, cognitive functioning, and more. TED TalksWhat is the blood brain barrier?Every blood vessel is lined with endothelial cells that act as filters between blood and the rest of the body. In the brain, these cells are tightly packed together to keep a close watch on what substances can access the vital organ. This protective measure poses an obstacle to drugmakers looking to deliver drugs to the well-defended brain for conditions like Alzheimer's. Watch a quick overview here. STATTruman Capote's 'In Cold Blood,' a pioneer of the true crime genre, isn't wholly accurateThe nonfiction novel "In Cold Blood" influenced true crime's narrative and investigative bend and was supposedly only 92% accurate. Journalist Ben Yagoda reflects on its accuracy after finding the fact-checking file for the four-part series published before the story was converted into hardback. Yagoda says the inaccuracies are "especially striking" because the story was originally published in one of the magazines credited with establishing fact-checking as a practice. (Some users may experience a paywall.) SlateThe strange endurance of consuming blood for healthBlood's importance to humanity is best summarized this way: without it, we die. This importance naturally begets assumptions about its medicinal properties, many of which appear accessible through drinking or eating the fluid connective tissue. This article details the history of blood drinking, from ancient Roman gladiators to modern-day sanguinarians. Atlas ObscuraHow did segregation in the US affect blood donations?When the US established its first nationwide network of blood banks in 1941 with the hopes of restoring the dwindling reserves of military members, it was quick to emphasize blood donated by Black Americans wouldn't coat the veins of white servicemen. Historians say this policy was meant to appease white Southerners who believed Black blood was inferior to their own.This policy was leaked to the press that same year. Undark MagazineThe economics of horseshoe crab blood Horseshoe crabs are older than dinosaurs and have survived five mass extinctions that wiped most life from the planet. But it's only now that their future as a species is in danger. This blood, worth about $60,000 per gallon, is hyper-sensitized to certain bacteria that are fatal to humans. This 17-minute podcast dives into humanity's pursuit of horseshoe crab blood, a "somewhat magical" mixture heavily relied on by the pharmaceutical industry. The Economics of Everyday ThingsWhy don't we synthesize blood?We're trying. Scientists are currently working on creating viable synthetic blood, an alternative to the presently relied-upon donations that manage to fall short of demand. More than half of the world's nations struggle to meet their population's need for blood. This article details current and historical efforts to develop synthetic blood, a venture that started more than 400 years ago. VoxWhen was the first blood transfusion?In the 1600s, an English doctor transferred the blood from one dog to another via quills. The procedure ended when one of the dogs died. This article details the early days of blood transfusions, which turned toward humans shortly after the 1666 dog experiment and involved putting the blood of a sheep into a human recipient (who reportedly survived the encounter). JSTORThe ultrarare 'Er' blood type has been documented only about 40 times, and it can cause devastating pregnancy complications.The tragic loss of a pregnancy in 2022 led researchers to the discovery that the rare 'Er' blood type could potentially cause a mismatch in blood types between mother and fetus during pregnancy, with devastating consequences. WIREDA brief history of human blood groupsThe blood group that determines whether you have type A, B, AB, or O blood was discovered near the turn of the 20th century. This short academic article dives into three main theories about the evolution and emergence of blood groups, the exact nature of which remains unclear. National Institutes of HealthThe history of blood, as told by a hematologist Since ancient times, blood has been seen as a semi-magical substance. Alchemists theorized it was a mixture of the four elements. Others proposed it was one of four bodily fluids whose balance dictated health. This 2019 essay by a hematologist reviews blood's reputation across cultures and centuries. The New YorkerAn interactive explanation of blood transfusionThe antigens and Rh factors of blood cells (which determines your blood type) must be compatible with your immune system—which is why blood transfusions between patients must have matching types. In a mismatch, the immune system will attack and destroy donor blood cells, triggering a potentially fatal reaction. Nobel PrizeSeven things you might not know about bloodThe red stuff currently pumping throughout your body is a type of connective tissue that is both a solid and a liquid. The liquid portion—plasma—acts as a carrier for the solid portion, which includes blood cells and their biological brethren. Your body is constantly refreshing its supply of blood, creating new cells to replace those that have expired or died. This article overviews some lesser-known facts about blood (and why it's not always red). The ConversationBone marrow generates roughly 500 billion new blood cells each day.Some of our bones are stuffed to the brim with a fatty, jam-like substance called marrow. Bone marrow comes in yellow and red, with the latter responsible for producing new blood cells, and has become critical in treating diseases like leukemia. Institute of Human AnatomyNew blood cells are created by hematopoietic stem cellsBlood is made up of several cells with various functions and short lifespans, so the body must have a constant supply of replacements. These replacements are created by hematopoietic stem cells, rare cells that live in bone marrow and can regenerate themselves and blood cells. Stem Cell NetworkWhat does blood do?Blood's primary purpose is to ferry oxygen and nutrients to cells in need while collecting cell waste and byproducts for removal. It also enables the body's repair and immune systems to traverse our internal landscape to address cell damage or external invaders, such as viruses and parasites. Zooming out from the exact roles of blood's various cells, the fluid connective tissue also assists with maintaining homeostasis via temperature regulation and pH balance. OpenStax/Oregon State UniversityBlood has evolved many times over hundreds of millions of years, resulting in different blood colors and compositions—and there are even some organisms that don't need blood at all.The earliest evidence of a blood-like substance comes from ancient arthropods, which appear to have copper-based blood. In the 500 million years since then, some creatures have grown to rely on other variants, such as humanity's iron-based blood. PBS EonsInsulin is a hormone that controls blood sugar by helping absorb it into cellsBlood sugar levels increase after a meal when the body starts turning food into usable fuel—sugars, proteins, and more—which are absorbed into the bloodstream through the intestines. Blood sugar levels rise, releasing insulin, and letting sugar in the blood be absorbed into hungry cells, thereby dropping blood sugar levels. NatureThe pancreas releases digestive enzymes and regulates blood sugarThe pancreas weighs about the same as a deck of cards and is smaller than the average adult human hand. This lopsided glandular organ controls blood sugar levels through insulin production and helps the body digest food by creating a neutralizing tonic filled with digestive enzymes. TED-EdThe Hungarian countess rumored to have bathed in bloodAccording to legend, Hungarian countess Elizabeth Báthory killed up to 600 women to bathe in their blood and preserve her youth. Such allegations have been challenged since the 1980s when Slovakian archivist Josef Kocis published a book detailing new aspects of Báthory's life and included possible evidence of a conspiracy meant to undermine her power as part of Transylvania's ruling dynasty. National GeographicThe bloody history of the true crime genreThe true crime genre appears to have crawled out of an unlocked closet between 1550 and 1700. Rising literacy rates and printing technologies during this period led to leaflets and ballads-turned-broadsides that graphically regurgitated the findings. These products often included woodcuts of the crime's "unsavory acts.". Such content was snapped up by the "artisan class and above" as poorer classes lacked the funds to fuel the hobby. JSTORWhy hibernating bears don't get blood clotsFor mammals, long periods of inactivity can lead to health problems—blood flow slows and pools, veins kink and distort, and clots potentially form. Hibernation takes this risk to the extreme, yet for decades why animals like bears did not exhibit... The ScientistBlood pressure readings correspond to the peaks and valleys of heart beatsPushing 2,000 gallons of blood through the body every day exerts a force known as blood pressure. Blood pressure is highest during the heart's contractile phase, known as systole, which forces blood through the circulatory system, and lowest during the heart's resting phase between beats, known as diastole. TED TalksExplore the microscopic composition of blood.Visually, blood looks like a single, red fluid. Zooming in, it is one of the richest substances known, with hemoglobin, plasma, proteins, red and white blood cells, platelets, and more. Visual CapitalistBlood Pressure and DiabetesNew meta-analysis shows blood pressure reductions with ACE inhibitors and ARBs are associated with a lower diabetes risk, but other types of antihypertensive agents have the opposite effect. Medscape
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