Blood

Bloodis abody fluidin thecirculatory systemofhumansand othervertebratesthat delivers necessary substances such asnutrientsandoxygento thecells, and transportsmetabolic waste productsaway from those same cells.
Blood is composed of blood cells suspended inblood plasma. Plasma, which constitutes 55% of blood fluid, is mostlywater(92% by volume),and containsproteins,glucose, mineralions, andhormones. The blood cells are mainlyred blood cells(erythrocytes),white blood cells(leukocytes), and (in mammals)platelets(thrombocytes).The most abundant cells are red blood cells.These containhemoglobin, which facilitates oxygen transport by reversibly binding to it, increasing its solubility.Jawed vertebrateshave anadaptive immune system, based largely on white blood cells. White blood cells help to resist infections and parasites. Platelets are important in theclottingof blood.
Blood is circulated around the body throughblood vesselsby the pumping action of theheart. In animals withlungs,arterialblood carries oxygen from inhaled air to the tissues of the body, andvenousblood carries carbon dioxide, a waste product ofmetabolismproduced by cells, from the tissues to the lungs to be exhaled. Blood is bright red when its hemoglobin is oxygenated and dark red when it isdeoxygenated.
Medical terms related to blood often begin withhemo-,hemato-,haemo-orhaemato-from the Greek wordαἷμα(haima) for "blood". In terms ofanatomyandhistology, blood is considered a specialized form ofconnective tissue,given its origin in the bones and the presence of potential molecular fibers in the form offibrinogen.
Blood performs many important functions within the body, including:
Blood accounts for 7% of the human body weight,with an average density around 1060 kg/m, very close to pure water's density of 1000 kg/m.The average adult has ablood volumeof roughly 5litres(11 US pt) or 1.3 gallons,which is composed of plasma andformed elements. The formed elements are the two types of blood cell orcorpuscle– thered blood cells, (erythrocytes) andwhite blood cells(leukocytes), and the cell fragments calledplateletsthat are involved in clotting. By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%.
Whole blood (plasma and cells) exhibitsnon-Newtonianfluid dynamics.
One microliter of blood contains:
About 55% of blood isblood plasma, a fluid that is the blood's liquid medium, which by itself is straw-yellow in color. The blood plasma volume totals of 2.7–3.0 liters (2.8–3.2 quarts) in an average human. It is essentially anaqueoussolution containing 92% water, 8% blood plasmaproteins, and trace amounts of other materials. Plasma circulates dissolved nutrients, such asglucose,amino acids, andfatty acids(dissolved in the blood or bound to plasma proteins), and removes waste products, such ascarbon dioxide,urea, andlactic acid.
Other importantcomponentsinclude:
The termserumrefers to plasma from which the clotting proteins have been removed. Most of the proteins remaining are albumin andimmunoglobulins.
Blood pHis regulated to stay within the narrow range of 7.35 to 7.45, making it slightlybasic(compensation).Extra-cellular fluid in blood that has a pH below 7.35 is tooacidic, whereas blood pH above 7.45 is too basic.A pH below 6.9 or above 7.8 is usually lethal.Blood pH,partial pressure of oxygen (pO2),partial pressure of carbon dioxide (pCO2), andbicarbonate(HCO3) are carefully regulated by a number ofhomeostatic mechanisms, which exert their influence principally through therespiratory systemand theurinary systemto control theacid–base balanceand respiration, which is called compensation.Anarterial blood gas testmeasures these. Plasma also circulateshormonestransmitting their messages to various tissues. The list of normalreference rangesfor various blood electrolytes is extensive.
Human blood is typical of that of mammals, although the precise details concerning cell numbers, size,protein structure, and so on, vary somewhat between species. In non-mammalian vertebrates, however, there are some key differences:
Blood is circulated around the body throughblood vesselsby the pumping action of theheart. In humans, blood is pumped from the strongleft ventricleof the heart througharteriesto peripheraltissuesand returns to the rightatrium of the heartthroughveins. It then enters the rightventricleand is pumped through thepulmonary arteryto thelungsand returns to the left atrium through thepulmonary veins. Blood then enters the left ventricle to be circulated again. Arterial blood carries oxygen from inhaled air to all of the cells of the body, andvenous bloodcarries carbon dioxide, a waste product ofmetabolismbycells, to the lungs to be exhaled. However, one exception includes pulmonary arteries, which contain the most deoxygenated blood in the body, while the pulmonary veins contain oxygenated blood.
Additional return flow may be generated by the movement ofskeletal muscles, which can compress veins and push blood through the valves in veins toward theright atrium.
The blood circulation was famously described byWilliam Harveyin 1628.
In vertebrates, the various cells of blood are made in thebone marrowin a process calledhematopoiesis, which includeserythropoiesis, the production of red blood cells; andmyelopoiesis, the production of white blood cells and platelets. During childhood, almost every human bone produces red blood cells; as adults, red blood cell production is limited to the larger bones: the bodies of the vertebrae, the breastbone (sternum), the ribcage, the pelvic bones, and the bones of the upper arms and legs. In addition, during childhood, thethymusgland, found in themediastinum, is an important source ofT lymphocytes.The proteinaceous component of blood (including clotting proteins) is produced predominantly by theliver, while hormones are produced by theendocrine glandsand the watery fraction is regulated by thehypothalamusand maintained by thekidney.
Healthyerythrocyteshave a plasma life of about 120 days before they are degraded by thespleen, and theKupffer cellsin the liver. The liver also clears some proteins, lipids, and amino acids. The kidney actively secretes waste products into theurine.
About 98.5%of theoxygenin a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with thehemoglobin. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen inmammalsand many other species. Hemoglobin has an oxygen binding capacity between 1.36 and 1.40 ml O2per gram hemoglobin,which increases the totalblood oxygen capacityseventyfold,compared to if oxygen solely were carried by its solubility of 0.03 ml O2per liter blood per mm Hg partial pressure of oxygen (about 100 mm Hg in arteries).
With the exception of pulmonary andumbilical arteriesand their corresponding veins, arteries carryoxygenated bloodaway from the heart and deliver it to the body viaarteriolesandcapillaries, where the oxygen is consumed; afterwards,venulesand veins carrydeoxygenated bloodback to the heart.
Under normal conditions in adult humans at rest, hemoglobin in blood leaving the lungs is about 98–99%saturated with oxygen, achieving an oxygen delivery between 950 and 1150 ml/minto the body. In a healthy adult at rest, oxygen consumption is approximately 200–250 ml/min,and deoxygenated blood returning to the lungs is still roughly 75%(70 to 78%)saturated. Increased oxygen consumption during sustained exercise reduces the oxygen saturation of venous blood, which can reach less than 15% in a trained athlete; although breathing rate and blood flow increase to compensate, oxygen saturation in arterial blood can drop to 95% or less under these conditions.Oxygen saturation this low is considered dangerous in an individual at rest (for instance, during surgery under anesthesia). Sustained hypoxia (oxygenation less than 90%), is dangerous to health, and severe hypoxia (saturations less than 30%) may be rapidly fatal.
Afetus, receiving oxygen via theplacenta, is exposed to much lower oxygen pressures (about 21% of the level found in an adult's lungs), so fetuses produce another form of hemoglobin with a much higher affinity for oxygen (hemoglobin F) to function under these conditions.
CO2is carried in blood in three different ways. (The exact percentages vary depending whether it is arterial or venous blood). Most of it (about 70%) is converted to bicarbonate ionsHCO−3by the enzymecarbonic anhydrasein the red blood cells by the reactionCO2+ H2O  →  H2CO3→  H+ HCO−3; about 7% is dissolved in the plasma; and about 23% is bound to hemoglobin ascarbaminocompounds.
Hemoglobin, the main oxygen-carrying molecule in red blood cells, carries both oxygen and carbon dioxide. However, the CO2bound to hemoglobin does not bind to the same site as oxygen. Instead, it combines with the N-terminal groups on the four globin chains. However, because ofallostericeffects on the hemoglobin molecule, the binding of CO2decreases the amount of oxygen that is bound for a given partial pressure of oxygen. The decreased binding to carbon dioxide in the blood due to increased oxygen levels is known as theHaldane effect, and is important in the transport of carbon dioxide from the tissues to the lungs. A rise in the partial pressure of CO2or a lower pH will cause offloading of oxygen from hemoglobin, which is known as theBohr effect.
Some oxyhemoglobin loses oxygen and becomes deoxyhemoglobin. Deoxyhemoglobin binds most of the hydrogen ions as it has a much greater affinity for more hydrogen than does oxyhemoglobin.
In mammals, blood is in equilibrium withlymph, which is continuously formed in tissues from blood by capillary ultrafiltration. Lymph is collected by a system of small lymphatic vessels and directed to thethoracic duct, which drains into the leftsubclavian vein, where lymph rejoins the systemic blood circulation.
Blood circulation transports heat throughout the body, and adjustments to this flow are an important part ofthermoregulation. Increasing blood flow to the surface (e.g., during warm weather or strenuous exercise) causes warmer skin, resulting in faster heat loss. In contrast, when the external temperature is low, blood flow to the extremities and surface of the skin is reduced and to prevent heat loss and is circulated to the important organs of the body, preferentially.
Rate of blood flow varies greatly between different organs. Liver has the most abundant blood supply with an approximate flow of 1350 ml/min. Kidney and brain are the second and the third most supplied organs, with 1100 ml/min and ~700 ml/min, respectively.
Relative rates of blood flow per 100 g of tissue are different, with kidney, adrenal gland and thyroid being the first, second and third most supplied tissues, respectively.
The restriction of blood flow can also be used in specialized tissues to cause engorgement, resulting in anerectionof that tissue; examples are theerectile tissuein thepenisandclitoris.
Another example of a hydraulic function is thejumping spider, in which blood forced into the legs under pressure causes them to straighten for a powerful jump, without the need for bulky muscular legs.
Hemoglobin is the principal determinant of the color of blood (hemochrome). Each molecule has four heme groups, and their interaction with various molecules alters the exact color. Arterial blood and capillary blood are bright red, as oxygen imparts a strong red color to the heme group. Deoxygenated blood is a darker shade of red; this is present in veins, and can be seen duringblood donationand when venous blood samples are taken. This is because the spectrum of light absorbed by hemoglobin differs between the oxygenated and deoxygenated states.
Blood incarbon monoxide poisoningis bright red, becausecarbon monoxidecauses the formation ofcarboxyhemoglobin. Incyanidepoisoning, the body cannot use oxygen, so the venous blood remains oxygenated, increasing the redness. There are some conditions affecting the heme groups present in hemoglobin that can make the skin appear blue – a symptom calledcyanosis. If the heme is oxidized,methemoglobin, which is more brownish and cannot transport oxygen, is formed. In the rare conditionsulfhemoglobinemia, arterial hemoglobin is partially oxygenated, and appears dark red with a bluish hue.
Veins close to the surface of the skin appear blue for a variety of reasons. However, the factors that contribute to this alteration ofcolor perceptionare related to the light-scattering properties of the skin and the processing of visual input by thevisual cortex, rather than the actual color of the venous blood.
Skinksin the genusPrasinohaemahave green blood due to a buildup of the waste productbiliverdin.
Substances other than oxygen can bind to hemoglobin; in some cases, this can cause irreversible damage to the body. Carbon monoxide, for example, is extremely dangerous when carried to the blood via the lungs by inhalation, because carbon monoxide irreversibly binds to hemoglobin to form carboxyhemoglobin, so that less hemoglobin is free to bind oxygen, and fewer oxygen molecules can be transported throughout the blood. This can cause suffocation insidiously. A fire burning in an enclosed room with poor ventilation presents a very dangerous hazard, since it can create a build-up of carbon monoxide in the air. Some carbon monoxide binds to hemoglobin when smoking tobacco.
Blood for transfusion is obtained from human donors byblood donationand stored in ablood bank. There are many differentblood typesin humans, theABO blood group system, and theRhesus blood group systembeing the most important. Transfusion of blood of an incompatible blood group may cause severe, often fatal, complications, socrossmatchingis done to ensure that a compatible blood product is transfused.
Other blood products administeredintravenouslyare platelets, blood plasma, cryoprecipitate, and specific coagulation factor concentrates.
Many forms of medication (fromantibioticstochemotherapy) are administered intravenously, as they are not readily or adequately absorbed by the digestive tract.
After severe acute blood loss, liquid preparations, generically known as plasma expanders, can be given intravenously, either solutions of salts (NaCl, KCl, CaCl2etc.) at physiological concentrations, or colloidal solutions, such as dextrans,human serum albumin, or fresh frozen plasma. In these emergency situations, a plasma expander is a more effective life-saving procedure than a blood transfusion, because the metabolism of transfused red blood cells does not restart immediately after a transfusion.
In modernevidence-based medicine, bloodletting is used in management of a few rare diseases, includinghemochromatosisandpolycythemia. However,bloodlettingandleechingwere common unvalidated interventions used until the 19th century, as many diseases were incorrectly thought to be due to an excess of blood, according toHippocraticmedicine.
Englishblood(Old Englishblod) derives fromGermanicand has cognates with a similar range of meanings in all other Germanic languages (e.g. GermanBlut, Swedishblod, Gothicblōþ). There is no acceptedIndo-Europeanetymology.
Robin Fåhræus(a Swedish physician who devised theerythrocyte sedimentation rate) suggested that the Ancient Greek system ofhumorism, wherein the body was thought to contain four distinct bodily fluids (associated with different temperaments), were based upon the observation of blood clotting in a transparent container. When blood is drawn in a glass container and left undisturbed for about an hour, four different layers can be seen. A dark clot forms at the bottom (the "black bile"). Above the clot is a layer of red blood cells (the "blood"). Above this is a whitish layer of white blood cells (the "phlegm"). The top layer is clear yellow serum (the "yellow bile").
In general, Greek thinkers believed that blood was made from food. Plato and Aristotle are two important sources of evidence for this view, but it dates back to Homer'sIliad.Plato thinks that fire in our bellies transform food into blood.Plato believes that the movements of air in the body as we exhale and inhale carry the fire as it transforms our food into blood.Aristotle believed that food is concocted into blood in the heart and transformed into our body's matter.
The ABO blood group system was discovered in the year 1900 byKarl Landsteiner.Jan Janskýis credited with the first classification of blood into the four types (A, B, AB, and O) in 1907, which remains in use today. In 1907 the firstblood transfusionwas performed that used the ABO system to predict compatibility.The first non-direct transfusion was performed on 27 March 1914. The Rhesus factor was discovered in 1937.
Due to its importance to life, blood is associated with a large number of beliefs. One of the most basic is the use of blood as a symbol for family relationships through birth/parentage; to be "related by blood" is to be related by ancestry or descendence, rather than marriage. This bears closely tobloodlines, and sayings such as "blood is thicker than water" and "bad blood", as well as "Blood brother".
Blood is given particular emphasis in theIslamic,Jewish, andChristianreligions, becauseLeviticus17:11 says "the life of a creature is in the blood." This phrase is part of the Levitical law forbidding the drinking of blood or eating meat with the blood still intact instead of being poured off.
Mythic references to blood can sometimes be connected to the life-giving nature of blood, seen in such events as childbirth, as contrasted with the blood of injury or death.
In manyindigenous Australian Aboriginal peoples'traditions,ochre(particularly red) and blood, both high in iron content and consideredMaban, are applied to the bodies of dancers for ritual. As Lawlor states:
Lawlor comments that blood employed in this fashion is held by these peoples to attune the dancers to the invisible energetic realm of theDreamtime. Lawlor then connects these invisible energetic realms andmagnetic fields, because iron ismagnetic.
Among theGermanic tribes, blood was used during their sacrifices; theBlóts. The blood was considered to have the power of its originator, and, after the butchering, the blood was sprinkled on the walls, on the statues of the gods, and on the participants themselves. This act of sprinkling blood was calledblóedsianinOld English, and the terminology was borrowed by theRoman Catholic Churchbecomingto blessandblessing. TheHittiteword for blood,isharwas a cognate to words for "oath" and "bond", seeIshara.
TheAncient Greeksbelieved that the blood of the gods,ichor, was a substance that was poisonous to mortals.
As a relic of Germanic Law, thecruentation, an ordeal where the corpse of the victim was supposed to start bleeding in the presence of the murderer, was used until the early 17th century.
InGenesis9:4, God prohibitedNoahand his sons from eating blood (seeNoahide Law). This command continued to be observed by theEastern Orthodox Church.
It is also found in the Bible that when the Angel of Death came around to the Hebrew house that the first-born child would not die if the angel saw lamb's blood wiped across the doorway.
At theCouncil of Jerusalem, theapostlesprohibited certain Christians from consuming blood – this is documented in Acts 15:20 and 29. This chapter specifies a reason (especially in verses 19–21): It was to avoid offending Jews who had become Christians, because the Mosaic Law Code prohibited the practice.
Christ's blood is the means for theatonementof sins. Also, "... the blood of Jesus Christ his [God] Son cleanseth us from all sin." (1 John 1:7), "... Unto him [God] that loved us, and washed us from our sins in his own blood." (Revelation 1:5), and "And they overcame him (Satan) by the blood of the Lamb [Jesus the Christ], and by the word of their testimony ..." (Revelation 12:11).
Some Christian churches, including Roman Catholicism,Eastern Orthodoxy,Oriental Orthodoxy, and theAssyrian Church of the Eastteach that, when consecrated, theEucharisticwineactually becomestheblood of Jesusfor worshippers to drink. Thus in the consecrated wine, Jesus becomes spiritually and physically present. This teaching is rooted inthe Last Supper, as written in the four gospels of the Bible, in which Jesus stated to hisdisciplesthat the bread that they ate was his body, and the wine was his blood."This cup is the new testament in my blood, which is shed for you." (Luke 22:20).
Most forms of Protestantism, especially those of aMethodistorPresbyterianlineage, teach that the wine is no more than a symbol of the blood of Christ, who is spiritually but not physically present.Lutherantheology teaches that the body and blood ispresent together "in, with, and under"the bread and wine of the Eucharistic feast.
InJudaism, animal blood may not be consumed even in the smallest quantity (Leviticus 3:17 and elsewhere); this is reflected in Jewishdietarylaws (Kashrut). Blood is purged from meat by rinsing and soaking in water (to loosen clots),saltingand then rinsing with water again several times.Eggs must also be checked and any blood spots removed before consumption.Although blood from fish is biblically kosher, it is rabbinically forbidden to consume fish blood to avoid the appearance of breaking the Biblical prohibition.
Another ritual involving blood involves the covering of the blood offowlandgameafter slaughtering (Leviticus 17:13); the reason given by theTorahis: "Because the life of the animal is [in] its blood" (ibid 17:14). In relation to human beings,Kabbalahexpounds on this verse that theanimal soulof a person is in the blood, and that physical desires stem from it.
Likewise, the mystical reason for salting temple sacrifices and slaughtered meat is to remove the blood of animal-like passions from the person. By removing the animal's blood, the animal energies and life-force contained in the blood are removed, making the meat fit for human consumption.
Consumption of food containing blood is forbidden byIslamic dietary laws. This is derived from the statement in theQur'an, suraAl-Ma'ida(5:3): "Forbidden to you (for food) are: dead meat, blood, the flesh of swine, and that on which has been invoked the name of other than Allah."
Blood is considered unclean, hence there are specific methods to obtain physical and ritual status of cleanliness once bleeding has occurred. Specific rules and prohibitions apply tomenstruation, postnatal bleeding and irregular vaginal bleeding. When an animal has been slaughtered, the animal's neck is cut in a way to ensure that the spine is not severed, hence the brain may send commands to the heart to pump blood to it for oxygen. In this way, blood is removed from the body, and the meat is generally now safe to cook and eat. In modern times, blood transfusions are generally not considered against the rules.
Based on their interpretation of scriptures such as Acts 15:28, 29 ("Keep abstaining...from blood."), manyJehovah's Witnessesneither consume blood nor accept transfusions of whole blood or its major components: red blood cells, white blood cells, platelets (thrombocytes), and plasma. Members may personally decide whether they will accept medical procedures that involve their own blood or substances that are further fractionated from the four major components.
Vampiresare mythical creatures that drink blood directly for sustenance, usually with a preference for human blood. Cultures all over the world have myths of this kind; for example the 'Nosferatu' legend, a human who achievesdamnationand immortality by drinking the blood of others, originates from Eastern European folklore.Ticks,leeches, femalemosquitoes,vampire bats, and an assortment of other natural creatures do consume the blood of other animals, but only bats are associated with vampires. This has no relation to vampire bats, which areNew Worldcreatures discovered well after the origins of the European myths.
In invertebrates, a body fluid analogous to blood called hemolymph is found, the main difference being that hemolymph is not contained in a closed circulatory system. Hemolymph may function to carry oxygen, although hemoglobin is not necessarily used.Crustaceansandmollusksusehemocyanininstead of hemoglobin.In most insects, their hemolymph does not contain oxygen-carrying molecules because their bodies are small enough for theirtracheal systemto suffice for supplying oxygen.
Blood residuecan helpforensicinvestigators identify weapons, reconstruct a criminal action, and link suspects to the crime. Throughbloodstain pattern analysis, forensic information can also be gained from the spatial distribution of bloodstains.
Blood residue analysis is also a technique used inarcheology.
Blood is one of the body fluids that has been used in art.In particular, the performances ofViennese ActionistHermann Nitsch,Istvan Kantor,Franko B,Lennie Lee,Ron Athey,Yang Zhichao,Lucas AbelaandKira O'Reilly, along with the photography ofAndres Serrano, have incorporated blood as a prominent visual element.Marc Quinnhas made sculptures using frozen blood, including a cast of his own head made using his own blood.
The termbloodis used ingenealogical circlesto refer to one'sancestry,origins, andethnic backgroundas in the wordbloodline. Other terms where blood is used in a family history sense areblue-blood,royal blood,mixed-bloodandblood relative.