Blood | Wikipedia audio article

Blood is a body fluid in humans and other
animals that delivers necessary substances such as nutrients and oxygen to the cells
and transports metabolic waste products away from those same cells.In vertebrates, it is
composed of blood cells suspended in blood plasma. Plasma, which constitutes 55% of blood fluid,
is mostly water (92% by volume), and contains proteins, glucose, mineral ions, hormones,
carbon dioxide (plasma being the main medium for excretory product transportation), and
blood cells themselves. Albumin is the main protein in plasma, and
it functions to regulate the colloidal osmotic pressure of blood. The blood cells are mainly red blood cells
(also called RBCs or erythrocytes), white blood cells (also called WBCs or leukocytes)
and platelets (also called thrombocytes). The most abundant cells in vertebrate blood
are red blood cells. These contain hemoglobin, an iron-containing
protein, which facilitates oxygen transport by reversibly binding to this respiratory
gas and greatly increasing its solubility in blood. In contrast, carbon dioxide is mostly transported
extracellularly as bicarbonate ion transported in plasma. Vertebrate blood is bright red when its hemoglobin
is oxygenated and dark red when it is deoxygenated. Some animals, such as crustaceans and mollusks,
use hemocyanin to carry oxygen, instead of hemoglobin. Insects and some mollusks use a fluid called
hemolymph instead of blood, the difference being that hemolymph is not contained in a
closed circulatory system. In most insects, this “blood” does not contain
oxygen-carrying molecules such as hemoglobin because their bodies are small enough for
their tracheal system to suffice for supplying oxygen. Jawed vertebrates have an adaptive immune
system, based largely on white blood cells. White blood cells help to resist infections
and parasites. Platelets are important in the clotting of
blood. Arthropods, using hemolymph, have hemocytes
as part of their immune system. Blood is circulated around the body through
blood vessels by the pumping action of the heart. In animals with lungs, arterial blood carries
oxygen from inhaled air to the tissues of the body, and venous blood carries carbon
dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to
be exhaled. Medical terms related to blood often begin
with hemo- or hemato- (also spelled haemo- and haemato-) from the Greek word αἷμα
(haima) for “blood”. In terms of anatomy and histology, blood is
considered a specialized form of connective tissue, given its origin in the bones and
the presence of potential molecular fibers in the form of fibrinogen.==Functions==Blood performs many important functions within
the body, including: Supply of oxygen to tissues (bound to hemoglobin,
which is carried in red cells) Supply of nutrients such as glucose, amino
acids, and fatty acids (dissolved in the blood or bound to plasma proteins (e.g., blood lipids))
Removal of waste such as carbon dioxide, urea, and lactic acid
Immunological functions, including circulation of white blood cells, and detection of foreign
material by antibodies Coagulation, the response to a broken blood
vessel, the conversion of blood from a liquid to a semisolid gel to stop bleeding
Messenger functions, including the transport of hormones and the signaling of tissue damage
Regulation of core body temperature Hydraulic functions==
In mammals===Blood accounts for 7% of the human body weight,
with an average density around 1060 kg/m3, very close to pure water’s density of 1000
kg/m3. The average adult has a blood volume of roughly
5 litres (11 US pt), which is composed of plasma and several kinds of cells. These blood cells (which are also called corpuscles
or “formed elements”) consist of erythrocytes (red blood cells, RBCs), leukocytes (white
blood cells), and thrombocytes (platelets). 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) exhibits non-Newtonian
fluid dynamics. If all human hemoglobin were free in the plasma
rather than being contained in RBCs, the circulatory fluid would be too viscous for the cardiovascular
system to function effectively.====Cells====One microliter of blood contains: 4.7 to 6.1 million (male), 4.2 to 5.4 million
(female) erythrocytes: Red blood cells contain the blood’s hemoglobin and distribute oxygen. Mature red blood cells lack a nucleus and
organelles in mammals. The red blood cells (together with endothelial
vessel cells and other cells) are also marked by glycoproteins that define the different
blood types. The proportion of blood occupied by red blood
cells is referred to as the hematocrit, and is normally about 45%. The combined surface area of all red blood
cells of the human body would be roughly 2,000 times as great as the body’s exterior surface. 4,000–11,000 leukocytes: White blood cells
are part of the body’s immune system; they destroy and remove old or aberrant cells and
cellular debris, as well as attack infectious agents (pathogens) and foreign substances. The cancer of leukocytes is called leukemia. 200,000–500,000 thrombocytes: Also called
platelets, they take part in blood clotting (coagulation). Fibrin from the coagulation cascade creates
a mesh over the platelet plug.====Plasma====About 55% of blood is blood 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 an aqueous solution containing
92% water, 8% blood plasma proteins, and trace amounts of other materials. Plasma circulates dissolved nutrients, such
as glucose, amino acids, and fatty acids (dissolved in the blood or bound to plasma proteins),
and removes waste products, such as carbon dioxide, urea, and lactic acid. Other important components include: Serum albumin
Blood-clotting factors (to facilitate coagulation) Immunoglobulins (antibodies)
lipoprotein particles Various other proteins
Various electrolytes (mainly sodium and chloride)The term serum refers to plasma from which the
clotting proteins have been removed. Most of the proteins remaining are albumin
and immunoglobulins.====pH values====Blood pH is regulated to stay within the narrow
range of 7.35 to 7.45, making it slightly basic. Blood that has a pH below 7.35 is too acidic,
whereas blood pH above 7.45 is too basic. Blood pH, partial pressure of oxygen (pO2),
partial pressure of carbon dioxide (pCO2), and bicarbonate (HCO3−) are carefully regulated
by a number of homeostatic mechanisms, which exert their influence principally through
the respiratory system and the urinary system to control the acid-base balance and respiration. An arterial blood gas test measures these. Plasma also circulates hormones transmitting
their messages to various tissues. The list of normal reference ranges for various
blood electrolytes is extensive.===In non-mammalian vertebrates===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: Red blood cells of non-mammalian vertebrates
are flattened and ovoid in form, and retain their cell nuclei. There is considerable variation in the types
and proportions of white blood cells; for example, acidophils are generally more common
than in humans. Platelets are unique to mammals; in other
vertebrates, small nucleated, spindle cells called thrombocytes are responsible for blood
clotting instead.==Physiology=====Cardiovascular system===Blood is circulated around the body through
blood vessels by the pumping action of the heart. In humans, blood is pumped from the strong
left ventricle of the heart through arteries to peripheral tissues and returns to the right
atrium of the heart through veins. It then enters the right ventricle and is
pumped through the pulmonary artery to the lungs and returns to the left atrium through
the pulmonary 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, and venous blood carries carbon dioxide, a waste product
of metabolism by cells, 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 of skeletal muscles, which can compress veins and push blood through the
valves in veins toward the right atrium. The blood circulation was famously described
by William Harvey in 1628.===Production and degradation of blood cells
===In vertebrates, the various cells of blood
are made in the bone marrow in a process called hematopoiesis, which includes erythropoiesis,
the production of red blood cells; and myelopoiesis, 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, the thymus
gland, found in the mediastinum, is an important source of T lymphocytes. The proteinaceous component of blood (including
clotting proteins) is produced predominantly by the liver, while hormones are produced
by the endocrine glands and the watery fraction is regulated by the hypothalamus and maintained
by the kidney. Healthy erythrocytes have a plasma life of
about 120 days before they are degraded by the spleen, and the Kupffer cells in the liver. The liver also clears some proteins, lipids,
and amino acids. The kidney actively secretes waste products
into the urine.===Oxygen transport===About 98.5% of the oxygen in a sample of arterial
blood in a healthy human breathing air at sea-level pressure is chemically combined
with the hemoglobin. 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 in mammals and many other species (for exceptions, see below). Hemoglobin has an oxygen binding capacity
between 1.36 and 1.40 ml O2 per gram hemoglobin, which increases the total blood oxygen capacity
seventyfold, compared to if oxygen solely were carried by its solubility of 0.03 ml
O2 per liter blood per mm Hg partial pressure of oxygen (about 100 mm Hg in arteries).With
the exception of pulmonary and umbilical arteries and their corresponding veins, arteries carry
oxygenated blood away from the heart and deliver it to the body via arterioles and capillaries,
where the oxygen is consumed; afterwards, venules and veins carry deoxygenated blood
back 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/min to 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.A fetus, receiving oxygen via the placenta, 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.===Carbon dioxide transport===
CO2 is 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
ions HCO−3 by the enzyme carbonic anhydrase in the red blood cells by the reaction CO2
+ H2O → H2CO3 → H+ + HCO−3; about 7% is dissolved in the plasma; and about 23%
is bound to hemoglobin as carbamino compounds.Hemoglobin, the main oxygen-carrying molecule in red blood
cells, carries both oxygen and carbon dioxide. However, the CO2 bound 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 of allosteric effects on
the hemoglobin molecule, the binding of CO2 decreases 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 the Haldane effect, and is important
in the transport of carbon dioxide from the tissues to the lungs. A rise in the partial pressure of CO2 or a
lower pH will cause offloading of oxygen from hemoglobin, which is known as the Bohr effect.===Transport of hydrogen ions===
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.===Lymphatic system===In mammals, blood is in equilibrium with lymph,
which is continuously formed in tissues from blood by capillary ultrafiltration. Lymph is collected by a system of small lymphatic
vessels and directed to the thoracic duct, which drains into the left subclavian vein
where lymph rejoins the systemic blood circulation.===Thermoregulation===
Blood circulation transports heat throughout the body, and adjustments to this flow are
an important part of thermoregulation. 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===
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.===Hydraulic functions===
The restriction of blood flow can also be used in specialized tissues to cause engorgement,
resulting in an erection of that tissue; examples are the erectile tissue in the penis and clitoris. Another example of a hydraulic function is
the jumping 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.===Invertebrates===
In insects, the blood (more properly called hemolymph) is not involved in the transport
of oxygen. (Openings called tracheae allow oxygen from
the air to diffuse directly to the tissues.) Insect blood moves nutrients to the tissues
and removes waste products in an open system. Other invertebrates use respiratory proteins
to increase the oxygen-carrying capacity. Hemoglobin is the most common respiratory
protein found in nature. Hemocyanin (blue) contains copper and is found
in crustaceans and mollusks. It is thought that tunicates (sea squirts)
might use vanabins (proteins containing vanadium) for respiratory pigment (bright-green, blue,
or orange). In many invertebrates, these oxygen-carrying
proteins are freely soluble in the blood; in vertebrates they are contained in specialized
red blood cells, allowing for a higher concentration of respiratory pigments without increasing
viscosity or damaging blood filtering organs like the kidneys. Giant tube worms have unusual hemoglobins
that allow them to live in extraordinary environments. These hemoglobins also carry sulfides normally
fatal in other animals.==Color==
The coloring matter of blood (hemochrome) is largely due to the protein in the blood
responsible for oxygen transport. Different groups of organisms use different
proteins.===Hemoglobin===Hemoglobin is the principal determinant of
the color of blood in vertebrates. Each molecule has four heme groups, and their
interaction with various molecules alters the exact color. In vertebrates and other hemoglobin-using
creatures, 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 during blood donation and when venous blood
samples are taken. This is because the spectrum of light absorbed
by hemoglobin differs between the oxygenated and deoxygenated states.Blood in carbon monoxide
poisoning is bright red, because carbon monoxide causes the formation of carboxyhemoglobin. In cyanide poisoning, the body cannot utilize
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 called
cyanosis. If the heme is oxidized, methemoglobin, which
is more brownish and cannot transport oxygen, is formed. In the rare condition sulfhemoglobinemia,
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 of color perception are related to the light-scattering properties of the
skin and the processing of visual input by the visual cortex, rather than the actual
color of the venous blood.Skinks in the genus Prasinohaema have green blood due to a buildup
of the waste product biliverdin.===Hemocyanin===The blood of most mollusks – including cephalopods
and gastropods – as well as some arthropods, such as horseshoe crabs, is blue, as it contains
the copper-containing protein hemocyanin at concentrations of about 50 grams per liter. Hemocyanin is colorless when deoxygenated
and dark blue when oxygenated. The blood in the circulation of these creatures,
which generally live in cold environments with low oxygen tensions, is grey-white to
pale yellow, and it turns dark blue when exposed to the oxygen in the air, as seen when they
bleed. This is due to change in color of hemocyanin
when it is oxidized. Hemocyanin carries oxygen in extracellular
fluid, which is in contrast to the intracellular oxygen transport in mammals by hemoglobin
in RBCs.===Chlorocruorin===The blood of most annelid worms and some marine
polychaetes use chlorocruorin to transport oxygen. It is green in color in dilute solutions.===Hemerythrin===Hemerythrin is used for oxygen transport in
the marine invertebrates sipunculids, priapulids, brachiopods, and the annelid worm, magelona. Hemerythrin is violet-pink when oxygenated.===Hemovanadin===The blood of some species of ascidians and
tunicates, also known as sea squirts, contains proteins called vanadins. These proteins are based on vanadium, and
give the creatures a concentration of vanadium in their bodies 100 times higher than the
surrounding sea water. Unlike hemocyanin and hemoglobin, hemovanadin
is not an oxygen carrier. When exposed to oxygen, however, vanadins
turn a mustard yellow.==Pathology=====General medical disorders===
Disorders of volume Injury can cause blood loss through bleeding. A healthy adult can lose almost 20% of blood
volume (1 L) before the first symptom, restlessness, begins, and 40% of volume (2 L) before shock
sets in. Thrombocytes are important for blood coagulation
and the formation of blood clots, which can stop bleeding. Trauma to the internal organs or bones can
cause internal bleeding, which can sometimes be severe. Dehydration can reduce the blood volume by
reducing the water content of the blood. This would rarely result in shock (apart from
the very severe cases) but may result in orthostatic hypotension and fainting. Disorders of circulation
Shock is the ineffective perfusion of tissues, and can be caused by a variety of conditions
including blood loss, infection, poor cardiac output. Atherosclerosis reduces the flow of blood
through arteries, because atheroma lines arteries and narrows them. Atheroma tends to increase with age, and its
progression can be compounded by many causes including smoking, high blood pressure, excess
circulating lipids (hyperlipidemia), and diabetes mellitus. Coagulation can form a thrombosis, which can
obstruct vessels. Problems with blood composition, the pumping
action of the heart, or narrowing of blood vessels can have many consequences including
hypoxia (lack of oxygen) of the tissues supplied. The term ischemia refers to tissue that is
inadequately perfused with blood, and infarction refers to tissue death (necrosis), which can
occur when the blood supply has been blocked (or is very inadequate).===Hematological disorders===Anemia
Insufficient red cell mass (anemia) can be the result of bleeding, blood disorders like
thalassemia, or nutritional deficiencies, and may require one or more blood transfusions. Anemia can also be due to a genetic disorder
in which the red blood cells simply do not function effectively. Anemia can be confirmed by a blood test if
the hemoglobin value is less than 13.5 gm/dl in men or less than 12.0 gm/dl in women. Several countries have blood banks to fill
the demand for transfusable blood. A person receiving a blood transfusion must
have a blood type compatible with that of the donor. Sickle-cell anemia
Disorders of cell proliferation Leukemia is a group of cancers of the blood-forming
tissues and cells. Non-cancerous overproduction of red cells
(polycythemia vera) or platelets (essential thrombocytosis) may be premalignant. Myelodysplastic syndromes involve ineffective
production of one or more cell lines. Disorders of coagulation
Hemophilia is a genetic illness that causes dysfunction in one of the blood’s clotting
mechanisms. This can allow otherwise inconsequential wounds
to be life-threatening, but more commonly results in hemarthrosis, or bleeding into
joint spaces, which can be crippling. Ineffective or insufficient platelets can
also result in coagulopathy (bleeding disorders). Hypercoagulable state (thrombophilia) results
from defects in regulation of platelet or clotting factor function, and can cause thrombosis. Infectious disorders of blood
Blood is an important vector of infection. HIV, the virus that causes AIDS, is transmitted
through contact with blood, semen or other body secretions of an infected person. Hepatitis B and C are transmitted primarily
through blood contact. Owing to blood-borne infections, bloodstained
objects are treated as a biohazard. Bacterial infection of the blood is bacteremia
or sepsis. Viral Infection is viremia. Malaria and trypanosomiasis are blood-borne
parasitic infections.===Carbon monoxide poisoning===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.==Medical treatments=====
Blood products===Blood for transfusion is obtained from human
donors by blood donation and stored in a blood bank. There are many different blood types in humans,
the ABO blood group system, and the Rhesus blood group system being the most important. Transfusion of blood of an incompatible blood
group may cause severe, often fatal, complications, so crossmatching is done to ensure that a
compatible blood product is transfused. Other blood products administered intravenously
are platelets, blood plasma, cryoprecipitate, and specific coagulation factor concentrates.===Intravenous administration===
Many forms of medication (from antibiotics to chemotherapy) 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, CaCl2 etc.) 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.===Bloodletting===In modern evidence-based medicine, bloodletting
is used in management of a few rare diseases, including hemochromatosis and polycythemia. However, bloodletting and leeching were common
unvalidated interventions used until the 19th century, as many diseases were incorrectly
thought to be due to an excess of blood, according to Hippocratic medicine.==Etymology==According to the Oxford English Dictionary,
the word “blood” dates to the oldest English, circa 1000 CE. The word is derived from Middle English, which
is derived from the Old English word blōd, which is akin to the Old High German word
bluot, meaning blood. The modern German word is (das) Blut.==History=====
Classical Greek medicine===Fåhræus (a Swedish physician who devised
the erythrocyte sedimentation rate) suggested that the Ancient Greek system of humorism,
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
The ABO blood group system was discovered in the year 1900 by Karl Landsteiner. Jan Janský is 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 first blood transfusion was performed
that used the ABO system to predict compatibility. The first non-direct transfusion was performed
on March 27, 1914. The Rhesus factor was discovered in 1937.==Cultural and religious beliefs==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 to bloodlines, and sayings
such as “blood is thicker than water” and “bad blood”, as well as “Blood brother”. Blood is given particular emphasis in the
Jewish and Christian religions, because Leviticus 17:11 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.===Indigenous Australians===
In many indigenous Australian Aboriginal peoples’ traditions, ochre (particularly red) and blood,
both high in iron content and considered Maban, are applied to the bodies of dancers for ritual. As Lawlor states:
In many Aboriginal rituals and ceremonies, red ochre is rubbed all over the naked bodies
of the dancers. In secret, sacred male ceremonies, blood extracted
from the veins of the participant’s arms is exchanged and rubbed on their bodies. Red ochre is used in similar ways in less-secret
ceremonies. Blood is also used to fasten the feathers
of birds onto people’s bodies. Bird feathers contain a protein that is highly
magnetically sensitive. Lawlor comments that blood employed in this
fashion is held by these peoples to attune the dancers to the invisible energetic realm
of the Dreamtime. Lawlor then connects these invisible energetic
realms and magnetic fields, because iron is magnetic.===European paganism===
Among the Germanic tribes, blood was used during their sacrifices; the Blóts. 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 called blóedsian
in Old English, and the terminology was borrowed by the Roman Catholic Church becoming to bless
and blessing. The Hittite word for blood, ishar was a cognate
to words for “oath” and “bond”, see Ishara. The Ancient Greeks believed that the blood
of the gods, ichor, was a substance that was poisonous to mortals. As a relic of Germanic Law, the cruentation,
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.===Christianity===
In Genesis 9:4, God prohibited Noah and his sons from eating blood (see Noahide Law). This command continued to be observed by the
Eastern Orthodox. 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 the Council of Jerusalem, the apostles
prohibited 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 the atonement
of 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 the Assyrian Church of the East teach that,
when consecrated, the Eucharistic wine actually becomes the blood of Jesus for worshippers
to drink. Thus in the consecrated wine, Jesus becomes
spiritually and physically present. This teaching is rooted in the Last Supper,
as written in the four gospels of the Bible, in which Jesus stated to his disciples that
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 a Wesleyan or Presbyterian lineage, teach that the wine is no more than a symbol of
the blood of Christ, who is spiritually but not physically present. Lutheran theology teaches that the body and
blood is present together “in, with, and under” the bread and wine of the Eucharistic feast.===Judaism===
In Judaism, animal blood may not be consumed even in the smallest quantity (Leviticus 3:17
and elsewhere); this is reflected in Jewish dietary laws (Kashrut). Blood is purged from meat by rinsing and soaking
in water (to loosen clots), salting and 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 of
fowl and game after slaughtering (Leviticus 17:13); the reason given by the Torah is:
“Because the life of the animal is [in] its blood” (ibid 17:14). In relation to human beings, Kabbalah expounds
on this verse that the animal soul of 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 of food containing blood is forbidden by Islamic dietary laws. This is derived from the statement in the
Qur’an, sura Al-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 to menstruation,
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.===Jehovah’s Witnesses===Based on their interpretation of scriptures
such as Acts 15:28, 29 (“Keep abstaining…from blood.”), many Jehovah’s Witnesses neither
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.===East Asian culture===
In south East Asian popular culture, it is often said that if a man’s nose produces a
small flow of blood, he is experiencing sexual desire. This often appears in Chinese-language and
Hong Kong films as well as in Japanese and Korean culture parodied in anime, manga, and
drama. Characters, mostly males, will often be shown
with a nosebleed if they have just seen someone nude or in little clothing, or if they have
had an erotic thought or fantasy; this is based on the idea that a male’s blood pressure
will spike dramatically when aroused.===Vampire legends===Vampires are 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 achieves damnation and immortality
by drinking the blood of others, originates from Eastern European folklore. Ticks, leeches, female mosquitoes, 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
are new world creatures discovered well after the origins of the European myths.==Applications=====In the applied sciences===
Blood residue can help forensic investigators identify weapons, reconstruct a criminal action,
and link suspects to the crime. Through bloodstain pattern analysis, forensic
information can also be gained from the spatial distribution of bloodstains. Blood residue analysis is also a technique
used in archeology.===In art===
Blood is one of the body fluids that has been used in art. In particular, the performances of Viennese
Actionist Hermann Nitsch, Istvan Kantor, Franko B, Lennie Lee, Ron Athey, Yang Zhichao, Lucas
Abela and Kira O’ Reilly, along with the photography of Andres Serrano, have incorporated blood
as a prominent visual element. Marc Quinn has made sculptures using frozen
blood, including a cast of his own head made using his own blood.===In genealogy and family history===
The term blood is used in genealogical circles to refer to one’s ancestry, origins, and ethnic
background as in the word bloodline. Other terms where blood is used in a family
history sense are blue-blood, royal blood, mixed-blood and blood relative.==See also

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