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What exactly is blood?

What exactly is blood?


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There is a scripture (Leviticus 17:11) in the bible that states:

For the life of the flesh is in the blood and I have given it to you upon the altar to make an atonement for your souls

The blood (and body parts) of animals such as goats, sheep, rams, oxen, bulls, and doves were used to perform sacrificial rituals as a means of purification and cleansing. Within this particular verse, the English word life is used to convey/translate the Hebraic word Nephesh, which can sum up to mean the "essence" or the "substance" of the person or animal.

The reason I am asking this question in the Biology StackExchange is that I wanted to get an understanding of what exactly blood is from a scientific perspective.

What exactly is blood (as pertaining to vertebrates)? What does it consist of? How different is human blood compared to that of animals (specifically the Bovidae and Columbidae family)? Thank you


Blood is a body fluid in humans and other animals such as goats, sheep, rams, oxen, bulls, doves, etc. that is pushed through the organism by the heart, which delivers necessary "essence" or "substance" such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells.

Blood is made up of blood plasma and various cells - red blood cells, white blood cells and platelets. Platelets help blood to clot. Hemoglobin is in red blood cells. White blood cells help fight infections and heal wounds.

Learn more about blood from Wikipedia, Simple Wikipedia, Khan Academy


Blood consists of several elements. The major components of blood include plasma, red blood cells, white blood cells, and platelets.

  • Plasma: This major constituent of blood comprises about 55 percent of blood volume. It consists of water with several different substances dissolved within. Plasma contains salts, proteins, and blood cells. Plasma also transports nutrients, sugars, fats, hormones, gases, and waste material contained within blood.
  • Red Blood Cells (erythrocytes): These cells determine blood type and are the most abundant cell type in the blood. Red blood cells have what is known as a biconcave shape. Both sides of the cell's surface curve inward like the interior of a sphere. This flexible disc shape helps to increase the surface area-to-volume ratio of these extremely small cells. Red blood cells do not have a nucleus, but they do contain millions of hemoglobin molecules. These iron-containing proteins bind oxygen molecules obtained in the lungs and transport them to various parts of the body. After depositing oxygen to tissue and organ cells, red blood cells pick up carbon dioxide (CO2) for transportation to the lungs where the CO2 is expelled from the body.
  • White Blood Cells (leukocytes): These cells play an important role in the immune system and lymphatic system by defending the body against infection. These cells locate, destroy, and remove pathogens and foreign matter from the body. There are several different types of white blood cells, each with different functions. Examples include lymphocytes, monocytes, neutrophils, basophils, and eosinophils.
  • Platelets (thrombocytes): These cell components are formed from pieces of cells found in the bone marrow called megakaryocytes. Fragments of the megakaryocytes circulate through the bloodstream and play a major role in clotting. When platelets encounter an injured blood vessel, they clump together to block the opening in the vessel.

Antigen

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Antigen, substance that is capable of stimulating an immune response, specifically activating lymphocytes, which are the body’s infection-fighting white blood cells. In general, two main divisions of antigens are recognized: foreign antigens (or heteroantigens) and autoantigens (or self-antigens). Foreign antigens originate from outside the body. Examples include parts of or substances produced by viruses or microorganisms (such as bacteria and protozoa), as well as substances in snake venom, certain proteins in foods, and components of serum and red blood cells from other individuals. Autoantigens, on the other hand, originate within the body. Normally, the body is able to distinguish self from nonself, but in persons with autoimmune disorders, normal bodily substances provoke an immune response, leading to the generation of autoantibodies. An antigen that induces an immune response—i.e., stimulates the lymphocytes to produce antibody or to attack the antigen directly—is called an immunogen.

On the surface of antigens are regions, called antigenic determinants, that fit and bind to receptor molecules of complementary structure on the surface of the lymphocytes. The binding of the lymphocytes’ receptors to the antigens’ surface molecules stimulates the lymphocytes to multiply and to initiate an immune response—including the production of antibody, the activation of cytotoxic cells, or both—against the antigen. The amount of antibody formed in response to stimulation depends on the kind and amount of antigen involved, the route of entry to the body, and individual characteristics of the host.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Adam Augustyn, Managing Editor, Reference Content.


What Is Diastolic Blood Pressure?

The diastolic blood pressure is the pressure the blood exerts within the arteries in between heartbeats, that is, when the heart is not actively ejecting blood into the arteries.

After the heart is finished contracting, the cardiac ventricles relax momentarily so that they can be refilled with blood, in preparation for the next contraction. This period of ventricular relaxation is called “diastole,” and the blood pressure during diastole is called the diastolic blood pressure.

A “normal” diastolic blood pressure during quiet rest is 80 mmHg or below.   In hypertension, the diastolic blood pressure is often increased during quiet rest.

Diastolic hypotension (when the diastolic blood pressure is low) may be seen with dehydration   or with bleeding episodes, or if the arteries become abnormally dilated.


What is a normal blood pressure?

Normal blood pressure is vital to life. Without the pressure that forces our blood to flow around the circulatory system, no oxygen or nutrients would be delivered through our arteries to the tissues and organs.

However, blood pressure can become dangerously high, and it can also get too low.

In this article, we will discuss what blood pressure is, how it is measured, and what the measurements mean for our health.

Share on Pinterest Blood pressure is what allows oxygen and nutrients to move through our circulatory systems.

Blood pressure is the force that moves blood through our circulatory system.

It is an important force because oxygen and nutrients would not be pushed around our circulatory system to nourish tissues and organs without blood pressure.

Blood pressure is also vital because it delivers white blood cells and antibodies for immunity, and hormones such as insulin.

Just as important as providing oxygen and nutrients, the fresh blood that gets delivered is able to pick up the toxic waste products of metabolism, including the carbon dioxide we exhale with every breath, and the toxins we clear through our liver and kidneys.

Blood itself carries a number of other properties, including its temperature. It also carries one of our defenses against tissue damage, the clotting platelets that prevent blood loss following injury.

But what exactly is it that causes blood to exert a pressure in our arteries? Part of the answer is simple – the heart creates blood pressure by forcing out blood when it contracts with every heartbeat. Blood pressure, however, cannot be created solely by the pumping heart.

The National Institutes of Health cite normal blood pressure to be below 120 mm Hg systolic and 80 mm Hg diastolic.

However, blood pressure changes naturally, a fact that cardiologists explored while writing about blood-pressure variability in Nature in March 2013:

“ Blood pressure is characterized by marked short-term fluctuations occurring within a 24-hour period (beat-to-beat, minute-to-minute, hour-to-hour, and day-to-night changes) and also by long-term fluctuations occurring over more prolonged periods of time (days, weeks, months, seasons, and even years).”

The guidelines state that for blood pressures above a figure of 115/75 mm Hg, every rise of 20/10 mm Hg doubles the risk of cardiovascular disease.

The overall guidelines for high blood pressure received an update in November 2017. They allow for earlier intervention.

Since 2017, the American Heart Association (AHA) has advised that people with high blood pressure should receive treatment at 130/80 mm Hg rather than 140/90 mm Hg.

They also removed the “prehypertension” category between 120-139/80-89 mm Hg. A blood pressure reading of 140/90 mm Hg now qualifies as stage II hypertension and not stage I, as it used to be.

This category now forms two separate ranges:

  • elevated blood pressure, from 120-129/less than 80 mm Hg
  • stage I hypertension, from 130-139/80-89 mm Hg

In these new guidelines, the AHA also advises that doctors should only prescribe medication in cases of a previous heart attack or stroke, or in the presence of risk factors for these conditions, such as age, a diabetes mellitus diagnosis, or chronic kidney disease.

Treatment at the earlier stages should instead come mainly through lifestyle changes.

Our circulation is similar to a highly sophisticated form of plumbing – blood has ‘flow’ and arteries are ‘pipes.’ A basic law of physics gives rise to our blood flow, and this law also applies in a garden hose pipe.

Blood flows through our body because of a difference in pressure.

Our blood pressure is highest at the start of its journey from our heart – when it enters the aorta – and it is lowest at the end of its journey along progressively smaller branches of arteries. That pressure difference is what causes blood to flow around our bodies.

Arteries affect blood pressure in a similar way to the physical properties of a garden hose pipe affecting water pressure. Constricting the pipe increases pressure at the point of constriction.

Without the elastic nature of the artery walls, for example, the pressure of the blood would fall away more quickly as it is pumped from the heart.

While the heart creates the maximum pressure, the properties of the arteries are just as important to maintaining it and allowing blood to flow throughout the body.

The condition of the arteries affects blood pressure and flow, and narrowing of the arteries can eventually block the supply altogether, leading to dangerous conditions including stroke and heart attack.

The device used to measure blood pressure is a sphygmomanometer, it consists of a rubber armband – the cuff that is inflated by hand or machine pump.

Once the cuff is inflated enough to stop the pulse, a reading is taken , either electronically or on an analogue dial.

The reading is expressed in terms of the pressure it takes to move mercury round a tube against gravity. This is the reason for pressure being measured using the unit millimeters of mercury, abbreviated to mm Hg.

A stethoscope identifies the precise point when the pulse sound returns and the pressure of the cuff is slowly released. Using the stethoscope enables the person measuring the blood pressure to listen out for two specific points.

Blood pressure readings consist of two figures – the systolic pressure first and the diastolic pressure second. The reading is given as, for example, 140 over 90 mm Hg.

The systolic pressure is the higher figure caused by the heart’s contraction, while the diastolic number is the lower pressure in the arteries, during the brief ‘resting’ period between heartbeats.

The guidelines for doctors list the following measures patients can take to help keep a healthy blood pressure:

  • Keep a healthy body weight.
  • Eat a diet rich in fruits, vegetables, and low-fat dairy products.
  • Cut down on sodium, or salt, in the diet.
  • Take regular aerobic exercise, such as brisk walking, for at least 30 minutes a day, most days of the week.
  • Moderate alcohol intake. Men should drink fewer than two alcoholic beverages a day for men. Women and men with a lower body weight should consume a maximum of one alcohol drink a day.

Taking these steps can reduce the risk of health problems further down the line.


What does it mean to be genetically Jewish?

W hen my parents sent their saliva away to a genetic testing company late last year and were informed via email a few weeks later that they are both “100% Ashkenazi Jewish”, it struck me as slightly odd. Most people I know who have done DNA tests received ancestry results that correspond to geographical areas – Chinese, British, West African. Jewish, by comparison, is typically parsed as a religious or cultural identity. I wondered how this was traceable in my parents’ DNA.

After arriving in eastern Europe around a millennium ago, the company’s website explained, Jewish communities remained segregated, by force and by custom, mixing only occasionally with local populations. Isolation slowly narrowed the gene pool, which now gives modern Jews of European descent, like my family, a set of identifiable genetic variations that set them apart from other European populations at a microscopic level.

This genetic explanation of my Ashkenazi Jewish ancestry came as no surprise. According to family lore, my forebears lived in small towns and villages in eastern Europe for at least a few hundred years, where they kept their traditions and married within the community, up until the Holocaust, when they were either murdered or dispersed.

But still, there was something disconcerting about our Jewishness being “confirmed” by a biological test. After all, the reason my grandparents had to leave the towns and villages of their ancestors was because of ethno-nationalism emboldened by a racialized conception of Jewishness as something that exists “in the blood”.

The raw memory of this racism made any suggestion of Jewish ethnicity slightly taboo in my family. If I ever mentioned that someone “looked Jewish” my grandmother would respond, “Oh really? And what exactly does a Jew look like?” Yet evidently, this wariness of ethnic categorization didn’t stop my parents from sending swab samples from the inside of their cheeks off to a direct-to-consumer genetic testing company. The idea of having an ancient identity “confirmed” by modern science was too alluring.

Not that they’re alone. As of the beginning of this year, more than 26 million people have taken at-home DNA tests. For most, like my parents, genetic identity is assimilated into an existing life story with relative ease, while for others, the test can unearth family secrets or capsize personal narratives around ethnic heritage.

But as these genetic databases grow, genetic identity is reshaping not only how we understand ourselves, but how we can be identified by others. In the past year, law enforcement has become increasingly adept at using genetic data to solve cold cases a recent study shows that even if you haven’t taken a test, chances are you can be identified by authorities via genealogical sleuthing.

What is perhaps more concerning, though, is how authorities around the world are also beginning to use DNA to not only identify individuals, but to categorize and discriminate against entire groups of people.

In February of this year, the Israeli newspaper Haaretz, reported that the Chief Rabbinate of Israel, the peak religious authority in the country, had been requesting DNA tests to confirm Jewishness before issuing some marriage licenses.

In Israel, matrimonial law is religious, not civil. Jews can marry Jews, but intermarriage with Muslims or Christians is legally unacknowledged. This means that when a Jewish couple want to tie the knot, they are required by law to prove their Jewishness to the Rabbinate according to Orthodox tradition, which defines Jewish ancestry as being passed down through the mother.

While for most Israeli Jews this simply involves handing over their mother’s birth or marriage certificate, for many recent immigrants to Israel, who often come from communities where being Jewish is defined differently or documentation is scarce, producing evidence that satisfies the Rabbinate’s standard of proof can be impossible.

In the past, confirming Jewishness in the absence of documentation has involved contacting rabbis from the countries where people originate or tracking genealogical records back to prove religious continuity along the matrilineal line. But as was reported in Haaretz, and later confirmed by David Lau, the Ashkenazi chief rabbi of Israel, in the past year, the rabbis have been requesting that some people undergo a DNA test to verify their claim before being allowed to marry.

For many Israelis, news that the rabbinical judges were turning to DNA testing was shocking, but for Seth Farber, an American-born Orthodox rabbi, it came as no surprise. Farber, who has been living in Israel since the 1990s, is the director of Itim, the Jewish Life Information Center, an organization that helps Israeli Jews navigate state-administered matters of Jewish life, like marriage and conversion. In the past year, the organization has seen up to 50 cases where families have been asked to undergo DNA tests to certify their Jewishness.

Those being asked to take these tests, Farber told me, are mostly Russian-speaking Israelis, members of an almost 1 million-strong immigrant community who began moving to Israel from countries of the former Soviet Union in the 1990s. Due to the fact that Jewish life was forcefully suppressed during the Soviet era, many members of this community lack the necessary documentation to prove Jewishness through matrilineal descent. This means that although most self-identify as Jewish, hundreds of thousands are not considered so by the Rabbinate, and routinely have their Jewish status challenged when seeking religious services, including marriage.

For almost two decades, Farber and his colleagues have advocated for this immigrant community in the face of what they see as targeted discrimination. In cases of marriage, Farber acts as a type of rabbinical lawyer, pulling together documentation and making a case for his clients in front of a board of rabbinical judges. He fears that DNA testing will place even more power in the hands of the Rabbinate and further marginalize the Russian-speaking community. “It’s as if the rabbis have become technocrats,” he told me. “They are using genetics to give validity to their discriminatory practices.”

Despite public outrage and protests in central Tel Aviv, the Rabbinate have not indicated any intention of ending DNA testing, and reports continue to circulate in the Israeli media of how the test is being used. One woman allegedly had to ask her mother and aunt for genetic material to prove that she was not adopted. Another man was asked to have his grandmother, sick with dementia, take a test.

A protest against DNA testing in Tel Aviv. Photograph: Boris Shindler

Boris Shindler, a political activist and active member of the Russian-speaking community, told me that he believes that the full extent of the practice remains unknown, because many of those who have been tested are unwilling to share their stories publicly out of a sense of shame. “I was approached by someone who was married in a Jewish ceremony maybe 15, 20 years ago, who recently received an official demand saying if you want to continue to be Jewish, we’d like you to do a DNA test,” Shindler said. “They said if she doesn’t do it then she has to sign papers saying she is not Jewish. But she is too humiliated to go to the press with this.”

What offends Shindler most is that the technique is being used to single out his community, which he sees as part of a broader stigmatization of Russian-speaking immigrants in Israeli society as unassimilated outsiders and second-class citizens. “It is sad because in the Soviet Union we were persecuted for being Jewish and now in Israel we’re being discriminated against for not being Jewish enough,” he said.

As well as being deeply humiliating, Shindler told me that there is confusion around what being genetically Jewish means. “How do they decide when someone becomes Jewish,” he asked. “If I have 51% Jewish DNA does that mean I’m Jewish, but if I’m 49% I’m not?”

But according to Yosef Carmel, an Orthodox rabbi and co-head of Eretz Hemdah, a Jerusalem-based institute that trains rabbinical judges for the Rabbinate, this is a misunderstanding of how the DNA testing is being used. He explained that the Rabbinate are not using a generalized Jewish ancestry test, but one that screens for a specific variant on the mitochondrial DNA – DNA that is passed down through the mother – that can be found almost exclusively in Ashkenazi Jews.

A number of years ago Carmel consulted genetic experts who informed him that if someone bears this specific mitochondrial DNA marker, there is a 90 to 99% chance that this person is of Ashkenazi ancestry. This was enough to convince him to pass a religious ruling in 2017 that states that this specific DNA test can be used to confirm Jewishness if all other avenues have been exhausted, which now constitutes the theological justification for the genetic testing.

For David Goldstein, professor of medical research in genetics at Columbia University whose 2008 book, Jacob’s Legacy: A Genetic View of Jewish History, outlines a decade’s worth of research into Jewish population genetics, translating scientific insights about small genetic variants in the DNA to normative judgments about religious or ethnic identity is not only problematic, but misunderstands what the science actually signals.

“When we say that there is a signal of Jewish ancestry, it’s a highly specific statistical analysis done over a population,” he said. “To think that you can use these type of analyses to make any substantive claims about politics or religion or questions of identity, I think that it’s frankly ridiculous.”

But others would disagree. As DNA sequencing becomes more sophisticated, the ability to identify genetic differences between human populations has improved. Geneticists can now locate variations in the DNA so acutely as to differentiate populations living on opposite sides of a mountain range.

In recent years, a number of high-profile commentators have appropriated these scientific insights to push the idea that genetics can determine who we are socially, none more controversially than the former New York Times science writer Nicholas Wade. In his 2014 book, A Troublesome Inheritance: Genes, Race and Human History, Wade argues that genetic differences in human populations manifest in predictable social differences between those groups.

His book was strongly denounced by almost all prominent researchers in the field as a shoddy incarnation of race science, but the idea that our DNA can determine who we are in some social sense has also crept into more mainstream perspectives.

In an op-ed published in the New York Times last year, the Harvard geneticist David Reich argued that although genetics does not substantiate any racist stereotypes, differences in genetic ancestry do correlate to many of today’s racial constructs. “I have deep sympathy for the concern that genetic discoveries could be misused to justify racism,” he wrote. “But as a geneticist I also know that it is simply no longer possible to ignore average genetic differences among ‘races’.”

Reich’s op-ed was shared widely and drew condemnation from other geneticists and social science researchers.

In an open letter to Buzzfeed, a group of 67 experts also criticized Reich’s careless communication of his ideas. The signatories worried that imprecise language within such a fraught field of research would make the insights of population genetics more susceptible to being “misunderstood and misinterpreted”, lending scientific validity to racist ideology and ethno-nationalist politics.

And indeed, this already appears to be happening. In the United States, white nationalists have channeled the ideals of racial purity into an obsession with the reliability of direct-to-consumer DNA testing. In Greece, the neo-fascist Golden Dawn party regularly draw on studies on the origins of Greek DNA to “prove” 4,000 years of racial continuity and ethnic supremacy.

Most concerning is how the conflation of genetics and racial identity is being mobilized politically. In Australia, the far-right One Nation party recently suggested that First Nations people be given DNA tests to “prove” how Indigenous they are before receiving government benefits. In February, the New York Times reported that authorities in China are using DNA testing to determine whether someone is of Uighur ancestry, as part of a broader campaign of surveillance and oppression against the Muslim minority.

While DNA testing in Israel is still limited to proving Jewishness in relation to religious life, it comes at a time when the intersections of ethnic, political and religious identity are becoming increasingly blurry. Just last year, Benjamin Netanyahu’s government passed the Nation State law, which codified that the right to national self-determination in the country is “unique to the Jewish people”.

Shlomo Sand, an Israeli historian who has written extensively on the politics of Jewish population genetics, worries that if DNA testing is normalized by the Rabbinate, it could be used to confirm citizenship in the future. “Israeli society is becoming more of a closed, ethno-centric society,” he said. “I am worried that people will start to use this genetic testing to build this political national identity.”

For Sand, there is a particularly dark irony that this type of genetic discrimination is being weaponized by Jews against other Jews. “I am the descendant of Holocaust survivors, people who suffered because of biological and essentialist attitudes to human groups,” he told me. “When I hear stories of people using DNA to prove that you are a Jew, or French, or Greek, or Finnish, I feel like the Nazis lost the war, but they won the victory of an ideology of essentialist identity through the blood.”

But for Seth Farber, the problem with a DNA test for Jewishness runs deeper than politics it contravenes what he believes to be the essence of Jewish identity. There is a specific principle in Jewish law, he told me, that instructs rabbis not to undermine someone’s self-declared religious identity if that person has been accepted by a Jewish community. The central principle is that when it comes to Jewish identity, the most important determinants are social – trust, kinship, commitment – not biological. “Our tradition has always been that if someone lives among us and partakes in communal and religious life, then they are one of us,” Farber said. “Just because we have 23andMe doesn’t mean that we should abandon this. That would be an unwarranted and radical reinterpretation of Jewish law.”

As I was reporting this story, it often struck me as oxymoronic that an institution like the Rabbinate would embrace new technology to uphold an ancient identity. It seemed to contradict the very premise of Orthodoxy, which, by definition, is supposed to rigidly maintain tradition in the face of all that is new and unknown.

But Jessica Mozersky, assistant professor of medicine at Washington University in St Louis, explained that part of the reason why the Rabbinate might be comfortable with using DNA to confirm Jewishness is because of an existing familiarity with genetic testing in the community to screen for rare genetic conditions. “Because Ashkenazi communities have a history of marrying in, they have this high risk for certain heritable diseases and have established genetic screening programs,” she explained. “So this has made it less fraught and problematic to talk about Jewish genetics in Ashkenazi communities.”

In fact, the Orthodox Jewish community is so comfortable with the idea of genetic identity that they have even put together their own international genetic database called Dor Yeshorim, which acts as both a dating service and public health initiative. When two members of the community are being set up for marriage, Mozersky explained, the matchmaker will check whether or not they are genetically compatible on the DNA database. “This means that the notion of genetics as a part of identity is deeply interwoven in many ways with communal life,” she said.

This is something I could identify with. When I was 16 and attending a Jewish day-school in Melbourne, Australia, we had what was called “mouth-swab day”. Everyone in my grade gathered on the basketball courts to provide spit samples that were sent off and screened for Tay-Sachs disease, a rare inherited disorder significantly more common among Ashkenazi Jews that eats away at the nerve cells in the brain and spinal cord. As we waited in line, we joked that this was our punishment for our ancestors marrying their cousins.

A few weeks later, after we got the results, I told my grandmother about “mouth-swab day”. I was interested in her thoughts on my newly discovered genetic identity, which seemed to connect me biologically to the world she grew up in, a world of insularity, religiosity, tradition, and trauma.

“It’s like I’ve always said,” she declared, after I told her that I wasn’t a carrier of this rare genetic mutation. “It’s important to mix the blood.”


How does blood work, and what problems occur?

Blood is a combination of plasma and cells that circulate through the entire body. It is a specialized bodily fluid that supplies essential substances around the body, such as sugars, oxygen, and hormones.

It also removes waste from the cells in the body.

Hematologists work to identify and prevent blood and bone marrow diseases, as well as studying and treating the immune system, blood clotting, and the veins and arteries.

In the United States (U.S.), blood diseases accounted for between 9,000 and 10,000 annual deaths from 1999 to 2010. This constitutes less than one percent of total deaths from disease.

  • Blood transports oxygen and nutrients around the body and removes cellular waste, among a range of other vital functions.
  • Plasma makes up 55 percent of blood content. The other 45 percent consists mainly of red blood cells and platelets.
  • Blood groups are categorized based on the antibodies and antigens in the cell. Receiving an incompatible blood donation can lead to fatal complications. , blood cancer, and clots are all potential disorders of the blood.

Blood consists of plasma, red and white blood cells, and platelets.

Plasma: This constitutes approximately 55 percent of blood fluid in humans.

Plasma is 92 percent water, and the contents of the remaining 8 percent include:

  • carbon dioxide
  • glucose
  • hormones
  • proteins
  • mineral salts
  • fats

The remaining 45 percent of the blood mainly consists of red and white blood cells and platelets. Each of these has a vital role to play in keeping the blood functioning effectively.

Red blood cells (RBCs), or erythrocytes: They are shaped like slightly indented, flattened disks and transport oxygen to and from the lungs. Hemoglobin is a protein that contains iron and retains the oxygen until its destination. The life span of an RBC is 4 months, and the body replaces them regularly. Amazingly, our body produces around 2 million blood cells every second.

The expected number of RBCs in a single drop, or microliter, of blood is 4.5 to 6.2 million in men and 4.0 to 5.2 million in women.

White blood cells, or leukocytes: White blood cells make up less than 1 percent of blood content, and they form vital defenses against disease and infection. The normal range of the number of white blood cells in a microliter of blood is between 3,700 and 10,500. Higher and lower levels of white blood cells can indicate disease.

Platelets, or thrombocytes: These interact with clotting proteins to prevent or stop bleeding. There should be between 150,000 and 400,000 platelets per microliter of blood.

RBCs, white blood cells, and platelets are produced in the bone marrow before entering the bloodstream. Plasma is mostly water that is absorbed from ingested food and drink by the intestines. Combined, these are propelled around the entire body by the heart and carried by the blood vessels.

Blood has a number of functions that are central to survival, including:

  • supplying oxygen to cells and tissues
  • providing essential nutrients to cells, such as amino acids, fatty acids, and glucose
  • removing waste materials, such as carbon dioxide, urea, and lactic acid
  • protecting the body from infection and foreign bodies through the white blood cells
  • transporting hormones from one part of the body to another, transmitting messages, and completing important processes
  • regulating acidity (pH) levels and body temperature
  • engorging parts of the body when needed, for example, a penile erection as a response to sexual arousal

Another important function of the blood is its protective action against disease. White blood cells defend the body against infections, foreign materials, and abnormal cells.

The platelets in blood enable the clotting, or coagulation, of blood. When bleeding occurs, the platelets group together to create a clot. The clot becomes a scab and stops the bleeding, as well as helping to protect the wound from infection.

Blood groups categorize blood based on the presence and absence of certain antibodies. The groupings also take into account antigens on the surface of the blood cells.

Antibodies are proteins in plasma that alert the immune system to the presence of potentially harmful foreign substances. The immune system will attack the threat of disease or infection. Antigens are protein molecules on the surface of red blood cells.

When giving or receiving organ donations or blood transfusions, the blood group of an individual becomes extremely important. Antibodies will attack new blood cells if they have an unrecognizable antigen, and this can lead to life-threatening complications. For example, anti-A antibodies will attack cells that have A antigens.

RBCs sometimes contain another antigen called RhD. This is also noted as part of the blood group. A positive blood group means that RhD is present.

Humans can have one of four main blood groups. Each of these groups can be Rhd positive or negative, forming eight main categories.

  • Group A positive or A negative: A antigens are found on the surfaces of blood cells. Anti-B antibodies are found in the plasma.
  • Group B positive or B negative: B antigens are found on the surfaces of blood cells. Anti-A antibodies are found in the plasma.
  • Group AB positive or AB negative: A and B antigens are found on the surfaces of blood cells. There are no antibodies are found in the plasma.
  • Group O positive and O negative: There are no antigens are found on the surfaces of blood cells. Both anti-B and anti-A antibodies are found in the plasma.

Group O blood can be given to people of virtually any blood type, and people with Group AB+ blood can generally receive blood from any group. Talk to your doctor to find out your blood type. If you donate blood, a doctor can also tell you your blood type.

Blood groups are important during pregnancy. If a woman has RhD negative blood, for example, but her fetus inherits RhD positive blood from the father, treatment will be needed to prevent a condition known as hemolytic disease of the newborn (HDN).

Disorders and diseases of the blood can be dangerous. They can spread rapidly during the circuit of the bloodstream around the body, and impair the many functions aided by blood.

The most common blood disorders are:

  • Anemia: This is a shortage of RBCs or hemoglobin in the blood. As a result, the cells do not transport oxygen effectively, and symptoms can include fatigue and pale skin.
  • Blood clots: These can be vital for the healing process of wounds and injuries. However, some clots coagulate inside a blood vessel and create a blockage. They can also become dislodged and move through the heart to the lungs, leading to a pulmonary embolism. Clots can be fatal.
  • Blood cancers: Leukemia, myeloma, and lymphoma are types of blood cancer. Mutated blood cells divide uncontrollably without dying at the normal point in the life cycle of a cell.

If symptoms of a blood disorder are suspected, the patient should visit a primary care physician. It is likely that they will be referred to a specialist in blood disorders, known as a hematologist.


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Blood cells

Blood is a connective tissue that flows through the body of many animals, transporting gases, nutrients, waste products and hormones around the body. Is it also important for a number of other functions such as regulating the fluid that surrounds cells, reducing fluid loss after injury, regulating body temperature and immunity defenses.

Relative to water, blood is a viscous fluid due to the amount of proteins, red blood cells and other compounds it contains. It owes its vibrant red color to haemoglobin, a protein found in the red blood cells that binds to oxygen and increases the efficiency of oxygen transport around the body.

The contents of blood can be separated into two groups one group is called the “formed elements” which is 99.9% red blood cells, but also includes white blood cells and platelets (important components of the immune system and the clotting of blood). The other half of the blood is known as plasma and contains around 92% water, plasma proteins and other solutes such as electrolytes and organic wastes.

Red blood cells

Red blood cells (RBC) are responsible for the transportation of oxygen around the body and their significance is proven by the fact that they account for almost half of the entire blood volume. They are chocked full with haemoglobin which makes up approximately 95% of the proteins found in red blood cells.

Structurally red blood cells are shaped like a doughnut without the hole. This shape creates a large surface area which helps to increase the efficiency of oxygen exchange between the blood and tissue cells. Their shape also makes it easier for them to travel through thin capillaries as they can bend more and stack together.

Another important feature of RBCs in mammals is that they don’t have a nucleus or any organelles, one of the only animal or plant cells to lack such features. There is a certain level of variation between mammal species but generally the nucleus and organelles are absent in the red blood cells.

Haemoglobin

Haemoglobin is one of the most important and common proteins in the body. It is a globular protein – shaped like a globe – and is formed from four sub-unit proteins, each with a haem group in the middle. The haem group is a molecule in the center of the protein and has an iron ion, Fe 2+ , in its center. The haem group is able to reversibly bond to oxygen which is why haemoglobin is so helpful for transporting oxygen around the body.

The Fe 2+ ion attracts oxygen but but the protein surrounding the Fe 2+ ion prevents the oxygen from bonding and becoming FeO, or rust. Changes in the shape of the protein affect how tightly or loosely oxygen binds to the haem depending how close the O2 gets to the iron within the haem molecule.

White blood cells

The white blood cells or leukocytes show a much greater variation than the red blood cells and they perform a wide range of functions, more often than not, that help boost the immune system. They differ significantly from red blood cells in that they have nuclei and other organelles and do not have any haemoglobin.

There are a number of different types of white blood cells such as neutrophils, basophils, eosinophils and lymphocytes. Each different type of white blood cell performs a different set of functions. Neutrophil cells are the most common and make up to 70% of the white blood cells. They are an important component of the inflammatory system and are the cells responsible for the formation of pus. Basophil cells release compounds, such as histamine that help the repairing process of damaged tissue.

Eosinophils are a type of cell known as phagocytes, which basically means they engulf substances, often foreign to the body, such as bacteria, but also the break down components of bodily compounds, such as dead cells. Each eosinophil has particular anti-bodies, compounds on the cells exterior that attract the cell to specific compounds, which may be found on the cells of bacteria or the break-down components of damaged tissue. Macrophage cells are large generalist phagocytes.

Lymphocytes are very specific defense cells and are crucial to the adaptive immune system of mammals and higher animals. Lymphocyte cells include T cells, B cells and Natural Killer cells.

Blood plasma

The blood plasma contain a number of important compounds such as proteins, water and electrolyes. The most common plasma proteins are the albumins which are responsible for maintaining the osmotic pressure of the blood. Without albumins the blood would be more like the consistency of water. Increasing the thickness of blood reduces the amount of fluid that enters into the bloodstream from outside the capillaries.

Globulins are the second most common protein in the blood plasma. These include the immunoglobins which are an important part of the immune system and are also important for transporting hormones and other compound around the body. Fibrinogen makes up the majority of the remaining proteins in the blood and is the compound responsible for the clotting of blood to help prevent blood loss.

Transportation of blood

Blood is transported around the body through arteries, capillaries and veins. Arteries carry the blood away from the heart, and veins carry it back. Capillaries are very fine blood vessels that transport blood through the different tissues of the body. Pressure and osmotic gradients between the capillaries and the fluid outside of the capillaries allow for the transfer of blood between the two.

When blood is pumped from the heart, the pressure within the capillaries is much greater than the external pressure and blood is forced out of the capillaries to reduce the pressure. As the blood moves through the body, the pressure gradually reduces due to the movement of blood out of the capillaries. The osmotic pressure forces fluid into the capillaries once the pressure within the capillaries is reduced.

New blood cells

Haematopoiesis is the formation of new blood cells. It begins with stem cells, known as hemocytoblasts, which have the potential to form any type of blood cell. The process occurs mostly in the bone marrow but some final differentiation can occur in the blood and tissue.

Each stem cell undergoes a number of phases, each phase producing a different precursor cell than the previous phase. The pathway that any given cell might take depends on the compounds present, such as hormones, which influence how a cell will differentiate. At the end of the process a fully differentiated red, white or thrombocyte cell is formed.

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Types of Blood Groups and their Characteristics

For any living organism to survive in this world, they require proteins, nutrients and oxygen. For transfer these substances to all parts of cells of the body their need to be some transport. Blood acts as transporter in the body. It accounts 7% of human body weight with an average density of 1060 kg/m3 for adult an average volume of blood is five liters. It is composed of plasma and different types of cells. Blood constitutes different type of corpuscles in it. They are known red blood corpuscles, leukocytes and thrombocytes. For those who want to know how many types of blood groups in human body:

Red blood cells constitute 45 % of blood plasma is about 54.3% and leukocytes of 0.7%. Colour of blood is red, it is obtained by a substance which is present in it is called hemoglobin. A blood is decided based on the presence of antigens on the surface of red blood cells. Blood types are inherited and represented by contributions from both parents. So far International Society of Blood Transfusion had recognized 35 human blood group systems. Here are the main blood group and blood type

Why Do Blood Types Differ:

Blood is made of up of red and white blood cells, plasma and proteins. The plasma has antigens floating in it which is responsible for offering immunity to the body. Antigens are of two types, A and B, which produce different antibodies to fight the disease causing germs. People with O blood group have both the antibodies. This difference in antibodies create resistance to some diseases and vulnerable to others.

Percentage Of Blood Groups In India:

As per study, the most common blood group in India is O with a 37.12% of population. The second most common blood group is B with a 32,26%, followed by A at 22.8%. AB is the least found blood in the Indian subcontinent.

Rarest Blood Type In India:

The rarest blood group is Bombay Blood group, found only in 0.01% of Indian population. It is most likely found in Mumbai locals and hence the name. Among this, the negative blood group is even more rare in occurrence than positive. It is estimated that only 15 donors are identified across India with this blood group.

Blood Groups Are Classified According To Their Antigens InTo Four:

Blood group is decided whether it is positive or negative based on the Rh factor present in it. Presence of Rh antigen on red blood cells, then that particular blood is positive, if Rh is absent then it is negative. Listed below are the blood group types and their importance.

1. Blood Group AB:

These group of people can receive blood from any group especially AB preferable. But there is no chance of donating blood for this blood group people. This group of people are called are as universal acceptors or recipients.

2. Blood Group AB+:

Blood group AB+ is rare group worldwide. It has prevalence of only 4%. Blood group can improve their blood by taking diet like meat, diary, sea food, grains, nuts, fat, fruits and vegetables. As AB positive is universal acceptor all groups of blood can be transfused.

3. Blood Group AB-:

Only 1% of donor populations are available with AB negative blood. It is more required for men for manufacture of plasma. Same diet of AB +ve is followed for AB –ve also. AB- can receive blood from O negative, A negative, B negative and AB negative.

4. Blood Group A:

If the individuals have antigen A on surface of red blood cells then that is characterized as blood group A. This group has serum Igm antibodies against B antigen. These people can donate blood to only to people having blood group A and AB. Diet for blood group A has to follow is a meat free diet which is nothing but they must be complete vegetarian. They have to take beans, legumes, fruits, vegetables, whole grains which are organically fresh. This group has sensitive immune system.

5. Blood Group A+:

A positive is second most blood groups where patients needs a lot. They can receive blood from A positive, A negative, O positive and O negative. Approximately one among three constitutes 35.7 % of this group.

6. Blood Group A-:

In the world only 6.3 % of people have this group. It is rare group. These can receive blood from A negative and O negative only.

7. Blood Group B:

The persons who are possessing antigen B on red blood cells are grouped under blood group B. This group has serum Igm antibodies against A antigen. They receive blood from group B or group O. They can donate to individuals for group B or group AB. They must be herbivores and can avoid chicken, peanuts, sesame seeds, tomatoes, lentils, wheat, corn and buckwheat.

8. Blood Group B+:

B positive is third donor in the world. One among 12 individuals has B positive blood on an average of 8.5% population.

9. Blood Group B-:

This is the rare blood group and unique. On conduction of survey it is known that only one among 67 people has B negative blood group on an average of 1.5%.

10. Blood Group O:

Blood group O is termed as blood group zero in some countries. This group does not have antigen A and antigen B on red blood cells. Even blood serum does not contain antibodies A and B also. So group O can receive blood from only people who are having blood group O. This group people can donate blood to all people of other groups as it never contains antigens and antibodies. Therefore blood group O is called as universal donors. Since blood group O is compatible to all groups.

Diet for individuals who are having blood group O to be followed is high protein diet. It includes lean meat, fish, poultry, and vegetables, lightly of grains, dairy products and beans.

11. Blood Group O +:

O positive is donor. It is most common blood needed by all patients in need. On an average one among three has 37.4 % of blood group O. O positive can only donate to O group people only.

12. Blood Group O-:

O negative is called as universal donor. It can be transfused to all groups of blood. In the world only 6.6% of people have O negative blood. It is heard that O negative are medical helicopters for patients in trauma or in serious condition. One among 15 has O negative blood. If a person of O negative is in need of blood also again O negative donor must only donate the blood.

Not only blood groups but also plasma has compatibility. So in this manner blood is classified into groups. Since some antigens of the patient triggers immune system to attack transfused blood, it is safer to transfuse a blood which is suitable. So it is the duty of one’s individuality to donate blood to the needed when there is need. For every three months human body reproduces new red blood cells. Make a habit of giving blood yearly twice.


Interpreting Results

A high anion gap means you have more acid in your blood than normal. A low anion gap means you have a lower amount of acid in your blood than normal, but this result is uncommon and usually due to a lab error.

Although there are differences between laboratories and assays, the normal anion gap has traditionally been set between 8 mEq/L to 12 mEq/L, but there is a wide range of normal values—often 8 to 10 mEq/L—thus an increase in anion concentration can be present in the absence of an increased anion gap.  

What to Ask Your Doctor

A low or high anion gap does not necessarily mean that you have a serious health problem. The normal range varies from person to person, so make sure you ask your doctor to interpret the results of the test for you.


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