What Is Blood?

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What is blood made of?

There’s about 1.2-1.5 gallons (4.5-5.5 liters) of it flowing through your body. Wouldn’t it be nice to know what’s in it? Blood is a colloidal suspension of platelets, plasma, white and red blood cells. It is a solution, colloid, and suspension all in one. Compounds like salt are fully dissolved in it (solution), macromolecules like proteins are suspended in it (colloid), and when spun in a centrifuge, it separates into layers (suspension). Besides the plasma, all of blood’s constituents are formed in the bone marrow of the vertebrae, ribs, hips, skull, and sternum, according to OneBlood. Chemically, blood mostly consists of hydrogen, oxygen, chlorine, sodium, potassium, magnesium, calcium, and carbon.

  • Plasma: This is the fluid portion of the blood that allows it to travel in the body and deliver water and nutrients to tissues. Blood’s constituents are suspended in plasma, accounting for approximately 55% of blood’s volume. It’s about 92% water, 7% proteins, and 1% sugars, fats, hormones, salts, and vitamins.
  • Red cells: These cells contain hemoglobin, a protein allowing the cells to capture and deliver oxygen. When it deposits oxygen, it will pick up carbon dioxide and bring it to the lungs to be exhaled. About 40-45% of blood is made of these cells.
  • White cells: These cells fight off infection in the body. They are transported through the bloodstream, but can leave it to fight microbes in tissues. About 1% of your blood is made of white blood cells.
  • Platelets: Platelets are responsible for blood clotting. They interact with certain proteins to stop or prevent bleeding.

What does blood do?

  • Blood supplies water, oxygen, and nutrients to tissues and cells.
  • While it supplies oxygen, it removes urea, carbon dioxide, and lactic acid.
  • Platelets aid in closing wounds by coagulating blood.
  • White blood cells fight infection.
  • It regulates pH levels in the body.
  • Hormones are transported through it.
  • Temperature regulation.

What are blood types?

Blood TypeA antigen on red cellsB antigen on red cellsA antibody in plasmaB antibody in plasma
AYesNoNoYes
BNoYesYesNo
ABYesYesNoNo
ONoNoYesYes

There are four blood types: A, B, AB, and O. Each type can be positive or negative, based on its Rhesus factor. What defines a blood type is the antigen present on one’s red blood cells and the antibodies present in the blood’s plasma. These two antigens are labeled as A and B antigens. The Rhesus, or Rh, factor is the third antigen. It is used to denote blood as positive (containing it) or negative (not containing it). The compatibility chart above refers to which types of blood can be donated and received depending on type. As for the Rh factor, those with Rh+ blood can receive Rh+ and Rh- blood; those with Rh- blood can only accept other Rh- blood.

So why can’t, for example, someone with B type blood accept A type? The table above lists which antigens and antibodies are present in the different blood types (independent of Rh factor). To simplify, Rh factors are ignored for a moment. If A type blood is transfused into someone with B type blood, its B antibodies will fight against type B’s B antigens. The A antibodies in B blood will also fight against the A antigens in the type A blood. This is why AB (AB+) is the universal receiver: it has no antibodies to fight A or B antigens. This is also why O (O-) is the universal donor: it has no antigens for other blood types’ antibodies to attack, but it can only receive O blood since it has both antibodies.

Rh factor and pregnancy

Blood types are passed down through genes. A fetus can inherit the Rh gene from it’s father, potentially giving the fetus and Rh factor different from the mother’s. The incompatibility occurs when the mother is Rh- and the fetus is Rh+. This becomes a problem if the fetus’s blood and the mother’s blood come into contact. Blood contact can occur during pregnancy, labor, and birth. This usually doesn’t happen during the first pregnancy because the mother has not become Rh sensitized – developed Rh antibodies.

If the mother becomes pregnant again and the second child is Rh+ as well, she will have developed enough Rh antibodies to potentially pose a problem. Hemolytic anemia could occur where red blood cells are destroyed more quickly than the body can replace them. Rh sensitization can be prevented by being given a shot of RhIg (Rh immunoglobulin). If already sensitized, RhIg will have no effect.

If a mother is Rh sensitized and has an Rh+ fetus, an early delivery may be necessary or possibly a blood transfusion is needed. If the anemia is mild enough, the baby can be delivered normally with a possible post-delivery transfusion necessary. Read more about it from The American Congress of Obstetricians and Gynecologists.

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