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All About Blood

Reviewed By: Dr. Kurt Kloss, MD
Last Reviewed Date: Jan 30, 2018
Last Modified Date: Jan 30, 2018
Published Date: Jan 30, 2018

Blood is one of the most important elements of the human body. It is vital for life, and without it, the body cannot function properly. In the average adult, blood accounts for as much as 7 percent of the body's weight; there's up to 1.5 gallons of blood in the body of a person weighing between 150 and 180 pounds. When a person suffers from extreme blood loss, a transfusion of blood is often necessary to help keep them alive. Because anyone could find themselves in need of blood, it's beneficial for people to learn the basics regarding this life-sustaining fluid.

Your Body and Blood

Blood is a combination of red blood cells, white blood cells, platelets, and plasma, all of which serve an important function. Each of these components is manufactured by the body and cannot be made artificially. Red and white blood cells and platelets, for example, are produced in the marrow of bones. Blood is also considered a crucial part of the circulatory system. With each beat of the heart, blood is pumped through a system of blood vessels, which allows it to circulate through every part of the body.

Red Blood Cells

There are roughly 37 trillion cells in the human body. The majority of these are red blood cells, which are estimated to number between 20 to 30 trillion at any given time. Also known as erythrocytes, these cells have a round yet somewhat flattened appearance, with a slight indentation in the center. The red coloring comes from hemoglobin, which is a protein that contains iron. With the help of hemoglobin, red blood cells carry oxygen through the body and help to carry away waste such as carbon dioxide. From the time that red blood cells are produced, they have a lifespan of approximately 120 days.

White Blood Cells

Also known as leukocytes, white blood cells help combat infections and disease. These cells are larger than red blood cells and do not have the same coloring. Additionally, while erythrocytes are the most plentiful cells in the body, white blood cells are few in healthy bodies. This changes, however, if a person should become ill, as this causes the body to produce more leukocytes to protect itself. White blood cells are found in both the blood and in lymph tissue. There are three types of white blood cells: granulocytes, monocytes, and lymphocytes. Granulocytes are a type of white blood cell that has tiny granules inside of them. These granules contain enzymes that help combat bacteria, parasites, and viruses. They make up most of one's white blood cells. There are several types of granulocytes, including basophils, eosinophils, and neutrophils. Lymphocytes can be broken into two categories: B cells and T cells. When a body is under attack from viruses, bacteria, or toxins, the antibodies needed to combat them are produced by B cells. If there are cancer cells or body cells are taken over by viruses, the T cells attack those compromised cells. Monocytes are the white blood cells with the longest lifespan and are the largest of the white blood cells. When they are released, they can leave the bloodstream and enter tissue, where they mature into macrophages. Monocytes surround and destroy microorganisms, remove dead cells, and boost immune response.

Platelets

Platelets are small, plate-shaped cells that prevent excess blood loss when a blood vessel is broken by a cut or some other injury. When injuries like this occur, a signal is sent out that causes platelets to respond and travel to the damaged area. At the damaged site, the platelets bind together to create a type of plug. A chemical is released to make protein threads that work together with platelets to form clots that stop the bleeding.

Plasma

Plasma is the liquid portion of blood that makes up 55 percent of its volume. This clear yellow liquid consists of hormones, cells, enzymes, and nutrients, but it is approximately 92 percent water. The proteins that aid in blood clotting are also in plasma. In addition to carrying blood cells and platelets through the body, plasma also maintains blood pressure, helps balance the body's pH levels, aids in fighting certain diseases, and carries away cell waste.

What's Your Type?

Although blood circulates through every human body, it isn't all the same. Blood is divided into types. There are eight blood types that are determined by the presence or lack of certain antigens. Blood types are described by three letters: A, B, and O. Type A blood contains the A antigen, while type B blood contains the B antigen. When a blood type has both A and B antigens it is type AB; however, if it has neither A or B antigens, it is blood type O. These are further differentiated by the Rh factor. Blood types with the Rh factor are positive, and if this protein isn't present, the blood type is negative. Therefore, the possible blood types are A positive, A negative, B positive, B negative, O positive, O negative, AB positive, and AB negative.

A person's blood type is determined by their genes. It's crucial to know someone's blood type if they need a blood transfusion, as it determines who a person can receive blood from. If a person receives the wrong blood type, they can have an ABO incompatibility reaction that's potentially fatal. People should know what their blood type is, but if they don't, they can find out by asking their parents or by purchasing and using tests from health testing centers. Hospitals will test one's blood type before doing a blood transfusion, but in an emergency, they can use O negative blood: It has none of the three antigens and is safe for everyone to receive.

The Truth About Transfusions

Every year, millions of people require additional blood in the United States through a blood transfusion, which is blood that comes from another person who has a compatible blood type. The blood used for transfusions is given on a volunteer basis, and it must meet strict safety standards before it may be used. People can only donate blood if they are free of bacterial contamination and certain diseases that can be spread to others, such as HIV and hepatitis. At blood banks, certain blood safety basics are adhered to. Donor blood is screened starting with a questionnaire regarding their health, followed by testing of the donated blood for transfusion-transmitted viruses and other infectious pathogens. Staff are required to use only new needles and to keep only blood that is free of disease while discarding any that is not.

Why Transfusions?

People who lose a lot of blood due to a serious injury or while having major surgery often need a blood transfusion. An illness that causes anemia can also result in the need for a transfusion that will help to raise the individual's blood count. Transfusions can be done in a doctor's office or at a hospital using autologous blood, which is the patient's own blood, or donor blood. Autologous blood is a potential option when a surgery is elective and planned. In general, transfusions take as little as an hour or as long as four hours, though in an emergency, blood transfusions may be done more quickly.

  • Surgeries and Procedures: Blood Transfusions: Click this link to visit a page that discusses information about blood transfusions, why they are performed, and the process.
  • Interesting Facts About Blood: People interested in learning about blood can click this link to the ThoughtCo website for 12 interesting facts.
  • How Blood Works: Learn about cells, plasma, and how blood works by clicking on this link to the HowStuffWorks website.
  • Blood: We Can't Live Without It: Kids and their parents can visit this site to read information about blood, including blood types, transfusions, and a section on interesting blood-related facts.
  • Blood Components: Blood is made up of several components that are listed and described on this page.
  • Facts About Blood and Blood Cells: Visit this page by the Memorial Sloan Kettering Cancer Center to read about red and white cells, platelets, and plasma.
  • Histology Guide: Functions and Constituents: This University of Leeds page reviews the functions of the blood and provides information about blood cells and plasma.
  • The ABOs of Blood Types: People who are curious about blood types may visit this page about blood types and which type is the universal donor.
  • Blood Typing: Students or anyone who is interested in blood typing can click this link to find information including a table to illustrate the different types.
  • ABO Blood Types in Humans: Click this link to view a blood type table and a distribution of blood types in the human population.
  • These Eight Groups of People Are More Prone to Blood Clots: Fox News offers this article that educates readers about the risks of blood clots for people in certain groups, including those who are overweight, smokers, or sedentary.
  • What Is a Blood Transfusion? Individuals who need a blood transfusion can learn more about the procedure and risks by clicking on this link.
  • Blood Transfusions During Pregnancy: Pregnant women with questions regarding blood transfusions can read about some of the reasons why they may need one during their pregnancy and the potential risks.
  • Health A to Z: Blood Transfusion: NHS Choices provides site visitors with information about blood transfusions including why they are done, what happens, risks, and alternatives.
  • Low Platelet Count: What Does it Mean? This American Family Physician page helps readers to better understand what platelets are and what it means to have a low platelet count.
  • Platelets on the Web: People can read and learn about platelet counts, structure, and function as well as a brief description of red and white blood cells here.
  • Red Blood Cells: Click this link to read information from the BBC about red blood cells and adaptations.
  • Components of Blood: The Merck Manual provides patients and their families with an outline of the main components of blood.
  • Heart Information Center: Blood: The Texas Heart Institute explains blood, types of blood cells, and blood types to patients or anyone who visits this page on their website.
  • The Clinical Use of Blood Handbook (PDF): Open this document from the World Health Organization to read about the clinical uses of blood, including in-depth information on transfusions, risks, components, and storing and administering blood products.