By Henrylito D. Tacio

Blood is essential for good health because the body depends on a steady supply of fuel and oxygen to reach its billions of cells. Even the heart couldn’t survive without blood flowing through the vessels that bring nourishment to its muscular walls. Blood also carries carbon dioxide and other waste materials to the lungs, kidneys, and digestive system; from there they are removed from the body.

“Without blood, we couldn’t keep warm or cool off, we couldn’t fight infections, and we couldn’t get rid of our own waste products,” points out Dr. Steven Dowshen, of the Division of Endocrinology at the Alfred I. duPont Hospital for Children in Wilmington, Delaware.

According to the Oxford English Dictionary, the word “blood” dates to the oldest English, circa 1000 AD. The word is derived from Middle English, which is derived from the Old English word blôd, which is akin to the Old High German word bluot, meaning blood. The modern German word is (das) Blut.

Due to its importance to life, blood is associated with a large number of beliefs. For instance, in the Jewish and Christian religions, blood is given particular emphasis because the Bible states: “the life of a creature is in the blood” (Leviticus 17:11).

Blood accounts for eight percent of the human body weight, with an average density of approximately 1,060 kilograms per cubic meter, very close to pure water’s density of 1,000 kilograms per cubic meter.

There are four main types of blood: A, B, AB, and O. For each type, the blood is either Rh-positive or Rh-negative. For example, a person with O-negative blood has red blood cells that lack both A and B antigens and the Rh factor. A person with AB-positive blood has red blood cells that have A and B antigens and the Rh factor. Some blood types are far more common than others.

In an emergency, anyone can receive type O red blood cells; thus people with type O are known as universal donors. People with type AB blood can receive blood cells from any blood type and are thus known as universal recipients. Recipients whose blood is Rh-negative must receive blood from Rh-negative donors, but recipients whose blood is Rh-positive may receive Rh-positive or Rh-negative blood.

Actually, blood is a complex mixture of plasma (the liquid component), white blood cells, red blood cells, and platelets. “The body contains about five to six quarts of blood,” notes The Merck Manual of Medical Information. “Once blood is pumped out of the heart, it takes 20 to 30 seconds to make a complete trip through the circulation and return to the heart.”

Plasma – which constitute more than half of the blood’s volume – is 90% water and contains nutrients, proteins, hormones, and waste products. Some of the protein actively defends the body against viruses, bacteria, fungi, and cancer cells, and clotting factors, which control bleeding.

“Plasma also acts as a reservoir that can either replenish insufficient water or absorb excess water from tissues,” the Merck manual informs. “Plasma likewise prevents blood vessels from collapsing and clogging and helps maintain blood pressure and circulation throughout the body simply by filling blood vessels and flowing through them continuously.”

The blood that flows through this network of veins and arteries is called whole blood. Whole blood contains three types of blood cells: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Red blood cells – which make up about 40% of the blood’s volume – contain hemoglobin, a protein that gives blood its red color and enables it to carry oxygen from the lungs and deliver it to all body tissues.

“When the number of red blood cells is too low (anemia), blood carries less oxygen, and fatigue and weakness develop,” the Merck manual states. “When the number of red blood cells is too high (polycythemia), blood can become too thick, which may cause the blood to clot more easily and increase the risk of heart attacks and stroke.”

White blood cells are fewer in number than red blood cells, with a ratio of about one white blood cells to every 660 red blood cells. They are responsible primarily for defending the body against infection.

“When the number of white blood cells is too low (leucopenia), infections are more likely to occur,” the Merck manual says. “A higher than normal number of white blood cells (leukocytosis) may not directly cause symptoms, but the high number of cells can be an indication of a disease such as an infection or leukemia.”

Platelets – smaller than red or white blood cells – are few in number than red cells, with a ratio of about one platelet to every 20 red blood cells. They help in the clotting process by gathering at a bleeding site and clumping together to form a plug that helps seal the blood vessel.

“When the number of platelets is too low (thrombocytopenia), bruising and abnormal bleeding become more likely,” the Merck manual explains. “When the number of platelets is too high (thrombocythemia), blood may clot excessively, producing a stroke or heart attack.”

In an article which appeared in Health and Lifestyle some years back, author Ellen Joy U. Castel wrote of three main organs that affect blood processes in the body: kidneys, liver, and spleen. “Each of the three has roles in making and processing the blood,” she pointed out.

About 200 quarts of blood are processed daily in the kidneys. “The kidneys regulate the blood composition by keeping the concentrations of ions and elements constant together with water volume and acid-base concentrations,” Castel wrote. “Apart from that, they are responsible for filtering and removing wastes and toxins from the body sent to the blood; and are responsible for producing erythropoietin, a hormone which stimulates red blood cell production in the bone marrow.”

Aside from regulating the blood sugar and the level of different types of fats in the blood, the liver also disposes worn-out red blood cells and removes excess protein, lipids and amino acids in the blood. “On top of it all, the liver makes plasma proteins which are needed in blood clotting,” wrote Castel.

The spleen has two primary functions: one, it filters the blood and removes abnormal cells (such as old and defective red blood cells); and two, it makes disease-fighting components of the immune system (including antibodies and lymphocytes).

Dr. Francisco F. Lopez, hematology and medical oncology specialist at the Makati Medical Center and Asian Hospital and Medical Center, says blood health can be determined through the analysis of the complete blood count (CBC).

The CBC is the calculation of the cellular component of the blood. The Merck manual listed seven tests: hemoglobin (amount of the oxygen-carrying protein within red blood cells), hematocrit (proportion of total blood volume made up of red blood cells), mean corpuscular volume (average volume of individual red blood cells), white blood cell count (number of white blood cells in a specified volume of blood), differential white blood cell count (percentages of the different types of white blood cells), platelet count (number of platelets in a specific volume of blood), and mean platelet volume (average volume of platelets).

“You have to get your CBC,” says Dr. Lopez. “If your blood composition is not balanced, then you are not healthy. There’s a problem with your blood.”

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