(microscopic image of blood components)
To better understand the connotations of gender and power in blood, the basic background behind its medical components should be explored. The ways in which blood is scientifically understood currently and historically helps define the ways in which people view blood.
Blood: fluid that is pumped by the HEART and circulates through the body via arteries, veins, and capillaries, carrying oxygen and nutrients to the body tissues, and carbon dioxide and wastes away from them (see CIRCULATORY SYSTEM). It is also involved in tissue repair, cell METABOLISM, infection resistance, and other life-sustaining activities. Blood is made up of plasma, a colorless fluid containing red blood cells (erythrocytes), which carry on oxygen-carbon dioxide exchange; white blood cells (leukocytes), which defend the body from foreign agents; platelets that function in blood clotting; HORMONES; and essential salts and PROTEINS. There are about 6 quarts (5.6 liters) of blood in an average-sized adult male human. Blood is classified into BLOOD GROUPS. A deficiency of red blood cells is ANEMIA; abnormal proliferation of leukocytes is known as LEUKEMIA. See also BLOOD BANK; BLOOD TRANSFUSION.
The Concise Columbia Encyclopedia is licensed from Columbia University Press. Copyright 1995 by Columbia University Press. All rights reserved.
Historical Blood Beliefs
(Galen and Hippocrates)
More ancient "scientific"
theory held that blood was one of the four "humors"
this theory was developed by Galen (ca.130-ca 200) in ancient Greece and remained
in belief through the middle ages. Galen believed that "blood originated
in the liver, and sloshed back and forth through out the body, passing through
the heart, where it was mixed with air, by pores in the septum"(5). His
theory stated that the body held four different fluids which consisted of Blood(associated
with the heart), Yellow Bile(associated with the brain), Phlegm(associated with
the liver), and Black Bile(associated with the spleen), and were based on the
four elements of fire(yellow bile), air(blood), earth(black bile), and water(phlegm)(1).
Each of the humors was believed to be responsible for different types of personality.
An excess of blood made a person sanguine, yellow bile resulted in a choleric
personality, phlegm produced a phlegmatic outlook, and black bile was associated
with melancholia (2). "The 'humors. gave off vapors which ascended to the
brain; an individual's personal characteristics (physical, mental, moral) were
explained by his or her 'temperament,' or the state of that person's 'humors.'"(3).
These theories spurred the medical treatment known as bloodletting or phlebotomy, and was believed to make
a person healthy by bleeding them, and getting rid of the "bad humors."
On occasion "therapeutic phlebotomy"
is still used today (4). Paracelsus (ca1493-ca1541) attacked the ideas of the
elements with a basic argument of macrocosm, this lead to the modern idea of
medicine and the application of alchemy in the treatment of diseases (8).
Sources and Related Sites
1. Giblin, James Cross. When Plague Strikes: The Black Death, Smallpox, Aids. New York; Harper Collins Publishers, 1995.
(Clotted red blood cells, courtesy of Photo Researchers, Inc. May not be reproduced without permission)(1).
The heart pumps blood through our bodies at a rate of 5 liters
per minute while at rest and 20-30 liters per minute during heavy exercise(9). The average adult has around 5 liters
of blood in their bodies.
"Blood is the fluid of life, transporting oxygen from the lungs to the body tissue and carbon dioxide from body tissue to the lungs. Blood is the fluid of growth, transporting nourishment from digestion and hormones from glands throughout the body. Blood is the fluid of health, transporting disease fighting substances to the tissue and waste to the kidneys"(3).
The General Functions of blood, biologically speaking, concern metabolism and its regulation, transport, osmotic balance and defense. In certain instances transport and metabolic functions are
closely linked with each other. For instance in the carriage of oxygen and carbon dioxide, the movement of metabolites as well as the functions of osmoregulation we can observe how these two roles of blood overlap. Science has taught us that blood is "really a tissue made up of a liquid matrix containing several types of cells. About half the volume of blood is made up of a fluid called plasma, and the other half is blood cells." (8).
The cells of the blood can be separated from the plasma by a machine that is called centrifuge. A separated sample of blood looks like the below diagram. The plasma is at the top, then the white cells, then platelets. At the bottom of the bag are the packed cell volume or hematocrit consisting of red blood cells. People living at a higher altitude have higher hematocrit levels, men average a level of 42% and women 38%.
.Red Blood Cells.
Red Blood cells transport oxygen and carbon dioxide throughout the body. "Each red blood cell is round and bi-concave (meaning both surfaces are hollowed out)"(5). There are millions of red blood cells in a single drop of blood. Red blood cells form from the stem cells. "Stem cells are found in bone marrow, in ribs, the breastbone, pelvis, and vertebrae. Red Blood cell production is controlled by the hormone, erythropoietin, which is released by cells in the kidney in response to insufficient oxygen"(2, pg. 972). In healthy normal functioning the body can produce about two million red blood cells every second. While the red blood cells are still developing in the bone marrow the cells are dividing, it is at this point when hemoglobin is produced. Hemoglobin is a protein that brings oxygen from the lungs to the tissues and delivers myoglobin for storage. Hemoglobin contains the red pigment that colors blood and is iron based enabling it to pick up oxygen and wastes. Myoglobin is also a protein but its function is to store oxygen in certain tissues. "Each subunit of hemoglobin is folded like a myoglobin molecule, suggesting that both hemoglobin and myoglobin are evolutionary decedents of the same oxygen binding ancestral protein." (2, pg. 55). When the red blood cells hemoglobin amount is around "thirty percent, the nucleus, endoplasmic reticulum, golgi apparatus, and mitochondria begin to break down"(2, pg. 972). At this point the new red blood cell enters into circulation. The cells only circulate for about 120 days. After their tour of the body they begin to break down for recycling. "The iron from the hemoglobin molecule is recycled to the bone marrow"(2, pg. 972). There are 5 million red blood cells per milliliter of blood and only 5,000 to 10,000 white blood cells (2, pg. 971).
.White Blood Cells.
White blood cells defend the body against infection, by destroying foreign cells, consuming bacteria, debris, and even dead or damaged cells from our own bodies, and producing antibodies. There are 7,000 to 25,000 white blood cells in a single drop of blood. When the immune system detects a foreign factor in the blood it send the appropriate defender to do the job. White blood cells either produce antibodies to overpower the invader, or surround and devour the bacteria. The disease AIDS attacks these cells weakening the immune system so that the body can no longer protect itself.
Blood has cellular elements suspended in an aqueous medium, called plasma. Plasma is the "liquid portion of the blood, in which blood cells and other particulates are suspended"(2). Plasma is a complex composition of gases, ions, nutrients, molecules, and proteins. Most of the ions are Na+ (sodium) and Cl- (chlorine), which explains the salty taste that blood has, but there are many other ions present. Plasma carries all of the components of blood throughout the body.
Platelets are tiny fragments
of large cells in bone marrow, without any nucleus. The platelets function in
sealing leaks in the blood vessels, otherwise known as clotting. (Look to the
top of this section to view clotted cells). There are about 250,000 to 450,000
platelets per milliliter of blood (2). Without Platelets humans would bleed
Sources and Related Sites
1. Photo Researchers Inc., 60E. 56th St., New York, NY 10022
2. Purves, Orians, and Heller. Life the Science of Biology. et. all, 1995, G24.
8. Arms, Karen and Pamela S. Camp. Biology. 3d edition. Philadelphia: Saunders College Publishing, 1987.
.Blood Types and Donation.
There are four types of human blood A, B, AB, and O. Austrian
scientist Karl Landsteiner observed two distinct chemical molecules which attach themselves to the red blood cells
in the early 20th century. These molecules were labeled "A" and "B." The presence of only A
molecules results in type A blood. The presence of only B molecules results in type B blood. The presence of both
molecules results in type AB blood. Finally when no molecules are present the blood is deemed type O blood. If
blood of different types are mixed they may being to clump together in the veins, sometimes causing fatal conditions(3).
Another factor which divides blood into negatives and positives is the RH factor. A blood protein called Rhesus (Rh) was discovered by scientists studying the Rhesus monkeys in an attempt to learn more about the human anatomy due to the similarities between the species. If blood contains Rh then it is positive, if it does not it is negative. "If you are Rh+, your blood cells have the Rh marker and your antibodies ignore it. If, however you are 'Rh negative' your immune system will treat the Rh marker as foreign"(2). Thus causing problems in mothers who have babies with Rh+ blood when they are Rh-, because the mothers immune system attacks the babies blood cells.
Blood transfusions are necessary when a large amount of blood is lost by the patient. When blood transfusions are given a perfect match is preferred, but not always possible. Type A blood can receive either A or O type blood. Type B Blood can receive either B or O blood. Type AB can receive either A, B, AB, or O type blood. Type O Blood can give to anyone but only receive type O. Type O blood is a universal donor, while type AB is a universal receiver.
Below is a table that shows the percentage of the population that has each blood type.
Donated blood is transferred on ice to a component lab where it is separated into red cells, plasma, and platelets. Then it undergoes a series of tests to make sure it is safe to give to the patient in need of a transfusion. The tests consist of: ABO typing, Rh factor, Hepatitis B surface antigen, Antibody to hepatitis B core, Antibody to hepatitis C virus, Alanine Aminotransferase, Antibody to HIV-1, HIV-1 Antigen, Antibody to HTLV-1, Syphilis, and cholesterol. Once the blood is determined as safe for transfusion is is stored appropriatly. "Red cells are refrigerated and have a shelf life of 42 days; plasma is frozen and can be stored for one year; platelets must be rotated at room temperature and have a shelf life of five days"(1). Donating blood is an important community action. Healthy individuals rejuvenate their blood every 52 days after a donation, making it safe to donate blood frequently. Blood donation is considered the gift of life, because blood is essential to life, it is our life-force.
Sources and Related Sites