from “Blood: There Is No Substitute”
By Mary Beth Cox
Read the text, and then answer the questions.
The mythical witch Medea had a great recipe for artificial blood. It called for thousands of ingredients like screech owl wings, water snake skins, crow eggs, stag livers, and werewolf innards. Medea’s specially blended blood substitute was reportedly quite effective. She drained an elderly patient’s tired, old blood and replaced it with a fresh batch of her brew. The gentleman’s health and youthful vigor were magically restored. [...]
We all know there’s no such thing as werewolf innards. But several real substances have been tried as substitutes for human blood. Salt water, animal bloods, ale, wine, and milk have all been pumped into human veins in hopes of finding a stand-in for blood. None of these substances was satisfactory. To date, the only acceptable replacement for human blood is more human blood.
THE NEED FOR A BLOOD STAND-IN
Human blood is given to patients who need it via blood transfusions. A blood transfusion is a medical procedure that transfers a unit of blood from one person (a donor) to another (a recipient). Blood transfusions are usually well tolerated and safe. They’ve been used to save many lives and to improve the quality of many, many more. As a replacement for human blood, donated blood has been an unmatched success. Yet even blood is limited as a substitute for blood. Any two people cannot necessarily share blood. Special care must be taken to match the blood types of a donor and a recipient. Donated blood must also be screened to guarantee it’s free of transmittable diseases [...]. Packets of human blood have a limited shelf life. Even with refrigeration, blood lasts only about a month. Donors are continually needed to replenish stores of blood. Sometimes there are too few donors. This is particularly true in remote areas, during natural disasters, and on battlefields. In such situations, the demand for donated blood can exceed the supply.
These limitations are the reason why some researchers want to develop an artificial substitute for blood. It’s a bit audacious to try to make an artificial blood that’s better at replacing blood than blood. Given the track record of ale, wine, and milk, it isn’t an easy thing to accomplish, either. Artificial blood must be able to do what blood can, but milk can’t. Artificial blood must have the ability to push oxygen around.
Blood has many functions, but its single most critical job is to move oxygen around the body. Blood picks up inhaled oxygen in the lungs and takes it through the circulatory system. Blood drops off oxygen at the body’s various organs and tissues. The importance of blood’s oxygen delivery service cannot be overstated. If organs and tissues don’t get enough oxygen, they cannot work properly. If organs and tissues are deprived of oxygen for too long, they cease to function and die.
Blood is able to move oxygen because of a special ingredient called hemoglobin.
WILL HEMOGLOBIN DO THE JOB?
Hemoglobin is a protein. It is the component of blood that catches and releases oxygen. Hemoglobin grabs oxygen where there’s a lot of it, like in the lungs. Hemoglobin lets go of oxygen where there isn’t much of it, like in hard-working organs and tissues. Milk, like blood, has lots of protein. But milk cannot substitute for blood, because milk doesn’t have hemoglobin.
So why not give patients who need blood a whopping injection of hemoglobin? The reason is that hemoglobin does not float loose in the bloodstream. Hemoglobin is kept inside red blood cells. When red blood cells occasionally burst, the hemoglobin they release is broken up by the liver. This is part of the body’s natural process for disposing of old red blood cells. If hemoglobin is directly injected as a blood substitute, it overwhelms the disposal process. The condition can be fatal.
Even so, some researchers think injected hemoglobin is the key to an artificial blood substitute. The idea is to alter the hemoglobin so that the liver doesn’t break it up. The hemoglobin used in these experiments comes from cow’s blood or from donated human blood that’s past its expiration date. The hemoglobin is altered in one of two ways: A few hemoglobin proteins are joined together to make a multi-hemoglobin polymer, or small guard units are attached to hemoglobin. This is like building the protein a suit of armor.
Artificial hemoglobin was tested in human patients. Unfortunately, there were problems. The altered protein was associated with an increased risk of heart attack and death. It was argued that artificial hemoglobin could still be used to rescue critically injured patients who might otherwise die without immediate blood replacement. [...] The U.S. Food and Drug Administration (FDA) has decided that, at least for the time being, no artificial hemoglobin will be given to human patients.
Future improvements to artificial hemoglobin may reduce the risk. Artificial hemoglobin may eventually be a useful blood substitute. As with any new drug or medical procedure, a balance must be struck between effective treatment and potentially harmful side effects.
The benefits of an artificial blood substitute based on hemoglobin would be many. Blood type matching and disease screening would be unnecessary. Blood substitute could be mass-produced and stored indefinitely. There would be plenty of artificial blood on hand for any, and every, emergency. For the time being, the only help for patients who need blood comes from some very important individuals. These individuals are certainly not witches or werewolves. They are not (yet) the researchers working to come up with an artificial blood substitute. They are the generous donors who contribute blood to their local blood banks. For them, there also is no substitute.
Cox, Mary Beth. “Blood: There Is No Substitute.” Odyssey, vol. 19, no. 3, Mar. 2010, p. 18.
Question
Drag and drop the statements that describe how each paragraph contributes to the text as a whole.
Put responses in the correct input to answer the question. Select a response, navigate to the desired input and insert the response. Responses can be selected and inserted using the space bar, enter key, left mouse button or touchpad. Responses can also be moved by dragging with a mouse.
Paragraph 3
Paragraph 5
Paragraph 10
Paragraph 11
suggests that the problems posed by artificial blood outweigh the benefits of its use in emergency situations
highlights the essential functions of blood in the human body
describes the challenges of providing human blood to patients in need
explains how improvements to artificial blood are necessary in order for it to be an effective human blood substitute
Paragraph 3: describes the challenges of providing human blood to patients in need
Paragraph 5: highlights the essential functions of blood in the human body
Paragraph 10: suggests that the problems posed by artificial blood outweigh the benefits of its use in emergency situations
Paragraph 11: explains how improvements to artificial blood are necessary in order for it to be an effective human blood substitute