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mbilical cord blood was once regarded as medical

U waste. In 1983, researchers at Duke University discovered that cord blood is a rich, abundant source of stem cells that give rise to specialized blood cells. Because it can replenish a person's blood supply, umbilical cord blood is today used to treat certain tumors, immunodeficiency syndromes, anemias, leukemias, and other blood disorders. The technique has saved more than 500 lives worldwide, many of them children suffering from rare inherited disorders.

Using stem cells from umbilical cord blood to treat these conditions offers many advantages over an older approach, bone marrow transplantation. Unlike the stem cells that are exceedingly rare in bone marrow, those in umbilical cord blood are abundant. Collecting blood from the umbilical cord does not hurt the donor. Compared to bone marrow stem cells, those in the umbilical cord blood are less likely to attack a recipient's tissues, a deadly condition called graft-versus-host disease. Cord blood transplants have a higher success rate and lower infection rate than bone marrow transplants. Because cells fresh from a fetus are less able to stimulate an immune response, they need not be as closely matched to the recipient as are bone marrow cells.

The first umbilical cord blood transplant was performed in 1988, on a five-year-old named Matthew Farrow with Fanconi anemia, an inherited severe lack of red blood cells. The stem cells came from his sister's umbilical cord. In 1990, the technique cured a child of leukemia. In 1992, the National Heart, Lung and Blood Institute established a placental blood bank, which treated two dozen children—more than half responded extremely well. Soon the agency was sponsoring a network of similar facilities, and commercial umbilical cord blood storage services are now available. These banks screen donated cord blood for infectious agents and genetic disease, standardize collection procedures, and measure the percentage of stem cells per sample. A unit of donor cord blood is usually sufficient to treat a child or small adult.

Today, a few couples have used assisted reproductive technologies (described in chapter 22, p. 914) to conceive and then select embryos whose umbilical cord blood can provide stem cells to save the lives of siblings with diseases such as Fanconi anemia. More commonly, many new parents are routinely asked to donate cord blood—either to treat their own child should he or she develop a blood or immune disorder some day or to help another person.

Blood is often considered a type of connective tissue whose cells are suspended in a liquid intercellular material. Blood is vital in transporting substances between body cells and the external environment, thereby helping to maintain a stable internal environment.

Blood travels through tubular structures called blood vessels. It leaves the heart through arteries and flows on through the smaller arterioles. Diffusional exchange of nutrients and waste materials between blood and tissues occurs across the thin-walled capillaries. Finally blood returns to the heart through the very small venules and progressively larger veins. Blood vessels will be discussed in Chapter 15 (p. 602).

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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