O

What is the main concern when blood is transfused from one individual to another?

Why is a type AB person called a universal recipient? Why is a type O person called a universal donor?

When is type O blood not really type O blood? Blood typing involves adding known antibodies to a blood sample to see if the blood will clump, demonstrating the presence of corresponding antigens on the red blood cell membranes. A person with a rare genetic condition called the Bombay phenotype lacks an enzyme that inserts a particular sugar onto red blood cell surfaces. Without that sugar, the A and B antigens cannot bind. The result is blood that tests as O (because it lacks A and B antigens) but can genetically be of any ABO type—A, B, AB, or O. Although the Bombay phe-notype does not affect health, it can sometimes explain a child's ABO type that cannot be derived from those of the parents.

and will begin producing anti-Rh antibodies. Generally, no serious consequences result from this initial transfusion, but if the Rh-negative person—who is now sensitized to Rh-positive blood—receives another transfusion of Rh-positive blood some months later, the donated red blood cells are likely to agglutinate.

A related condition may occur when an Rh-negative woman is pregnant with an Rh-positive fetus for the first time. Such a pregnancy may be uneventful; however, at the time of this infant's birth (or if a miscarriage occurs), the placental membranes that separated the maternal blood from the fetal blood during the pregnancy tear, and some of the infant's Rh-positive blood cells may enter the maternal circulation. These Rh-positive cells may then stimulate the maternal tissues to begin producing anti-Rh antibodies (fig. 14.23).

If a woman who has already developed anti-Rh antibodies becomes pregnant with a second Rh-positive fetus, these anti-Rh antibodies, called hemolysins, cross the pla-cental membrane and destroy the fetal red cells. The fetus then develops a condition called erythroblastosis fetalis (hemolytic disease of the newborn). Clinical Application 14.5 discusses human blood transfusions and substitutes.

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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