Human Biology Chapter 6 Section 5: Human Blood Types

ABO Blood Groups

ABO blood typing is based on the presence or absence of two possible antigens, called type A antigen and type B antigen. Whether these antigens are present or not depends on the inheritance of the individual. -Type A blood has the A antigen (blue spheres) and type B blood has the B antigen (violet triangles) -Type AB blood has both A and B antigens -Type O blood has neither antigen on its red blood cells.

Blood Compatibility

Blood compatibility is very important when transfusions are done. The antibodies in the plasma must not combine with the antigens on the surface of the red blood cells or else agglutination occurs. With agglutination, anti-A antibodies have combined with type A antigens, and anti-B antibodies have combined with type B antigens. Therefore, agglutination is expected if the donor has type A blood and the recipient has type B blood. The same situation occurs if the donor has type B blood and the recipient has type A blood.

Explain what determines blood type, and list the four types of blood.

Blood types A, B, AB, and O are based on the presence or absence of type A antigen and type B antigen.

Blood Type and Crossmatch

Blood typing refers to genetically determined antigens on the surface of the red blood cell used to determine blood groups (A, B, O). Crossmatching is a procedure used to determine compatibility of a donor's blood with that of the recipient. Both tests are performed prior to blood transfusion. Type O blood donation without crossmatching is performed only in an emergency, when blood loss is severe and the patient's survival is at stake.

Agglutination

Clumping of red blood cells due to a reaction between antigens on red blood cell plasma membranes and antibodies in the plasma. -does not occur when blood from different people is mixed

The ABO blood type system

In the ABO system, blood type depends on the presence or absence of antigens A and B on the surface of red blood cells. In these drawings, A and B antigens are represented by different shapes on the red blood cells. The possible anti-A and anti-B antibodies in the plasma are shown for each blood type. An anti-B antibody cannot bind to an A antigen, and vice versa.

What is the most common ABO blood type? What is the least common?

In the United States and other countries with a large immigrant population, the most common ABO type is type O. However, type A blood is most common in several European countries, including Portugal, Armenia, Switzerland, and Norway. Worldwide, type B blood is common in central Asia, India, and the Far East. Worldwide, the least common ABO type is type AB.

Blood transfusion

Introduction of whole blood or a blood component directly into the bloodstream. -For transfusions to be done safely, blood must be typed, so that agglutination (clumping of red blood cells) does not occur when blood from different people is mixed. -Only certain types of blood transfusions are safe, because the plasma membranes of red blood cells carry glycoproteins that can be antigens to other individuals.

Explain what causes hemolytic disease of the newborn.

Once an woman has been exposed to the Rh antigen (usually during delivery of an Rh+ baby), she makes anti-Rh antibodies. During subsequent pregnancies, these antibodies cross the placenta and destroy the Rh+ fetal red blood cells.

How to prevent the Rh problem

The Rh problem is prevented by giving Rh-negative women an Rh immunoglobulin injection no later than 72 hours after giving birth to an Rh-positive child. This injection contains anti-Rh antibodies that attack any of the baby's red blood cells in the mother's blood before these cells can stimulate her immune system to produce her own antibodies. Called RhoGAM, this treatment does not harm the newborn's red blood cells; however, the treatment is not beneficial if the woman has already begun to produce antibodies. Therefore, the timing of the injection is most important.

Rh Blood Groups

The designation of blood type usually also includes whether the person has or does not have an antigen, called the Rh factor, on the red blood cell. Rh-negative individuals normally do not have antibodies to the Rh factor, but they make them when exposed to the Rh factor. If a mother is Rh-negative and the father is Rh-positive, a child can be Rh-positive. During childbirth, Rh-positive antigens can leak across the placenta into the mother's bloodstream. The presence of these Rh-positive antigens causes the mother to produce anti-Rh antibodies.

blood type

The term blood type refers to variations in the surface proteins found on the surface of red blood cells (RBCs). Blood typing usually involves determining the ABO blood group and whether the individual is Rh-negative or Rh-positive.

Explain who a donor with type A blood is able to donate blood to.

Type A can give to type A or AB.

Type AB blood

Type AB blood is sometimes called universal recipient blood, because the plasma lacks A and B antibodies. Agglutination should not occur when a person with type AB blood receives a transfusion from a donor with any other type of blood.

Type O blood

Type O blood is sometimes called the universal donor, because the red blood cells of type O blood lack A and B antigens. When type O blood is donated to a recipient with any other blood type, agglutination should not occur.

Types A and B blood

Types A and B blood have antibodies (yellow, Y-shaped molecules) that correspond to the antigens they do not have on their own cells. -An individual with type A blood has anti-B antibodies in the plasma, and a person with type B blood has anti-A antibodies in the plasma. -AB blood lacks both antibodies -Anti-A and/or anti-B antibodies are not present at birth, but they appear over the course of several months. -The anti-B antibodies have a triangular binding site on the top of each Y-shaped molecule. This binding site fits snugly with the purple, triangular B antigen. -The anti-A antibodies have a spherical binding site shaped to form a perfect fit with the A antigen. -The presence of these antibodies can cause agglutination.

Is ABO blood typing accurate?

Usually, the answer is yes. However, there are some interesting genetic disorders that may complicate traditional ABO blood typing. For example, individuals with Bombay syndrome lack the enzyme to correctly attach A and B antigens to the surface of the red blood cells. These individuals may carry the genes to produce the A and B antigens on the surface of the red blood cells, but because these are not attached, they may appear to have type O blood.

Rh factor disease (hemolytic disease of the newborn)

a. Due to a pregnancy in which the child is Rh-positive, an Rh-negative mother can begin to produce antibodies against Rh-positive red blood cells. b. In pregnancy, these antibodies can cross the placenta and cause hemolysis of the Rh-positive child's red blood cells. -In subsequent pregnancy with another Rh-positive baby, the anti-Rh antibodies can cross the placenta and destroy the unborn child's red blood cells. This is called hemolytic disease of the newborn, because hemolysis starts in the womb and continues after the baby is born. Due to red blood cell destruction, the baby will be severely anemic. Excess hemoglobin breakdown products in the blood can lead to brain damage and intellectual disability, or even death.