Biology 101 - Circulatory System Part 2

Fetal hemoglobin has a greater affinity for oxygen than adult hemoglobin.

Specifically, fetal hemoglobin must be more prone to binding oxygen than maternal hemoglobin. This phenomenon allows a developing fetus to accept oxygen from its mother’s partially deoxygenated blood.

Also known as the white blood cell, it is an immune cell that combats infection in the body. Unlike red blood cells, leukocytes do contain nuclei, and are also larger and less numerous.

platelets

In addition to physically blocking lacerations, they activate proteins in the blood called clotting factors.

Platelets are not full cells, but tiny cell fragments derived from larger megakaryocytes. As such, they do not contain nuclei.

fibrin

Fibrin is derived from the soluble precursor fibrinogen.

Another protein, thrombin, cleaves fibrin into its active form. Thrombin also forms from a precursor, called prothrombin.

It is the process by which a liquid becomes a gel. When referring to blood, this process is also called clotting.

Coagulation functions to prevent immediate blood loss from a damaged vessel. It also facilitates eventual repair of the tissue.

First, platelets plug the area of the wound and activate a coagulation cascade. This pathway ends in the activation of fibrin from fibrinogen. Finally, fibrin forms an insoluble crosslinked mesh that seals the laceration.

Hemoglobin has an iron-containing heme group for each of its four protein subunits, allowing it to carry four oxygen molecules total.

Each red blood cell, then, contains around 250 million molecules of hemoglobin, resulting in a carrying capacity of around one billion O2 molecules per erythrocyte.

Most carbon dioxide (70-80%) is carried in the form of bicarbonate ions, HCO3-. These ions comprise an integral part of the blood buffer system.

The remaining CO2 is either bound to hemoglobin or dissolved in its original form in the plasma.

It is a substance that causes an immune response. Specifically, antigens are markers that can be recognized by antibodies.

The surface proteins that determine blood type (A and B) are examples of antigens.

Blood type is classified based on the surface antigens present on a person's erythrocytes.

Human blood types include A, B, AB, and O. While A and B denote possible antigens, an O blood type implies that neither is present.

Also known as the Rh factor, this refers to a surface antigen on human blood cells that was first discovered in Rhesus monkeys.

Rh positive (Rh+) blood displays the Rh antigen, while Rh negative (Rh-) blood lacks it. Rh- blood can be given to individuals of either blood type, while Rh+ blood is only given to other Rh+ people.

An immune protein that recognizes a specific, potentially harmful antigen or class of antigens. Antibodies are produced by B lymphocytes.

• AB+ individuals are universal acceptors.

• Those with O- blood are universal donors.

Since AB+ individuals have all the major surface antigens, they produce no antibodies and can accept blood of any type. In contrast, O- blood has no surface antigens and thus will not induce an immune response upon transfusion.

The donor blood must not contain surface antigens that are foreign to the recipient. In other words, the donated blood must not induce the production of antibodies.

The recipient must have all of the surface antigens that are present on the donated blood cells. This is necessary to prevent the production of antibodies.

For example, if the recipient is AB-, she can accept blood with either A or B antigens (or both). However, she cannot accept blood that contains the Rh factor.

In a process called hemagglutination, the recipient's antibodies cause the transfused blood to bind and clump together.

Antibodies against the A and Rh antigens.

An individual's blood type denotes which antigens are present on his red blood cells. Antibodies will be produced only for foreign antigens - in other words, those antigens that are not part of the blood type. B- blood contains only B antigens, so all others will be considered foreign.

• A+

• A-

• O+

• O-

Simply put, an A+ individual can receive blood as long as it does not contain antigens other than A and Rh. The only antigen that violates this rule is B, so the person could not receive B+, B-, AB+, or AB- blood.

The mother may develop antibodies against the Rh factor, which could affect future pregnancies.

Since fetal and maternal blood are separated, development of antibodies usually does not occur until birth. The first baby, then, will be unaffected. However, if the mother becomes pregnant with a second Rh+ fetus, her antibodies may attack its cells. This is known as hemolytic disease of the newborn, or erythroblastosis fetalis.