Understanding the Human Circulatory System and Blood Groups
The Circulatory System
The circulatory system is responsible for transporting substances throughout the body. It consists of a pump (the heart), a liquid (blood), and a series of vessels (blood vessels) through which blood is pumped. The blood reaches all parts of the body, collecting tissue debris and carbon dioxide, and delivering oxygen and nutrients needed by cells.
Composition of Blood
Blood consists of a liquid called plasma and different types of blood cells. Blood plasma is a thick, yellowish liquid consisting primarily of water and other substances. Blood cells are of three types:
- Red blood cells (erythrocytes): Cells that have lost their nucleus and are essentially bags of hemoglobin.
- White blood cells (leukocytes): Important for immune defense.
- Platelets (thrombocytes): Essential for blood clotting.
Other Functions of Blood
Besides transporting substances, blood performs other functions:
- Distributes body heat.
- White blood cells defend the body against infections.
- Platelets in the blood coagulate at wounds and help stop bleeding.
Human Blood Groups
In humans, there are four main blood groups, designated by the letters A, B, O, and AB.
- Group A: Red blood cells have agglutinogen A on their plasma membrane. The plasma contains anti-B agglutinins (antibodies against agglutinogen B).
- Group B: Red blood cells have agglutinogen B. The plasma contains anti-A agglutinins (antibodies against agglutinogen A).
- Group O: Red blood cells lack agglutinogens on their surface. The plasma contains both anti-A and anti-B agglutinins (antibodies against both types of agglutinogens).
- Group AB: Red blood cells have both A and B agglutinogens on their plasma membranes, but the plasma contains no agglutinins.
Blood groups are determined by the presence or absence of agglutinogens and agglutinins. These substances are protein molecules. Individuals with Type A blood (membrane protein A) produce antibodies against the protein B membrane. Group B individuals produce agglutinins against protein A. Those with AB blood (agglutinogens A and B in their red blood cells) do not produce antibodies against proteins A and B. Finally, individuals with Group O blood make antibodies against both proteins A and B.