your body temperature is increasing, it sends messages to the blood vessels in the skin to
increase in diameter. Increasing the diameter of the blood vessels increases the amount of
blood and heat that moves near the skin surface. The heat is then released from the skin.
Blood Clotting
Blood clottingis a complex process by which blood forms solid clots. As discussed above,
clotting is important to stop bleeding and begin repair of damaged blood vessels. Blood
clotting disorders can lead to an increased risk of bleeding or clotting inside a blood vessel.
Platelets are important for the proper clotting of blood.
Clotting is started almost immediately when an injury damages the inside lining of a blood
vessel. Platelets clump together, forming a plug at the site of injury. Then, proteins in the
plasma cause a series of chemical reactions that form a tough protein calledfibrin. The
fibrin strands form a web across the platelet plug, trapping red blood cells before they can
leave through the wound site. This mass of platelets, fibrin, and red blood cells forms a clot
that hardens into a scab.
Certain nutrients are needed for the clotting system to work properly. Two of these are
calcium and vitamin K. Bacteria that live in your intestines make enough vitamin K so you
do not need to eat extra vitamin K in your food.
Blood Types
Blood typeis determined by the presence or absence of certain molecules, calledantigens,
on the surface of red blood cells (RBCs). There are four blood types; A, B, AB, and O.
Type A blood has type A antigens on the RBCs in the blood.
Type AB blood has A and B antigens on the RBCs.
Type B has B antigens on the RBCs.
Type O does not have any antigens (neither A nor B).
Thebloodtypesmayalsohaveantibodiesforotherbloodtypesintheirplasma. Forexample,
a person with type A blood may have anti-B antibodies (against B antigens), and a person
with type O blood can have anti-A and anti-B antibodies in their blood. The blood type
of a person can be worked out by testing a drop of a person’s blood using anti-A or anti-B
antibodies.
The ABO blood group system is most important if a person needs a blood transfusion. A
blood transfusionis the process of putting blood or blood products from one person into
the circulatory system of another person.
If a person with type O blood received type A blood, the anti-A antibodies in the person’s