Blood Clotting Controls Bleeding 294
• When blood vessels are damaged, three hemostatic mecha-
nisms take place: vascular spasm, platelet plug formation
(shown here), and blood clotting.
Platelet plug formation • Figure 10.7b
;Collagen fibers,
’and damaged
endothelium
Red blood cell
Platelet
Wf.
• Blood clotting is a complex process in which insoluble fibrin
threads form to seal a tear or hole. Blood clotting involves a
number of chemical reactions and ends with the formation
of fibrin strands. Clotting involves various clotting factors,
ionized calcium, plasma proteins, and enzymes.
• Clots get dissolved during a process called fibrinolysis. A
connective tissue covering is then created to permanently
seal the wound. •
• A clot, called a thrombus, can form in an intact vessel. A
clot that breaks can travel though the bloodstream and clog
smaller blood vessels in various organs, thereby causing
heart attacks, strokes, pulmonary embolism, and kidney
failure.
4
Matching the ABO Group Allows Safe
Transfusions 296
• Red blood cells have various molecules called antigens on
their surfaces. Blood plasma contains antibodies to various
antigens circulating within it. During a transfusion, if red
blood cells containing a specific antigen are introduced into
a person who has antibodies to that specific antigen, the
antibodies attack and destroy the foreign red blood cells in
what is called a transfusion reaction.
• The most common blood group is the ABO group, where
red blood cells can have either A-antigens (type A), B-anti-
gens (type B), both antigens (type AB), or neither antigen
(type O); blood type testing (as shown) is based on these
characteristics.
ABO blood typing test • Figure 10.8a
Anti-A serum
Anti-B serum
Untreated
Treated with
Treated with
Blood
blood
anti-A serum
anti-B serum
type
AB
O
Blood type
>
DO
>
DO
O
Compatible donor blooc
types (no reaction)
A, O
B, O
A, B, AB
O
,
O
Incompatible donor
blood types (reaction)
B, AB
A, AB
-
A, B,
AB
A
B
• Within the Rh group, blood is either Rh-positive (has Rh anti-
gen) or Rh-negative (doesn't have Rh antigen). This group is
especially crucial to pregnant women who are Rh-negative
because Rh incompatibility between the mother's blood and
baby's blood can lead to hemolytic disease of the newborn.
In this condition, the mother's antibodies, produced during
the delivery of the first child, can attack the blood of a later
baby who has an incompatible blood type.
Summary 303
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