Webster's New World Medical Dictionary

Bloch-Sulzberger syndrome
See 
incontinen-
tia pigmenti.
blocker, beta
See 
beta blocker.
blood
The red fluid in the body that contains
white and red blood cells, platelets, proteins, and
other elements. Blood is transported throughout the
body by the circulatory system. Blood flows in two
directions: away from the heart (arterial blood) and
toward the heart (venous blood). Arterial blood has
a high concentration of oxygen and nutrients for
body tissues, and venous blood is the means by
which carbon dioxide is transported to the lungs for
removal from the body. See also 
blood cell.
blood cell
One of several different types of cells
that make up the blood. The red blood cells (ery-
throcytes) contain hemoglobin, which carries oxy-
gen in the blood. The white blood cells (leukocytes)
are a blood-borne part of the immune system. The
platelets help blood to clot. Together, these three
types of cells make up about half of the volume of
blood. The remainder is made up of plasma. See
also 
erythrocyte; leukocyte; plasma; platelet.
blood clot
A mass of coagulated blood. A blood
clot can block a major blood vessel, causing stroke
or other problems.
blood clot, estrogen-associated
A blood clot
associated with estrogen therapy. Blood clots are
occasional but serious side effects of estrogen ther-
apy. They occur most frequently with high doses of
estrogen. Cigarette smokers on estrogen therapy are
at a higher risk for blood clots than nonsmokers
are. Therefore, patients requiring estrogen therapy
are strongly encouraged to quit smoking. See also
estrogen; estrogen replacement therapy.
blood coagulation
The aggregation of blood
platelets and other blood elements to form a semi-
solid clot. Coagulation occurs under the influence
of the clotting factors fibrinogen, prothrombin, and
thrombin, which are normally activated in response
to injury. Working together, these substances
thicken the blood and produce fibrin, a substance
that closes off the wound. When blood coagulates
abnormally, dangerous blood clots can enter the
bloodstream.