4 Components of Blood
The main components of blood include
Plasma
Red blood cells
White blood cells
Platelets
Plasma
Plasma is the liquid component of blood, in which the red
blood cells, white blood cells, and platelets are suspended. It constitutes
more than half of the blood's volume and consists mostly of water that contains
dissolved salts (electrolytes) and proteins. The major protein in plasma is
albumin. Albumin helps keep fluid from leaking out of blood vessels and into
tissues, and albumin binds to and carries substances such as hormones and
certain drugs. Other proteins in plasma include antibodies (immunoglobulins),
which actively defend the body against viruses, bacteria, fungi, and cancer
cells, and clotting factors, which control bleeding.
Plasma has other functions. It acts as a reservoir that can
either replenish insufficient water or absorb excess water from tissues. When
body tissues need additional liquid, water from plasma is the first resource to
meet that need. Plasma also prevents blood vessels from collapsing and clogging
and helps maintain blood pressure and circulation throughout the body simply by
filling blood vessels and flowing through them continuously. Plasma circulation
also plays a role in regulating body temperature by carrying heat generated in
core body tissues through areas that lose heat more readily, such as the arms,
legs, and head.
Red Blood Cells
Red Blood Cells
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Red blood cells (also called erythrocytes) make up about 40%
of the blood's volume. Red blood cells contain hemoglobin, a protein that gives
blood its red color and enables it to carry oxygen from the lungs and deliver
it to all body tissues. Oxygen is used by cells to produce energy that the body
needs, leaving carbon dioxide as a waste product. Red blood cells carry carbon
dioxide away from the tissues and back to the lungs. When the number of red
blood cells is too low (anemia), blood carries less oxygen, and fatigue and
weakness develop. When the number of red blood cells is too high
(erythrocytosis, as in polycythemia vera), blood can become too thick, which
may cause the blood to clot more easily and increase the risk of heart attacks
and strokes.
White Blood Cells
White blood cells (also called leukocytes) are fewer in
number than red blood cells, with a ratio of about 1 white blood cell to every
600 to 700 red blood cells. White blood cells are responsible primarily for
defending the body against infection. There are five main types of white blood
cells.
White Blood Cells
White Blood Cells
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Neutrophils, the most numerous type, help protect the body
against infections by killing and ingesting bacteria and fungi and by ingesting
foreign debris.
Lymphocytes consist of three main types: T cells (T
lymphocytes) and natural killer cells, which both help protect against viral
infections and can detect and destroy some cancer cells, and B cells (B
lymphocytes), which develop into cells that produce antibodies.
Monocytes ingest dead or damaged cells and help defend
against many infectious organisms.
Eosinophils kill parasites, destroy cancer cells, and are
involved in allergic responses.
Basophils also participate in allergic responses.
Some white blood cells flow smoothly through the
bloodstream, but many adhere to blood vessel walls or even penetrate the vessel
walls to enter other tissues. When white blood cells reach the site of an infection
or other problem, they release substances that attract more white blood cells.
The white blood cells function like an army, dispersed throughout the body but
ready at a moment's notice to gather and fight off an invading organism. White
blood cells accomplish this by engulfing and digesting organisms and by
producing antibodies that attach to organisms so that they can be more easily
destroyed.
When the number of white blood cells is too low
(leukopenia), infections are more likely to occur. A higher than normal number
of white blood cells (leukocytosis) may not directly cause symptoms, but the
high number of cells can be an indication of an underlying disorder such as an
infection, inflammatory process, or leukemia.
Platelets
Types of Blood Cells
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Platelets (also called thrombocytes) are cell-like particles
that are smaller than red or white blood cells. Platelets are fewer in number
than red blood cells, with a ratio of about 1 platelet to every 20 red blood
cells. Platelets help in the clotting process by gathering at a bleeding site
and clumping together to form a plug that helps seal the blood vessel. At the
same time, they release substances that help promote further clotting. When the
number of platelets is too low (thrombocytopenia), bruising and abnormal
bleeding become more likely. When the number of platelets is too high
(thrombocythemia), blood may clot excessively and can block blood vessels
causing disorders such as a transient ischemic attack. When the number of
platelets is extremely high, the platelets can absorb clotting proteins and
paradoxically cause bleeding.