Platelets
are sometimes called thrombocytes, are tiny oval-shaped cells
made in the bone marrow. They help in the clotting process.
When a blood vessel breaks, platelets gather in the area and
help seal off the leak. Platelets survive only about 9 days
in the bloodstream and are constantly being replaced by new
cells.
Blood also contains important proteins called
clotting factors, which are critical to the clotting process.
Although platelets alone can plug small blood vessel leaks and
temporarily stop or slow bleeding, the action of clotting factors
is needed to produce a strong, stable clot.
Platelets
and clotting factors work together to form solid lumps to seal
leaks, wounds, cuts, and scratches and to prevent bleeding inside
and on the surfaces of our bodies. The process of clotting is
like a puzzle with interlocking parts. When the last part is
in place, the clot happens - but if only one piece is missing,
the final pieces can't come together.
When large blood vessels are severed (or cut),
the body may not be able to repair itself through clotting alone.
In these cases, dressings or stitches are used to help control
bleeding.
In addition to the cells and clotting factors,
blood contains other important substances, such as nutrients
from the food that has been processed by the digestive system.
Blood also carries hormones released by the endocrine glands
and carries them to the body parts that need them.