How is blood made?
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Blood in the Body
How Is Blood Produced?
Blood cells are produced in the bone marrow, a jellylike substance inside
the bones that is composed of, among other things, fat, blood, and special
cells that turn into the various kinds of blood cells. In children, the
marrow of most of the bones produces blood. But in adults, only the marrow
of certain bones -- the spine, ribs, pelvis, and some others -- continues
to make blood. Bone marrow that actively produces blood cells is called red
marrow, and bone marrow that no longer produces blood cells is called
All blood cells come from the same kind of stem cell, which has the
potential to turn into any kind of blood cell. These stem cells are called
pluripotential hematopoietic stem cells.
As the blood cells develop from the stem cells in the marrow, they seep
into the blood that passes through the bones and on into the bloodstream.
The different kinds of blood cells have different "life spans" -- red blood
cells last about 120 days in the bloodstream; platelets about 10 days; and
the various kinds of white blood cells can last anywhere from days to
The body has a feedback system that tells it when to make new red blood
cells. If bodily oxygen levels are low (as they would be if there are too
few red blood cells circulating), the kidneys produce a
Blood - Wikipedia, the free encyclopedia
** Blood **
From Wikipedia, the free encyclopedia
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For other uses, see Blood (disambiguation).
Human blood smear:
a â erythrocytes; b â neutrophil;
c â eosinophil; d â lymphocyte.
A scanning electron microscope (SEM) image of a normal red blood cell, a
platelet, and a white blood cell.
Red = oxygenated
Blue = deoxygenated
Human blood magnified 600 times
Frog blood magnified 600 times
Fish blood magnified 600 times
*Blood* is a bodily fluid in animals that delivers necessary substances
such as nutrients and oxygen to the cells and transports metabolic waste
products away from those same cells.
In vertebrates, it is composed of blood cells suspended in blood plasma.
Plasma, which constitutes 55% of blood fluid, is mostly water (92% by
volume),^ and contains dissipated proteins, glucose, mineral ions,
hormones, carbon dioxide (plasma being the main medium for excretory
product transportation), and blood cells themselves. Albumin is the main
protein in plasma, and it functions to regulate the colloidal osmotic
pressure of blood. The blood cells are mainly red blood cells (also called
RBCs or erythrocytes) and white blood cells, including leukocytes and
platelets. The most abundant cells in vertebrate blood are red blood cells.
These contain hemoglobin, an iron-containing protein, which facilitates
transportation of oxygen by reversibly binding to this respiratory gas and
greatly increasing its solubility in blood. In contrast, carbon dioxide is
almost entirely transported extracellularly dissolved in plasma as
Vertebrate blood is bright red when its hemoglobin is oxygenated. Some
animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen,
instead of hemoglobin. Insects and some mollusks use a fluid called
hemolymph instead of blood, the difference being that hemolymph is not
contained in a closed circulatory system
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