Vertebrate erythrocytes
Erythrocytes consist mainly of hemoglobin, a complex
molecule containing heme groups whose iron molecules
temporarily link to oxygen molecules in the lungs or
gills and release them throughout. Hemoglobin also carries
some of the waste product carbon dioxide back from the
tissues. (In humans, less than of thetotal oxygen, and
most of the carbon dioxide, are held in solution in
the blood plasma). A related compound, myoglobin, acts
to store oxygen in muscle cells.The color of erythrocytes
is to the heme group of hemoglobin. Individual RBCs
are straw-colored, but in the aggregate they appear
bright-red if the hemoglobin is bound to oxygen, and
bluish-purple if not. The keeping of oxgen-binding proteins
in cells rather than having them dissolved in body fluid
was an important step in the evolution of vertebrates;
it allows for less viscous blood and longer transport
ways of oxygen.
Mammalian erythrocytes
Erythrocytes in mammals are anucleate when mature, meaning that
they don't have a cell nucleus and thus no DNA. The erythrocyts
of nearly all other vertebrates have nuclei; the only known exception
are salamanders of the Batrachoseps genus.Erythrocytes also lose
their other organelles including their mitochondria and produce
energy by fermentation, via glycolysis of glucose followed y lactic
acid production. Like most cell types, red cells do not have an
insulin receptor and thus glucose uptake is not regulated by insulin.ammalian
erythrocytes have a biconcave shape: flattened and depressed in
the center. This shape optimizes cell for the exchange of oxygen
with its surroundings. The cells are flexible so as to fit through
tiny capillaries, where they release their oxygen lad. Erythrocytes
are circular, except in the camel family Camelidae, where they are
oval.In large blood vessels, red blood cells sometimes occur as
a stack, flat side next to flat side. This isknown as rouleaux formation,
and it occurs more often if the levels of certain serum proteins
are elevatance during inflammation.The spleen acts as a of red blood
cells, but this effect is somewhat limited in humans. In some other
mammals such as dogs and horses, the spleen sequesters large numbers
of red blood cells that are dumped into the blood during times of
exertion stress, yielding a higher oxygen transport capacity.
Human erythrocytes
The diameter of a typical human erythrocyte is ; they are thus much
smaller than most other human cells. A typical erythrocyte contains
about million hemoglobin molecules, with each carrying four heme
groups.Adult humans have roughly red blood cells at any given time
(women have about 4 million to million erythrocytes per cubic millimter
of blood ad men about 5 million to people living at high ltitudes
with low oxygen concentration will have more. Red blood cells are
thus much more common than the other blood particles: there are
about 4,000–11,000 white blood cells and about platelets in
a cubic millimeter of human blood. The red blood cells store collectively
about 3.5 grams of iron; that's more than five times the iron stored
by all the other tissues combined.
The process by which red blood cells are produced
is called erythropoiesis. Erythrocytes are continuously being produced
in the red bone marrow of large bones. In the embryo, the liver
is the main site of red blood cell production The production can
be stimulated by the hormone erythropoietin , which is used for
doping in sports. Erythrocytes develop in about 7 days and live
a total of about120 days. The aging cells swell up to a sphere-like
shape and are engulfed by phagocytes, destroyed and t materials
are released into the blood. The main sites of destruction are the
liver and the spleen. The heme constituent of hemoglobin is eventually
excreted as bilirubin.The blood types of humans due to variations
in surface glycoproteins of erythrocytes.
Red blood cells can be separated from blood plasma
by centrifugation. During plasma donation, the red blood
cells are pumped back into the body right away, and
the plasma is collected. Some athletes have tried to
improve their performance by doping teir blood: first
about 1 liter of their blood is extracted, then the
red blood cells are isolated, frozen and stored, to
be reinjected shortly before the competition. (Red blood
cells can be conserved for 5 weeks at This practice
is hard to detect but may endanger the human cardiovascular
system which is not equipped to deal with blood of the
resulting higher viscosity.
Diseases and diagnostic tools
Affected by Sickle-cell disease, red blood cells alter shape and
threaten to damage internal organs.Blood diseases involving the
red blood cells include:
Anemias or anaemias are diseases characterized by
low oxygen transport capacity of the blood, because
of low red cell count or some abnormality of the red
blood cells or the hemoglobin. Iron deficiency anemia
is the most common anemia; it occurs when the dietary
intake or absorption of iron is insufficient, and hemoglobin,
which contains iron, cannot be formed
Sicklecell disease is a genetic disease which leads
to mis-shaped red blood cells.
Thalassemia is a genetic disease that results in the
of abnormal hemoglobin molecules.
Spherocytosis is a genetic disease that causes a defectin
the red blood cell's cytoskeleton, causing the RBCs
to be small, sphere-shaped, and fragile instead of donut-shaped
and flexible.
Pernicious anemia is an autoimmune disease where the
body lacks intrinsic factor, required to absorb vitamin
B12 from food. Vitamin B12 is needed for the production
of hemoglobin.
Aplastic anemia is caused by the inability of the bone
marrow to produce blood cells.
Hemolysis is the general term for excessive breakdown
of red blood cells. It can have several causes.
The malaria parasite spends part of its life-cycle in
red blood cells, feeds on their hemoglobin and then
breaks them apart, causing fever. Both sickle-cell disease
and thalassemia are more common in malaria areas, because
these mutations convey some protection against the parasite.
Polycythemiasre diseases characterized by a surplus
of red bood cells. The increased viscosity of the blood
can cause a number of symptoms.
In polycythemia vera the increased number of red blood
cells results from an abnormality in the bone marrow.
Several blood tests involve red blood cells, including the RBC count
the number of red blood cells per volume of blood) and the hematocrit
(percentage of blood volume occupied by red blood cells The blood
type needs to be determined
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