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RED BLOOD CELLS

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									Criminalistics         Name:_________________________________________ Per:___
H.O.-Red Blood Cells
        The trillions of cells that compose the human body rely on red
blood cells, a.k.a. erythrocytes to supply them with oxygen and help
direct the elimination of waste carbon dioxide gas. Red blood cells
have a unique structure and properties that allow them to fulfill these
crucial missions. Red blood cells (RBCs) are the primary cells in
human blood. They are biconcave discs, having a depressed center
on both sides. These depressed centers allow the cells to have
more cell membrane surface which can be exposed to diffusing oxygen while transiting the
lungs. This structure also allows them to be more flexible when negotiating tight passages.
        RBCs are about 7.8 micrometers in diameter (A micrometer is 1/1,000,000 of a meter).
They have a flexible nature that allows them to bend and bounce back their original shape.
This comes in handy when they must squeeze through the minute capillary alleyways
between cells in the tissues.

Hemoglobin
        Unlike most cells, mature RBCs
of humans don’t have nuclei,
mitochondria, or other organelles.
Instead, they are packed full of a
special substance called hemoglobin
(Hgb), a complex molecule composed
of protein and iron. Hgb is responsible
for picking up oxygen, which diffuses
across membranes in the small vessels
of the minute lung sacks called alveoli.
Hgb holds onto oxygen until it reaches
areas of the body where it is in low
concentration and then releases it to
diffuse into local tissues.
        RBCs are passive in nature,
being swept along by the blood. They
sustain their meager energy needs by a form of anaerobic respiration. Since they don’t have
mitochondria, there are no worries they might gobble up the oxygen they are charged with
transporting.

Management of Carbon Dioxide
       RBCs also contain an enzyme called carbonic anhydrase which takes carbon dioxide
and water and catalyzes the creation of a stable molecule called bicarbonate (HCO3-).
Bicarbonate dissolves much better than carbon dioxide in the fluid part of blood and great
quantities can be transported this way without needing to be in the small red blood cells.
       Bicarbonate is an important buffer for blood, keeping it at a stable pH of about 7.4.
Buffers can be thought of as chemical “shock absorbers.” They keep the fluid of the blood
from being too acidic or basic, maintaining an environment where cellular machinery works
best. When the bicarbonate dissolved in the blood arrives in the capillaries of the lungs it is
converted back to gaseous carbon dioxide by RBCs and then diffuses out into the lungs
where it is breathed out.
Structural Abnormalities of RBCs
       Sometimes structural changes occur in RBCs that indicate a possible pathological
condition. For instance, one may observe enlarged RBCs with folate or vitamin B12
deficiency (macrocytic anemia). Small RBCs
may be observed with iron deficiency or
chronic blood loss (microcytic anemia). Sickle
cell anemia is a condition where a genetic flaw
leads to defective hemoglobin that changes
shape under certain conditions. This shape
change induces the cell to lose its original
biconcave disc confirmation and take on a
more “sickled” appearance.

Transfer of CO2 into RBC and O2 into Tissues




         Above is a representation of the transport of CO2 from the tissues to the blood with
delivery of O2 to the tissues. The opposite process occurs when O2 is taken up from the
alveoli of the lungs and the CO2 is expelled. All of the processes of the transport of CO2 and
O2 are not shown such as the formation and ionization of carbonic acid in the plasma. The
latter is a major mechanism for the transport of CO2 to the lungs, i.e. in the plasma as HCO3–.
The H+ produced in the plasma by the ionization of carbonic acid is buffered by phosphate
(HPO42–) and by proteins. Additionally, some 15% of the CO2 is transported from the tissues
to the lungs as hemoglobin carbamate.

								
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