Blood Contents | MCAT 2015
Breakdown of Blood
• Blood is a homogenous mixture,
but when centrifuged, it separates
into 3 distinct layers:
o Hematocrit: red blood
cells (erythrocytes)
o Buffy coat: white blood
cells (leukocytes) and
platelets
o Plasma: water and its
many dissolved solute
White Blood Cells
• White blood cells carry no
hemoglobin and they do have
organelles
• Unlike red blood cells, white
blood cells are responsible for
protecting the body against
infection
• Leukocytes can be classified as
granulocytes or agranulocytes
o Depending upon the
granular or agranular
nature of their cytoplasm
The 3 Components of Centrifuged Blood
(a)
(b)
Granulocytes and Agranulocytes
Leukocytes can be classified as (a) granulocytes
or (b) agranulocytes, depending upon the
granular or agranular nature of their cytoplasm.
•
Solutes of the plasma may
include ions, proteins, urea, and
other organic/inorganic
compounds
Red Blood Cells
• The sole purpose of erythrocytes
is to carry hemoglobin
o So red blood cells serve
exclusively to shuttle
O2/CO2 around the body
• They have no organelles- not
even a nucleus
• Their plasma membrane will
wear out over time
o When this occurs, the cell
ruptures and is cleared
from circulation
•
•
•
•
The granulocytes are:
o Neutrophils
o Eosinophils
o Basophils
Granulocytes fight all infectious
agents indiscriminately, so they:
o Multiply rapidly in the
presence of an infection
o Die quickly after the
infection is gone
The agranulocytes are:
o Monocytes
o Lymphocytes
o Megakaryocytes
Agranulocytes target specific
infectious agents
o They stick around long
after an infection is gone
to ensure it doesn’t return
Erythrocytes are Hemoglobin Shuttles
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© 2017 J Co Review, Inc., Accessed by Guest on 06-14-2017
Blood Contents | MCAT 2015
Platelets
• Platelets are like small cells with
no nuclei, and they aid in blood
clotting
• When they encounter injured
endothelium, they become sticky
o And, they encourage
other platelets to become
sticky too
• The platelets form a “loose plug”
over the injured endothelium in
order to prevent blood loss
(a)
(b)
Formation of the Loose Plug
When (a) platelets in the blood encounter
ruptured endothelium, they become sticky and
(b) stick together, forming a loose plug over the
injury and preventing further blood loss.
•
•
•
•
Formation of the Tight Plug
After platelets have formed a loose plug,
prothrombin and fibrinogen come into the area.
Prothrombin is rendered to its active form,
thrombin, which oversees the polymerization of
fibrinogen into a mesh called fibrin. Fibrin joins
the platelet plug forming the tight seal.
Other Important Details
• Some other proteins in the blood
that you should know are:
o Albumin – a protein
shuttle that carries fatty
acids in the blood
o Immunoglobulins – also
called antibodies
More on these
later
• On a side note, it is also worth
knowing that all blood cells (both
erythrocytes and leukocytes) are
derived from stem cells in bone
marrow
o Bone marrow is a flexible
tissue at the center of
bone
Recall the proteins prothrombin
and fibrinogen, which are
developed in the liver
Prothrombin (a zymogen) enters
the scene and is activated to its
active form: thrombin
Thrombin then oversees the
polymerization of fibrinogen into
a mesh called fibrin
The fibrin mesh joins the platelet
plug to form a “tight plug”
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© 2017 J Co Review, Inc., Accessed by Guest on 06-14-2017