The blood consists of several types of leukocytes,
erythrocytes and platelet suspended in plasma. The cellular
elements of the blood are produced in extravascular tissues
such as the bone marrow and lymphoid tissues. After delivery
into the circulating blood ,the cellular elements may
function within the vascular system or after passing into
tissues. Blood elements have fixed lifespans and when they
die are removed from the circulation and replaced by new
cellular elements. The concentration of the various cellular
elements of the blood are maintained within strict limits.
Plasma constitutes greater than one-half of the blood
volume and is largely made up of water. In addition to
dissolved ions,plasma contains carrier proteins (such as
albumin, transferrin, haptoglobin, transcobalmin, and
lipoproteins), coagulation proteins, and immunoproteins
(immunoglobulin and complement) as well as growth factors,
interleukins and numerous other compounds.
Which of the following statements regarding plasma
carrier proteins is FALSE?
A. Transferrin transports iron to red blood cells
B. Albumin is the single most abundant plasma protein
C. The accumulation of copper results in the disease state
known as Wilson's disease
D. Alpha-1-antiprotease and alpha-2-macroglobulin neutralize
proteolytic enzymes released from neutrophils
E. Haptoglobin binds and reduces methemoglobin
Blood* is separated into its major components by
centrifugation. The red blood cells are at the bottom. On
top of these is the buffy coat (a thin layer of white blood
cells and platelets) and the remaining plasma.
Separation of blood by centrifugation is the basis for
the HEMATOCRIT - the ratio of the volume of the erythrocytes
to that of the whole blood, expressed as a decimal fraction.
*Anticoagulated blood (the anticoagulant is usually EDTA
- a Ca++ chelator), prevents formation of a fibrin clot in
the tube. The protein, water and salts forced out from
between the fibrin strands by centrifugation is known as
The Hematocrit (Hct) is sometimes referred to as the
Packed Cell Volume or volume of packed red cells. A spun or
centrifuged Hct contains a small (2%) amount of trapped
plasma between red cells.
Estimate the Hct for the microhematocrit shown on the
Normal Hct Values:
.42 - .54 *
.37 - .44 *
.53 - .68
.30 - .38
.37 - .44
* known approximate range
The Hct varies with age and sex.
Right, the Hct you estimated from the previous card was
about 0.45 !
Why is the normal adult Hct generally in the range of .40
- .45 ?
A. maximum erythroid cell production
B. optimal O2 carrying capacity and serum viscosity
C. hemoglobin threshold exceeded past 0.45
D. all of the above
E. none of the above
What is the origin of the cellular elements of the blood
? All blood cells appear to originate from a common
progenitor cell or pluripotent. This cell matures into cells
that are committed to one or another of the major cell lines
(committed stem cell). Purported stem cells can be recogized
only by immunologic means as morphologically they resemble
immature lymphocytes. Stem cells are self-replicating in
that only one of the daughter cells differentiates. The
other remains a stem cell. Thus the number of stem cells
remains constant. Thus the number of stem cells remains
Most of the early hematopoietic development and
maturation takes place in the bone marrow. The marrow may be
considered a large organ weighing from 1600-3700 gr.
Hematopoiesis is found in only certain bones of which the
major sites are the vertebra, sternum, pelvis, ribs, skull,
scapula,and proximal long bones.
The bone marrow is made up of hematopoietic cells and
stromal cells including fat cells and fibrocytes, with
extracellular connective tissue, and sinusoidal and vascular
spaces. The normal marrow contains 30-70% hematopoietic
cells,while the rest is largely fat. In hematopoietically
active marrows the amount of fat decreases whereas the
inverse occurs in inactive marrows.
Approximately 70% of the marrow cells are myeloid and 25%
are erythroid. All stages of maturation are found in the
marrow but egress from the marrow is normally limited by
stage of development.
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