Blood
Blood is a liquid
connective tissue. It is composed of a
variety of cells circulating in a fluid, plasma. We are not interested in plasma in this
lesson, only in the cells, both white and red blood cells. Blood cells are in three functional classes:
red blood cells (erythrocytes), white blood cells (leukocytes) and platelets
(thrombocytes). All three are formed in
the bone marrow but have vastly different appearances and functions.
Red blood cells
(RBC’s) are the most numerous cell type in the blood (4.8-5.4 million RBC’s/mL of blood).
The cells are modified structurally to carry oxygen. The cells are biconcave disks approximately
8µm in diameter (a doughnut without a hole) with no nucleus or metabolic
machinery. The absence of cellular
organelles allows the internal space of the cell to be available for O2
carrying. The interior of the RBC is filled
with Hemoglobin (Hgb), a protein that functions primarily to carry O2. A
typical
RBC
has approximately 280 million Hgb molecules in
it due to the lack of cellular organelles.
White blood cells
(WBC’s) are much less numerous than RBC’s (5,000 - 10,000 WBC’s/mL
blood) with a RBC/WBC ratio of approximately 700:1. WBC’s work to protect the body from
infection. WBC’s
are divided into two main groups based on cytoplasmic appearance: agranular
leukocytes - lymphocytes and monocytes which have relatively clear cytoplasm;
and
granular
leukocytes – neutrophils, eosinophils, and basophils whose cytoplasm is filled with granules.
Granular Leukocytes
Neutrophils The
most abundant granulocyte, and most abundant WBC, is the
neutrophil comprising
60-70% of all WBC’s. They
are approximately 10-12 µm diameter with very
fine, pale lilac granules in the cytoplasm. The
nucleus has from 2-5 finely connected nuclear
lobes that are rarely uniform in size. The multiple lobed nucleus and lightly stained cytoplasm are the
most identifiable characteristics of the this cell. Neutrophils respond
rapidly by chemotaxis to bacterial damage. They
then phagocytize pathogens and release lysozymes,
strong oxidants and defensins to help fight the infection. |
 |
Eosinophils Eosinophils represent only 2-4% of all WBC’s. They are similar
in size to neutrophils, 10-12 µm diameter, with
red/orange, large uniform granules, that do not block the nucleus. The nucleus usually has 2 but may have 3 connected
nuclear lobes that tend to be more rounded and uniform than found in
neutrophils. The red/orange color and
more uniformly shaped lobed nucleus are the keys to identifying this
cell. Eosinophils combat
histamine in allergic responses, phagocytize antigen-antibody complexes
and destroy some parasitic worms. |
The least common WBC is the basophil comprising only 0.5-1% of all WBC’s. Basophils are 8-10 µm diameter with large blue-black round granules in the cytoplasm that block the bilobed nucleus. The dark granules are the most easily identifiable characteristic of this cell. Basophils exit capillaries and enter tissue fluids where they release heparin, histamine and serotonin during hypersensitivity (allergic) reactions to stimulate inflammation. Click image to enlarge. |
 |
Lymphocytes Lymphocytes make up 20-25% of all WBC’s. These cells vary in size with small lymphocytes being 6-9µm and large lymphocytes 10-14µm in diameter. The nucleus stains dark and is round or slightly indented with the cytoplasm appearing as a rim around the nucleus. The round, uniform nucleus and small amount of cytoplasm surrounding it are the best identifying characteristics for this cell. Lymphocytes are involved in the specific immune response including antigen-antibody reactions. Click image to enlarge. |
 |
Monocytes Monocytes comprise 3-8% of all WBC’s. They are the largest of the WBC’s, 12-20 µm in diameter. The nucleus is indented or kidney shaped, not
rounded, and surrounded by foamy cytoplasm. Their
size is the most easily identifiable characteristic. Monocytes are
slow to respond to infection but arrive in larger numbers. When
stimulated they enlarge and differentiate into wandering macrophages
that clean up cellular debris and microbes following infection. |
 |
Thrombocytes Thrombocytes, or platelets, are numerous (150,000-400,000
platelets/mL blood) with
a short 5-9 day life span. These
cell fragments are small (2-4 µm diameter) with many vesicles and no
nucleus. They often appear as spots or "dirt" between
the RBC's. Platelets
function to plug small holes in vessels and stop bleeding. The
granules contain many factors involved in blood clotting, including
clotting
factors, platelet derived growth factor (PDGF), Ca++, ADP,
ATP, Thromboxane A2, vasoconstrictors,
and clot promoting enzymes. |
 |
Blood Cell Counts
A common
physiological assessment of blood is the determination of the number of blood
cells present. In this lab, you will
perform two types of cell counts: 1) Hematocrit – a
measurement of the number of red blood cells currently in the blood; and 2) Differential
white blood cell count – determination of the percentage of each type of white
blood cell in the blood.
You will be assigned
a number between 1 and
24. This number will determine the set
of slides you use for your cell counts.
Record this number on your Blood Lab Worksheet. Use the same number
for
both
the
red
and
white
blood
cell
counts. At the end of these instructions
there is a link to the Cell count home. Once you have accessed the Cell
count home use the pull-down menu under your assigned number
to
select
either
the red (Hematocrit) or white (Differential
white blood cell) blood cell count option.
Hematocrit
Protocol
Red blood cell counts
employ a special microscope slide called a hemocytometer.
A hemocytometer is a special glass slide with a small chamber, or counting
area,
for
counting
cells
in a given volume. The counting area has a grid on it to allow for easier
counting of the cells. This technique allows
for
an
estimation
of
the
total
number
of
red
blood
cells
present
in
a sample. The large numbers of red blood cells present
in blood (discussed above) make it impossible to
count
every cell. Instead, you will use a simulated hemocytometer
to
estimate
the number of RBC’s present.
After you
select your "Red blood cell
count”, you will be
presented with 4 images, or "slides", of blood cells. Each image has a grid superimposed on it, much
like
the grid
found on a hemocytometer slide. The grid divides the area to be counted into
16 smaller sections, allowing
you
to
count
the
red
blood
cells
in
smaller, manageable groups. Count all of the red blood cells in each of
the
grid
squares. DO
NOT count a cell if ANY part of
the cell touches ANY part of the OUTER grid
lines. If
a cell touches or overlaps any of the INNER grid lines, count
the cell but be sure
to
count
it only once. There may be white blood cells present in these
samples. The white blood cells are not to be counted.
Count only the red blood cells.
Count and record
the number of red blood cells in each square and, ultimately, the entire
area of the grid. Record
each of your
cell counts in the table on the Blood Lab Worksheet. Add
up your counts from all 4 slides and record the total on the "Total" line of
the worksheet. Once
you have added all of your counts,
multiply your total by 2500 (Note: DO
NOT use 10,000 as indicated in the lab manual). Record this value, your RBC estimate, in the appropriate blank and
answer
the following questions.
Question
1
As
described earlier, assuming a ratio of 700 RBC’s to 1 WBC, use your hematocrit
count to determine the number of white blood cells you would expect to see in
this same sample of blood. Record this
on the worksheet.
Question
2
Using
the information in Chapter 19 of your textbook, identify a condition that might
generate an abnormally high or low hematocrit count. Explain why this effect occurs.
Differential White Blood Cell Count Protocol
Select the
appropriate “White blood cell count”. You
will be presented with a series of blood smear slides. For each slide, you will identify and record
the number of each of the 5 different types of leukocytes present.
Record
your white
cell count data on Blood Lab Worksheet.
For each slide,
identify the WBC’s present and place a tick mark
next to the name of the white blood cell you see. When
you have counted 100 TOTAL white
blood cells (all WBC’s together, NOT 100 of each type of WBC) STOP! Count the number of ticks for each cell type
and determine the percentage of each type of leukocyte present in your
sample. Record the percentages
in the table on your worksheet.
Question
Using
the information in Chapter 19 of your textbook, identify two (2) types of
disorders that would generate an abnormal differential white blood cell
count. In each case, specify which white
blood cells are affected and how they are affected.