The structure of red blood cells • Figure 10.2
RBC shape - Red blood cells
b. Hemoglobin molecule - Hemoglobin
can be recognized by their
consists of four peptide chains, each with
biconcave shape and red color.
an iron-containing center, or heme.
The RBC is filled with a protein called hemoglobin (he'-mo-GLO-
bin), which gives these cells their red color. Hemoglobin is an iron-
based protein that binds most of the oxygen and a small portion of the
carbon dioxide and allows the RBCs to transport these gases through
the blood (Figure 10.2).
The next major formed element is the platelet (PLAT-let)(see
Figure 10.1). Platelets are actually tiny fragments of larger cells
called megakaryocytes (meg-a-KAR-e-o-sits), found only in the red
bone marrow. Platelets consist of a little cytoplasm enclosed within a
piece of cell membrane. As you will see later, platelets are important
for blood clotting.
The last category of formed elements is white blood cells
(WBCs), or leukocytes (LOO-ko-sits). WBCs comprise less than
0.2% of the formed elements and are made up of five types of cells:
neutrophils (NOO-tro-fils), lymphocytes (LIM-fo-sits), monocytes
(MON-o-sits'), eosinophils (e'-o-SIN-o-fils), and basophils (BA-so-
fils)(see Figure 10.1). WBCs are very different in appearance from
one to another and from RBCs and platelets. One major distinction
is that, unlike RBCs and platelets, WBCs have nuclei. Each type of
WBC has characteristic features when stained and viewed under a
microscope. As a result, they can be classified as either
g ra n u la r
ing cytoplasmic granules) or
(no cytoplasmic granules) (Fig-
ure 10.3). All white blood cells are involved in protecting the body by
engulfing invading bacterial cells or viruses, releasing chemicals that
initiate immune responses, or producing antibodies. You will learn
more about these functions in Chapter 12.
are the three major functions of blood?
is blood plasma different from water?
type of formed element consists of pieces of an-
A p p e aran c e o f b lo o d cells
in a b lo o d sm e a r • Figure 10.3
Blood smear stained with W right’s stain -
Note that there are few white blood cells compared
to platelets and red blood cells.
white blood cells
white blood cells -
Single nucleus, no cytoplasmic granules
290 CHAPTER 10
The Cardiovascular System: Blood