Erythrocytes and Platelets
Sickle Cell Anemia, Blood Smear.
Sickle cell anemia
is an autosomal recessive disorder character-
ized by the production of defective hemoglobins, which aggregate
and polymerize when deoxygenated. The red blood cells become
longer and curved, similar to a “sickle.” Sickle cells block blood
of the tissues and severe pain. Symptoms
and signs, which start in early childhood, include anemia, vasooc-
clusive complications, and chronic
. This dis-
ease is more common in people of African, Turkish, Arabian, and
Mediterranean ancestry. Dehydration, infection,
and decreased pH can trigger an onset. In a sickle cell patient, the
average life span of red blood cells is 17 days, as compared to 120
days in normal persons. Bone marrow transplants can cure a small
number of people.
forms are shown here.
red blood cells
Erythrocytes (red blood cells), blood smear.
are the most abundant cells in blood. They have a
disk appearance (Fig. 8-3), are
nuclei), and have no organelles after they mature. Here, red blood
cells are seen as
pink circles with pale centers
in a Wright stain.
Erythrocytes are produced in the red bone marrow and are trans-
ported into the blood circulation through the walls of sinusoidal
capillaries in the marrow. Their life span is about 120 days. Aged
erythrocytes are destroyed by macrophages in the spleen, liver, and
bone marrow. Erythrocytes contain highly concentrated hemoglo-
bin (Hb). They appear bright red in color when oxygen content is
high and are more purple when they are depleted of oxygen. Their
function is to transport oxygen to peripheral tissues and carry car-
bon dioxide out of tissues. Hemoglobin binds with oxygen to form
oxyhemoglobin when the O
level is high (lung) and binds with CO
to form carbaminohemoglobin when the CO
level is high (tissue).
Platelets (thrombocytes), blood smear.
, also called
, are very small, lens-shaped frag-
ments of cells. They have some functional characteristics of whole
cells, even though they do not have nuclei. Each platelet has a surface
membrane covering cytoplasm that contains microtubules, micro-
± laments, mitochondria, and several types of granules. The central
region where granules stain purple is termed the
peripheral region, which stains light blue, is called the
The two main types of granules in platelets are
). These play a role in the adhesion and
aggregation of platelets in blood coagulation. If damage occurs to
the vascular endothelium, platelets adhere to the vessel wall, releas-
ing granules and aggregating to stop bleeding.
The absence of alpha granules can cause
whereas reduced numbers or absence of delta granules will lead
storage pool def