Page 50 - Clinical Hematology Atlas

34 SECTION TWO HEMATOPOIESIS

latelets arise from the megakaryocyte. Megakaryocytes are among the largest cells in the
Pbody and mature by a unique process called endomitosis. In endomitosis, the nucleus is
duplicated but there is no cell division, resulting in a polyploid cell. Megakaryocyte nuclei
may have from 2 to 32 lobes and, in unusual cases, may have up to 64 lobes. Megakaryocytes
develop copious cytoplasm, which differentiates into platelets. Platelets have several types of
granules that can be visualized by electron microscopy. The granules are highly specialized.
Refer to a hematology textbook for further discussion.

FIGURE 4–1 Megakaryocyte sequence—
S megakaryoblast MK-I.
T Multipotent
E hematopoietic stem cell
M

P
R Common myeloid
O progenitor
G
E
N
I Megakaryocyte-erythrocyte
T progenitor
O
R

Megakaryoblast
MK-I

P
R
E Promegakaryocyte
C MK-II
U
R
S
O
R

Megakaryocyte
MK-III

P
E
R
I B
P L
H O Platelets
E O
R D
A
L

All photomicrographs are 31000 original magnification with Wright-Giemsa staining unless stated
otherwise.