Histology
Blood, Bone marrow
Hematopoiesis
By- Dr.Elham
Majed
TUCOM
Blood is a special type of connective tissue
composed of plasma and formed elements,
erythrocytes, leukocytes and platelets
Erythrocytes are the most abundant blood cells
(about 700 erythrocytes for every 1 leukocyte).
Erythrocytes are smaller than leukocytes. An
erythrocyte has no nucleus (it is ejected as the cell
develops). Erythrocytes deliver O
2
to the cells ,
Hemoglobin molecules within erythrocytes bind
O
2
when erythrocytes pass through the high
O
2
environment of lung capillaries. Hemoglobin
molecules release O
2
when erythrocytes pass
through the low O
2
environment of capillaries in the
rest of the body
.
Platelets are pinched-off bits of cytoplasm (of a bone marrow
cell called a megakaryocyte) enclosed in plasma membrane.
Platelets devoid of nucleus and contain various substances
that contribute to blood clotting
.
The leukocytes have important roles in defending the body
against infection by microorganisms. Certain leukocytes
(and cells derived from leukocytes) phagocytize and thereby
recycle worn or dead body cells and cell fragments.
Leukocytes perform most of their functions after they leave
the blood and enter tissues. There are five types of
leukocytes each with a different appearance and function
.
Neutrophils are the most abundant leukocyte (approximately
65% of the leukocytes). Neutrophils have a lobed nucleus
and cytoplasm containing inconspicuous reddish-purple
granules
.
Lymphocytes (about 25% of leukocytes) are the smallest of
the leukocytes, just a bit larger than erythrocytes. A
lymphocyte has a large spherical nucleus and a thin rim of
blue-gray cytoplasm
.
Monocytes (about 6% of leukocytes) are the
largest leukocytes and may show an irregular
shape in blood smears. Monocytes typically have
an indented nucleus and blue-gray cytoplasm
.
Eosinophil's (about 3% of leukocytes) have red
granules in the cytoplasm and typically have a
two-lobed nucleus
.
Basophils (less than 1% of leukocytes) have
prominent dark purple granules in the cytoplasm
which partially obscure the lobed nucleus
.
Hematopoiesis
Hematopoiesis is the formation of new blood cells. In this
process, hematopoietic stem cells are processed, transformed,
developed and differentiated into different type of cells to serve
their specific purposes according to their location and
structural build. All type of blood cells are derived from one
immature cell which is the hematopoietic stem cells (HSCs). If
we are to take a cross section of our bone, we can notice that
there is a central cavity
.
And in this cavity we can find the bone marrow. Bone marrow is
the major site for hematopoiesis. So obviously, there’s a large
amount of HSCs in this area. This is where the genetic
structures of each HSCs are modified and differentiated by
changing the protein components of our HSCs
.
After that the production is transferred to our liver. And then
when our bone matures it is then transitioned to our bone
marrow and thymus gland
..
hematopoiesis = hemopoiesis - The
formation and development of red ,
white blood cells and platelets involving
proliferation and differentiation from
specific stem cell types; occurs in the
red bone marrow in adults, in embryos,
other tissues such as the liver also
participate
.
red bone marrow - The type of marrow
tissue found in spongy bone and marrow
cavities where the various blood stem
cells reside and where new red blood
cells, white blood cells, and platelets are
produced for release into the circulation
.
yellow bone marrow - The type of marrow
tissue found in spongy bone and marrow
cavities where adipose tissue
predominates; a storage depot for fats
.
