Blood Formation
• Hemopoiesis ( hematopoiesis) is the process that produces the
formed elements of the blood.
• Hemopoiesis takes place in the red bone marrow found in the
epiphyses of long bones (for example, the humerus and femur), flat
bones (ribs and cranial bones), vertebrae, and the pelvis.
• Within the red bone marrow, hemopoietic stem cells (
hemocytoblasts) divide to produce various “blast” cells.
• Each of these cells matures and becomes a particular formed
element.
, Erythropoiesis
• Erythropoiesis, the process of making erythrocytes, begins with the
formation of proerythroblasts from hemopoietic stem cells.
• Over three to five days, several stages of development follow as
ribosomes proliferate and hemoglobin is synthesized.
• Finally, the nucleus is ejected, producing the depression in the center
of the cell.
• Young erythrocytes, called reticulocytes, still containing some
ribosomes and endoplasmic reticulum, pass into the bloodstream and
develop into mature erythrocytes after another one or two days.
,Erythropoietin
• Erythropoietin (EPO), a hormone produced mostly by the kidneys,
stimulates bone marrow to produce erythrocytes (stimulates
erythropoiesis).
• When inadequate amounts of oxygen are delivered to body cells, a
condition called hypoxia, the kidneys increase EPO secretion, which in turn
stimulates an increase in erythrocyte production.
• The average production rate of erythrocytes in healthy individuals is two
million cells per second.
• Normal production requires adequate amounts of iron, vitamin B 12, and
folic acid.
• Vitamin B 12 and folic acid are necessary for the proper development of
DNA in the erythroblasts.
• This DNA is responsible for the organization of the heme molecule of which
iron will become a component.
• Proper DNA development is also necessary for erythroblast reproduction.
• A lack of either vitamin B 12 or folic acid can result in pernicious anemia.
, Leukopoiesis
• Leukopoiesis, the process of making leukocytes, is
stimulated by various colony‐stimulating factors (CSFs)
which are hormones produced by mature white blood
cells.
• The development of each kind of white blood cell
begins with the division of the hemopoietic stem cells
into one of the following “blast” cells:
Myeloblasts divide to form eosinophilic, neutrophilic, or
basophilic myelocytes, which lead to the development of
the three kinds of granulocytes.
Monoblasts lead to the development of monocytes.
Lymphoblasts lead to the development of lymphocytes.
• Hemopoiesis ( hematopoiesis) is the process that produces the
formed elements of the blood.
• Hemopoiesis takes place in the red bone marrow found in the
epiphyses of long bones (for example, the humerus and femur), flat
bones (ribs and cranial bones), vertebrae, and the pelvis.
• Within the red bone marrow, hemopoietic stem cells (
hemocytoblasts) divide to produce various “blast” cells.
• Each of these cells matures and becomes a particular formed
element.
, Erythropoiesis
• Erythropoiesis, the process of making erythrocytes, begins with the
formation of proerythroblasts from hemopoietic stem cells.
• Over three to five days, several stages of development follow as
ribosomes proliferate and hemoglobin is synthesized.
• Finally, the nucleus is ejected, producing the depression in the center
of the cell.
• Young erythrocytes, called reticulocytes, still containing some
ribosomes and endoplasmic reticulum, pass into the bloodstream and
develop into mature erythrocytes after another one or two days.
,Erythropoietin
• Erythropoietin (EPO), a hormone produced mostly by the kidneys,
stimulates bone marrow to produce erythrocytes (stimulates
erythropoiesis).
• When inadequate amounts of oxygen are delivered to body cells, a
condition called hypoxia, the kidneys increase EPO secretion, which in turn
stimulates an increase in erythrocyte production.
• The average production rate of erythrocytes in healthy individuals is two
million cells per second.
• Normal production requires adequate amounts of iron, vitamin B 12, and
folic acid.
• Vitamin B 12 and folic acid are necessary for the proper development of
DNA in the erythroblasts.
• This DNA is responsible for the organization of the heme molecule of which
iron will become a component.
• Proper DNA development is also necessary for erythroblast reproduction.
• A lack of either vitamin B 12 or folic acid can result in pernicious anemia.
, Leukopoiesis
• Leukopoiesis, the process of making leukocytes, is
stimulated by various colony‐stimulating factors (CSFs)
which are hormones produced by mature white blood
cells.
• The development of each kind of white blood cell
begins with the division of the hemopoietic stem cells
into one of the following “blast” cells:
Myeloblasts divide to form eosinophilic, neutrophilic, or
basophilic myelocytes, which lead to the development of
the three kinds of granulocytes.
Monoblasts lead to the development of monocytes.
Lymphoblasts lead to the development of lymphocytes.
