BSC 215 Lecture Notes - Lecture 39: Hematopoietic Stem Cell, Pernicious Anemia, Leukopoiesis

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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
colonystimulating 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:
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Document Summary

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, 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.

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