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How long can most formed elements of the blood last?
hours, days or weeks
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How often do most formed elements need to be replaced?
continually
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What regulate the total number of RBC and platelets in circulation?
negative feedback systems
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What does the abundance of the different types of WBCs depend on?
It varies in response to challenges by invading pathogens and other foreign antigens
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define hemopoiesis
the process by which the formed elements of blood develop
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What is another name for hemopoiesis?
hematopoiesis
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when does hemopoiesis start?
before birth it first occurs in the yolk sac of an embryo
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where does hemopoiesis continue thru the formation of the fetus?
in the liver, spleen, thymus and lymph nodes
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During the last 3 months before what takes over the role of hemopoiesis?
Red bone marrow
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What is red bone marrow?
a highly vascularized connective tissue located in the microscopic spaces between trabeculae of spongy bone tissue
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Where is red bone marrow found?
It is present chiefly in bones of the axial skeleton, pectoral and pelvic girdles, and the proximal epiphyses of the humerus and femur
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About 0.05–0.1% of red bone marrow cells are derived from mesenchyme and are called
pluripotent stem cells
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What kinds of cells have the capacity to develop into many different types of cells?
pluripotent stem cells or hemocytoblasts
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When you are a newborn, all your bone marrow is ____ and is active in blood cell ____
red
production
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When we age our red marrow in the medullary cavity of long bones becomes inactive and is replaced by
yellow bone marrow
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Under certain conditions, can yellow marrow ever turn into red marrow?
Yes...then red marrow can make more yellow marrow
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How are some disorders like leukemia and severe anemias diagnosed?
a sample of red bone marrow is taken and examined
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What are the technical terms for the examination of bone marrow?
bone marrow aspiration and bone marrow biopsy
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Where are the bone marrow aspiration or bone marrow biopsys taken from?
They are usually taken from the iliac crest of the hip bone, although sometimes also taken from the sternum
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Where are bone marrow smaples taken from in children?
a vertebra or tibia
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What happens to the bone marrow after it is aspirated from the bone?
The tissue or cell sample is then sent to a pathology lab for analysis. Specifically, laboratory technicians look for signs of neoplastic (cancer) cells or other diseased cells to assist in diagnosis.
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How do stem cells function and give rise to?
Stem cells in red bone marrow reproduce themselves, proliferate, and differentiate into cells that give rise to blood cells, macrophages, reticular cells, mast cells, and adipocytes. Some of the stem cells can also form osteoblasts, chondroblasts, and muscle cells, and someday may be used as a source of bone, cartilage, and muscular tissue for tissue and organ replacement.
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What do reticular cells produce?
reticular fibers
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What do reticular fibers do?
form the stroma (framework) that supports red bone marrow cells
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What happens after blood cells are produced in red bone marrow?
they enter the bloodstream through sinusoids (also called sinuses), enlarged and leaky capillaries that surround red bone marrow cells and fibers
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Formed elements do not divide once they leave red bone marrow, with what exception?
with the exception of lymphocytes
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In order to form blood cells, pluripotent stem cells in red bone marrow produce two further types of stem cells, which have the capacity to develop into several types of cells. They are called:
myeloid stem cells and lymphoid stem cells
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Where do myeloid stem cells begin and give rise to?
They begin their development in red bone marrow and give rise to red blood cells, plateslets, monocytes, neutrophils, eosinphils, and basophils
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Where do lymphoid stem cells begin and what do they give rise to?
they begin their development in red bone marrow but complete it in lymphatic tissues; they give rise to lymphocytes
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Although the various stem cells have distinctive cell identity markers in their plasma membranes, they cannot be distinguished histologically and resemble...
lymphocytes
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During hemopoiesis, some of the myeloid stem cells differentiate into ______ ____
progenitor cells
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do some myeloid stem cells and the lymphoid stem cells develop directly into precursor cells?
yes
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Progenitor cells are no longer capeable of ___ ____ and are committed to giving rise to more specific elements of blood
reproducing themselves
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what are some progenitor cells known as?
colongy forming units (CFUs)
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What does the abbreviation that follows the CFU designation mean?
it indicates the mature elements in blood that progenitor cells will produce (CFU-E ultimately produces erythrocytes)
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What does CFU-Meg produce?
megakaryocytes, the source of platelets
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progenitor cells resemble ___ and cannot be distinguished by their microscopic appearance alone
lymphocytes
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the next generation of cells after progenitor cells are called...
precursor cells
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what are precursor cells also known as?
blasts
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Over several cell divisions, what develop into the actual formed elements of blood?
precursor cells, aka blasts
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Do precursor cells have recognizable microscopic appearances?
yes
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What hormones regulate the differentiationand proliferation of particular progenitor cells?
hemopoietic growth factors
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What are the hemopoietic growth factors?
erythropoietin (EPO)
thrombopoietin (TPO)
cytokines
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What does erythropoietin (EPO) do?
increases thenumber of RBC precursors
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where is EPO produced?
primarily by cells in thekidneys that lie between the kidney tubules
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What happens with EPO in renal failure?
EPO release slows and RBC production is inadequate
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What is a hormone produced by the liver that stimulates the formation of platelets from megakaryocytes?
thrombopoietin (TPO)
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What are small glycoproteins that are typically produced by cells such as red bone marrow cells, leukocytes, macrophages, fibroblasts, and endothelial cells?
cytokines
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Generally, what kind of hormones do the cytokins act?
local hormones
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What do cytokines stimulate?
proliferation of progenitor cells in red bone marrow and regulate the activities of cells involved in nonspecific defenses and immune responses
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What are the 2 important families of cytokines that stimulate white blood cells formation?
colony stimulating factors and interleukins
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