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hematopoiesis
blood cell formation
where does hematopoiesis occur
occurs in red bone marrow of skull, pelvis, ribs, sternum, and epiphysis of long bones
where is red bone marrow found
in spongey bone
where do blood cells come from
all blood cells are derived from a common stem cell called hemocytoblasts
what does hemocytoblast differentiation lead to
the formation of all other formed elements in a series of steps
what are erythrocytes unable to do
divide, grow, or synthesize proteins as adult cells
how long does it take for erythrocytes to wear out
100-120 days
what happens when erythrocytes are worn out
red blood cells are eliminated by phagocytes in the spleen or liver
how are lost erythrocytes replaced
by a division of hemocytoblasts in the red bone marrow
how is the rate of hemocytoblasts being created controlled
a hormone called erythropoietin
why do kidneys produce erythropoietin
as a response to reduced oxygen levels in the blood
how is homeostasis maintained
by a negative feedback loop from blood oxygen levels
negative feedback
a stimulus is released by the action of an effector
first step in negative feedback
the stimulus occurs due to a decreased red blood cell count, decreased availability of oxygen to blood, or increased tissue demands for oxygen
second step in negative feedback
there are reduced oxygen levels in blood
third step in negative feedback
the kidneys release erythropoietin
fourth step in negative feedback
erythropoietin stimulates red blood cell production in the red bone marrow
fifth step in negative feedback
there is an enhanced amount of erythropoietin
sixth step in negative feedback
there are more red blood cells
seventh step in negative feedback
there is an increased mount of oxygen, so carrying ability of blood increases
how does the number of RBC decrease
donate blood or blood cells wear out
what causes an increased tissue demands for oxygen
exercise
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