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Wize University Physiology Textbook > Blood

Erythropoiesis

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Erythropoiesis

Erythropoiesis is the production of new red blood cells.
  • This occurs in the bone marrow
  • It is stimulated by a hormone called erythropoietin (EPO)
  • EPO is produced by the kidney in response to low oxygen in the blood

  • Reticulocytes are immature RBCs
  • The number of them is a sign of how hard the bone marrow is working to produce new RBCs
  • Normal levels are ~1% of RBCs

  • Men have higher hematocrit % than women
  • Hematocrit is the percentage of blood occupied by RBCs
  • Testosterone stimulates release of erythropoietin AND increases how sensitive to it the pre-RBCs are
  • Estrogen has the opposite effects
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Factors Affecting Red Blood Cell Production

RBC production will be stimulated by EPO anytime there's low oxygen levels (hypoxia). Therefore, this can be caused by many different issues:
  1. High altitude
  2. Lower partial pressure of oxygen
  3. Excessive bleeding (hemorrhage)
  4. Loss of hemoglobin/RBCs decreases the oxygen-carrying capacity of blood
  5. Anemia
  6. Means reduced ability of blood to carry O2 compared to normal
  7. There are many types and causes
  8. Lung issues
  9. RBCs cannot oxygenate well
  10. Increased exercise


Red Blood Cell Destruction

  • RBCs have a lifespan of ~120 days
  • When they are old, macrophages eat them up (phagocytosis), digest and destroy them
  • The heme portion of hemoglobin in RBCs is converted to a compound called BILIRUBIN
  • This bilirubin normally goes to the liver, which ultimately dumps it into the intestine

What happens to the iron?
  • The iron in heme gets recycled
  • It is transported in blood to the bone marrow by transferrin
  • It can also be stored in organs (liver, spleen, gut) bound to ferritin
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Jaundice

Also called icterus, is the name given to the yellow-ish discoloration of skin and sclera (white part of the eye) due to increased levels of bilirubin in the blood.


The causes of jaundice can be various:

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An endurance athlete has been training for an upcoming marathon. How is their body reacting to the increased exercise, particularly with regards to red blood cell production?

Exercise causes increased oxygen consumption in tissues. This is why there's an increase in heart rate while exercising, in order to pump blood faster to organs demanding oxygen. Strenuous exercise, in which there's high tissue demand of O2, causes lower blood levels of available oxygen (hypoxia) which is sensed by the kidneys.

The kidneys produce erythropoietin -> circulates to the bone marrow -> stimulates proliferation of erythrocyte progenitor cells AND their differentiation into mature RBCs.

Regarding erythropoiesis:
Which of the following will not result in increased RBC production?
Regarding RBC destruction, select the correct statements: