Developmental Changes of RBCs Flashcards
Where is the first site of RBC production in the fetus?
The yolk sac, at 2 weeks of gestation.
Where is the primary site of RBC production in the fetus from gestational week 8 to 5 months?
The liver
Where does RBC production primarily take place after the 5th month of gestation?
The bone marrow.
Describe the changes in location that take place in fetal RBC production.
RBC production starts in the yolk sac (2-8 weeks of gestation), then transitions to the liver (2-5 months of gestation), then transitions to the bone marrow.
Compare the information obtained from mean corpuscular volume (MCV) with that from mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC).
MCV reflects the size of the RBCs, while MCH and MCHC reflect the amount of hemoglobin in RBCs.
Define mean corpuscular hemoglobin (MCH).
The average mass of hemoglobin in each RBC.
Define mean corpuscular hemoglobin concentration (MCHC).
The ratio of hemoglobin mass to the volume of RBCs.
Define RBC distribution width (RDW).
A measure of the variability in RBC size. An increased RDW means that there is increased variation in RBC size.
Define mean corpuscular volume (MCV).
A measure that reflects the size of the RBCs.
How is a reticulocyte count usually reported?
It is often reported as a percentage of reticulocytes in the blood.
What is a reticulocyte?
An immature RBC.
How does the RBC count in a fetus at 12 weeks of gestation compare with the RBC count of an infant at term?
The RBC count triples in that time.
What is the average reticulocyte count for term infants at birth?
~5%
What is the expected MCV of an infant born at term?
Macrocytic, usually ~108 fL
Compare the hemoglobin levels in the capillaries with levels in the venous blood for a newborn? What accounts for the difference?
Hgb levels are much higher in the capillaries than in the venous blood due to a loss of plasma from the capillaries.
What is the expected change in venous hgb, hct, and RBC counts between birth and 3 days of life? What accounts for the change?
All three values will increase between birth and the first 3 days of life due to a postnatal decrease in plasma volume.
What regulates the production of RBCs?
Erythropoietin (EPO)
Where is EPO produced in the fetus? After birth?
Erythropoietin is produced in the liver in the fetus. Production switches from liver to kidney soon after birth.
What regulates the production of erythropoietin?
Tissue oxygenation
What is the average hemoglobin at birth? What causes it?
17 g/dL; this relative polycythemia is due to the low arterial PaO2 in utero that stimulates EPO production and thus increases erythropoiesis.
What factors are responsible for the “physiologic anemia of infancy”?
Arterial PaO2 rises acutely at birth, resulting in a decrease in EPO production. Nucleated RBCs disappear from the peripheral blood and the retic count drops. Red cell lifespan in the first 6-8 weeks of life is around 90 days instead of the usual 120 days. This results in the “physiologic anemia of infancy”, which reaches its nadir around 2 months of age, with an average Hgb of 9-11 g/dL.
What is the average lifespan of a RBC during the first 6-8 weeks of life?
90 days (in contrast to the usual 120 days)
How does the RBC count change postnatally in a preterm infant compared with a term infant?
Both have a drop in Hgb postnatally, but it is a more severe drop in preterm infants, with severity proportional to decreasing birthweight.
What causes anemia to be more severe in preterm compared with term infants?
Preterm infants have inappropriately low levels of EPO and thus cannot stimulate production of RBCs.
When do the average hemoglobin values start to diverge for males and females? Why?
In adolescence, because of the erythroid-stimulating effects of androgens in adolescent males.
Describe the normal changes in MCV from birth through childhood and adolescence.
MCV is usually ~108 at birth (macrocytic), then falls during the first 6-12 months of life, during which time it reaches a nadir of 77 fL. It then rises throughout childhood and adolescence.
What is the typical reticulocyte count after 4 months of age?
< 2%
At what age is it normal to have nucleated RBCs in the peripheral circulation?
In the first week of life.
Describe the basic structure of a hemoglobin molecule.
Hgb is a tetramer made up of 2 pairs of globin chains, each attached to an iron-containing porphyrin ring (heme).
What is the difference between fetal hemoglobin and adult hemoglobin?
Adult hemoglobin contains two pairs of α chains and two pairs of β chains (α2β2). Fetal hemoglobin contains two pairs of α chains and two pairs of γ chains (α2γ2).
Describe the fetal hemoglobin makeup in a 6 month old fetus > term neonate > 4 month old > 12 month old.
6 month old fetus has 90% circulating fetal Hgb > Neonate has 70% > 4 month old has 20% > 12 month old has less than 2% fetal Hgb.
What happens to the oxygen dissociation curve after birth?
After birth the oxygen dissociation curve shifts to the right to allow better release of oxygen to the tissues. (***picture of curve?)
