Week 8 Study Guide Blood
Sites of Blood Cell Production and Age-Related Changes
1. Fetal Stage:
- Primary stage: liver
- Additional sites: yolk sac (early weeks), spleen (mid to late fetal life), and bone marrow
(late fetal development)
- Summary: hematopoiesis begins in the yolk sac, shifts to the liver and spleen and finally
transitions to bone marrow before birth.
2. Infancy:
- All bones contain active red marrow capable of producing blood cells.
- Includes both axial skeleton and appendicular skeleton
3. Adulthood:
- Predominant sites: ribs, vertebrae, sternum, and pelvis
- Minor sites: proximal ends of the tibia and humerus
- Change:
- Much of red marrow in long bones is replaced by fatty yellow marrow.
- Extent of active red marrow depends on degree of fatty infiltration.
Key Stages of Erythrocyte Production (Erythropoiesis)
1. Pluripotent Stem Cell (Hematopoietic Stem Cell):
- Location: bone marrow
- Characteristics:
- Nucleated and undifferentiated
- Has potential to give rise to all blood cell types
- Fate: differentiates into myeloid progenitor, becomes committed to erythroid lineage
2. Proerythroblast:
- First recognizable erythroid precursor
- Still nucleated
- Function: begins hemoglobin synthesis
- Appearance: large cell, deeply basophilic cytoplasm due to high RNA content
3. Erythroblast Stages (Basophilic -> Polychromatic -> Orthochromatic)
- Cell becomes progressively smaller and less basophilic as hemoglobin accumulates
- Nucleus condenses and is eventually extruded
- Don’t need the detailed sub-stages, but:
- Hemoglobin content increases
- RNA content decreases
- Basophilia fades to pinkish as hemoglobin dominates
4. Reticulocyte:
- First stage w/o nucleus, but still contains remnants of organelles
, - Short-lived: circulates for 1-2 days before maturing
- Normally: only a small percentage in circulation
- Increased reticulocyte count seen during acute anemia or after blood loss – the bone
marrow releases more immature cells to replace lost RBCs.
5. Mature Erythrocyte (RBC)
- Fully mature, non-nucleated, biconcave disc
- No organelles, maximizes space for hemoglobin
- Function: gas transport
- Lifespan: -120 days in circulation
Fate of Erythrocytes in Blood
1. Lifespan:
- Average lifespan: 120 days
- After this period the erythrocyte membrane becomes less flexible and more fragile.
2. Ongoing Metabolic activity:
- Even though mature erythrocytes lack nucleus and mitochondria, they remain
metabolically active through anaerobic glycolysis.
- Several essential functions:
- (a) Preserve cell membrane integrity, ensuring deformability and preventing premature
lysis
- (b) Maintain hemoglobin structure and iron in its reduced form, which is essential for
oxygen binding.
- (c) Regulate ion transport, particularly sodium and potassium balance, which sustains
osmotic stability.
3. Destruction and Recycling by Macrophages:
- Primary sites: spleen, liver, and bone marrow
- Process:
- Senescent RBCs are phagocytized by macrophages.
- Hemoglobin is broken down into:
- Globin: split into amino acids for reuse
- Heme: converted to bilirubin
- Iron: released and bound to transferrin, which transports it back to the bone marrow for
new hemoglobin synthesis.
4. Self-Destruction in Spleen:
- Spleen acts as a quality control filter
- Old or fragile RBCs cannot squeeze through the narrow splenic trabeculae and sinusoids,
causing them to rupture.
- Remnants are then removed by macrophages within the spleen.
Effects of Exercise Training on Hematocrit
1. Dual Adaptations in Blood Components:
- Exercise training produces two opposing effects on hematocrit:
- Increase RBC production
- Chronic aerobic training stimulates EPO release from the kidneys
- Leads to increased RBC synthesis in bone marrow.
2
Sites of Blood Cell Production and Age-Related Changes
1. Fetal Stage:
- Primary stage: liver
- Additional sites: yolk sac (early weeks), spleen (mid to late fetal life), and bone marrow
(late fetal development)
- Summary: hematopoiesis begins in the yolk sac, shifts to the liver and spleen and finally
transitions to bone marrow before birth.
2. Infancy:
- All bones contain active red marrow capable of producing blood cells.
- Includes both axial skeleton and appendicular skeleton
3. Adulthood:
- Predominant sites: ribs, vertebrae, sternum, and pelvis
- Minor sites: proximal ends of the tibia and humerus
- Change:
- Much of red marrow in long bones is replaced by fatty yellow marrow.
- Extent of active red marrow depends on degree of fatty infiltration.
Key Stages of Erythrocyte Production (Erythropoiesis)
1. Pluripotent Stem Cell (Hematopoietic Stem Cell):
- Location: bone marrow
- Characteristics:
- Nucleated and undifferentiated
- Has potential to give rise to all blood cell types
- Fate: differentiates into myeloid progenitor, becomes committed to erythroid lineage
2. Proerythroblast:
- First recognizable erythroid precursor
- Still nucleated
- Function: begins hemoglobin synthesis
- Appearance: large cell, deeply basophilic cytoplasm due to high RNA content
3. Erythroblast Stages (Basophilic -> Polychromatic -> Orthochromatic)
- Cell becomes progressively smaller and less basophilic as hemoglobin accumulates
- Nucleus condenses and is eventually extruded
- Don’t need the detailed sub-stages, but:
- Hemoglobin content increases
- RNA content decreases
- Basophilia fades to pinkish as hemoglobin dominates
4. Reticulocyte:
- First stage w/o nucleus, but still contains remnants of organelles
, - Short-lived: circulates for 1-2 days before maturing
- Normally: only a small percentage in circulation
- Increased reticulocyte count seen during acute anemia or after blood loss – the bone
marrow releases more immature cells to replace lost RBCs.
5. Mature Erythrocyte (RBC)
- Fully mature, non-nucleated, biconcave disc
- No organelles, maximizes space for hemoglobin
- Function: gas transport
- Lifespan: -120 days in circulation
Fate of Erythrocytes in Blood
1. Lifespan:
- Average lifespan: 120 days
- After this period the erythrocyte membrane becomes less flexible and more fragile.
2. Ongoing Metabolic activity:
- Even though mature erythrocytes lack nucleus and mitochondria, they remain
metabolically active through anaerobic glycolysis.
- Several essential functions:
- (a) Preserve cell membrane integrity, ensuring deformability and preventing premature
lysis
- (b) Maintain hemoglobin structure and iron in its reduced form, which is essential for
oxygen binding.
- (c) Regulate ion transport, particularly sodium and potassium balance, which sustains
osmotic stability.
3. Destruction and Recycling by Macrophages:
- Primary sites: spleen, liver, and bone marrow
- Process:
- Senescent RBCs are phagocytized by macrophages.
- Hemoglobin is broken down into:
- Globin: split into amino acids for reuse
- Heme: converted to bilirubin
- Iron: released and bound to transferrin, which transports it back to the bone marrow for
new hemoglobin synthesis.
4. Self-Destruction in Spleen:
- Spleen acts as a quality control filter
- Old or fragile RBCs cannot squeeze through the narrow splenic trabeculae and sinusoids,
causing them to rupture.
- Remnants are then removed by macrophages within the spleen.
Effects of Exercise Training on Hematocrit
1. Dual Adaptations in Blood Components:
- Exercise training produces two opposing effects on hematocrit:
- Increase RBC production
- Chronic aerobic training stimulates EPO release from the kidneys
- Leads to increased RBC synthesis in bone marrow.
2
