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The composition of blood
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Includes descriptions of the site of hematopoiesis, growth factors involved, structure and synthesis of hemoglobin and red blood cell destruction
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Composition of the BloodMonday, 20 September 2021 5:02 PM
Site of hematopoiesis
- Fetus
o 0-2 months - yolk sac
o 2-5 months - liver / spleen
o 5-9 months - bone marrow
- Infants
o Actively producing blood cells in bone marrow
§ Almost all bones
- Adults
o Fewer bones produce
o Vertebrae / ribs / sternum / skulls / sacrum / pelvis / proximal ends of femur
- Pluripotent hematopoietic stem cell
o Can almost give rise to all blood cells
§ Differentiates into
• Lymphoid stem cell
o Lymphocytes
• Myeloid stem cell
o Blood transfusion
§ Transfusion of hematopoietic stem cells
§ From donor to patient
§ Regenerate all the normal blood cells in recipient
§ It must be in the right environment and under the influence of certain growth
factors
- Growth factors
o Erythropoietin - EPO
§ Increases the formation of red blood cells
o Thrombopoietin
§ Increases the formation of platelets
o Granulocyte colony stimulating factor
§ Increases granulocytes (basophils / neutrophils / eosinophils )
o Monocyte colony stimulating factor
§ Increases monocytes (macrophages)
o Granulocyte monocyte colony stimulating factor
§ Increases both granulocytes and monocytes
Regulation of erythropoiesis
- Key hormone – EPO
- Androgen and thyroxine also play a role in production of red blood cells
o Androgen
§ Enable males to have a higher red blood cell count
, Regulation of erythropoiesis
- Key hormone – EPO
- Androgen and thyroxine also play a role in production of red blood cells
o Androgen
§ Enable males to have a higher red blood cell count
o Thyroxine
§ Abnormalities in thyroxine can cause anemia or other issues
- Nutrients like iron, vitamin B12, and folate
o In anemia when hemoglobin concentration is low, could be due to deficiency of the
above nutrients
o Important for the formation of red blood cells and hemoglobin
- EPO regulated by negative feedback of circulating red blood cells
o A decrease in O2 delivery to kidney
o Kidneys sense that oxygen carrying capacity of the blood is low
o Increase EPO secretion
o Increase plasma EPO
o Increase production of erythrocytes in bone marrow
o Increase blood hemoglobin concentration and thus the blood O2 carrying capacity
o Restore O2 delivery to normal
- Each red blood cell contains 640 million hemoglobin
- Interaction in bone marrow with hemopoietic stem cells with other cells
o Determines the differentiation of the stem cell
Hemoglobin
- 4 globin chains with 1 haem each
- 2 parts to each subunit
o Haem
§ Contains protoporphyrin ring
• Combines with an iron
o Forms the haem group
§ One haem binds to one globin chain to form one molecule of hemoglobin
o Globin
- 3 types of hemoglobin
o A
§ Found in adults
§ 2 Alpha chains and 2 beta chains
o A2
§ Sub-form of A
§ 2 alpha chains, 2 delta chains
§ Higher affinity for oxygen
o F
§ Fetus
§ 2 alpha chains and 2 gamma chains
§ predominant form of hemoglobin in the fetus
§ mother carries the oxygen in haemoglobin A
• reaches placenta where there is hemoglobin F
• F has a stronger power to bind to Oxygen then A
o Facilitates the diffusion of oxygen from A to F across the
placenta to the fetus
§ After birth, the baby can’t depend on mother
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