17.1 Blood



Quiz 03

The first erythrocytes contain nuclei and derive from stem cells (BFU/CFU-E) that arise in the blood islands of the umbilical vesicle. Centrally lying cells of these blood islands join up thereby into nucleus-containing, large erythroblasts, whereas those peripherally located become endothelial cells. One also calls this extraembryonic phase of the blood formation megaloblastic eryhropoiesis. This extraembryonal erythropoiesis is supplanted by thee embryonic erythropoiesis, which arises in the liver. These stem cells have their origin in the aorto-gonado-mesonephros region. The erythrocytes that arise in the liver are nucleus-free - in contrast to those formed outside the embryo - and are produced there up to the 28th week of pregnancy.


Quiz 04


Quiz 16

A small portion is also formed in the spleen (green in Figure 3). This hepatolienal phase dominates the second trimenon of the pregnancy. In the last trimenon the bone marrow is the most important hematopoietic organ (myeloid phase of the erythropoiesis). Fig. 3 - Proportions of the entire
erythropoiesis in the blood forming

Umbilical vesicle
Bone marrow

Fig. 3
This diagram shows the approximate contributions of the various blood forming organs during pregnancy.

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On the erythrocyte surface membrane there are many blood group attributes, among them the well-known A and B antigenes of the ABO system as well as the rhesus factor.

Overview of the named surface molecules of the erythrocytes (in German).

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Overview of erythropoiesis


Quiz 14

  • Number of erythrocytes per ml blood: ca. 5 millions
  • Diameter of the erythrocytes: 7.5 mm
  • Life expectancy: ca.120 days (at birth ca. 40-70 days)

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