Blood islands

Blood islands are the earliest form of hematopoiesis, the process by which the body produces blood cells. They are clusters of developing blood cells and blood vessels found in the yolk sac of the mammalian embryo.

Formation

Blood islands form in the yolk sac during the third week of embryonic development. They are composed of a central mass of hematopoietic (blood-forming) cells, surrounded by a ring of angioblasts, which are cells that will develop into endothelium, the tissue that lines blood vessels.

Development

As development progresses, the angioblasts differentiate into a simple squamous epithelium, which forms the walls of the blood vessels. The hematopoietic cells in the center of the blood island differentiate into primitive erythroblasts, which are immature red blood cells. These cells begin to produce hemoglobin, the protein that carries oxygen in the blood.

Function

Blood islands are the primary site of blood formation in the early embryo. They give rise to both the blood cells and the blood vessels, and thus play a crucial role in establishing the circulatory system.

Clinical significance

Abnormalities in the formation or function of blood islands can lead to a variety of congenital disorders, including certain types of anemia and leukemia. Research into the development and function of blood islands may lead to new treatments for these and other blood-related disorders.

See also

• Hematopoiesis
• Yolk sac
• Embryonic development
• Angiogenesis