GENERAL HISTOLOGY

Detailed explanation-1: -The primitive hematopoietic system is hypothesized to involve a sequential migration of hematopoietic stem cells. They travel from the yolk sac to the liver and later the liver to the bone marrow. The hematopoietic stem cells of adults are in the bone marrow.

Detailed explanation-2: -Hematopoiesis first arises in the extraembryonic yolk sac, and it is generally believed that yolk sac-derived stem cells migrate and seed the fetal liver at approximately week 6 of development in humans.

Detailed explanation-3: -A yolk sac is a structure that develops inside your uterus during early pregnancy. It provides an embryo with nourishment (food). It helps circulate gasses between you and the embryo. The yolk sac also produces cells that turn into important structures, such as the umbilical cord, blood cells and reproductive organs.

Detailed explanation-4: -Embryonic hematopoiesis begins in the yolk sac and changes to definitive hematopoiesis in the fetal liver. The bone marrow becomes the principal site of hematopoiesis late in gestation.