Question

In human embryo , main hemopoietic tissue is
A) Spleen
B) Liver
C) Bone marrow
D) Kidney

Answer 1

Hint:The tissue that gives rise to blood cells during the hematopoiesis process.In comparison to most other organs, the hematopoietic system is one of the first complex tissues to develop in the incipient embryo, and different cell types originate from some distinct anatomical niches that alter temporally and spatially until the bone marrow and thymus gradually stabilise.

Complete answer:
The hematopoietic tissue is the bone marrow, lymph nodes, yolk sac, liver, spleen, and thymus of the embryo and foetal stage of vertebrates, but hematopoiesis occurs in the red bone marrow after birth (see myeloid tissue). The numerous forms of stem cells that give rise to erythrocytes and leukocytes in hematopoietic tissue are all originally derived from hematopoietic stem cells (or hemocytoblasts).

Hematopoiesis is essentially the mechanism by which blood cells are produced by the body. It starts early in an embryo's development, well before birth and continues for an individual's life. Often referred to as primitive hematopoiesis, hematopoiesis produces only red blood cells in the embryo that can provide oxygen to the developing organs. The yolk sac, which nourishes the embryo before the placenta is fully developed, regulates hematopoiesis at this stage of development.

The hematopoiesis phase travels to the liver, spleen, and bone marrow as the embryo continues to develop, and starts producing other forms of blood cells.A type of white blood cell called lymphocytes is produced by the lymph system, especially the spleen, lymph nodes, and thymus. Another type of white blood cells called monocytes, are formed by tissue in the liver, spleen, lymph nodes and some other organs.

In mammals, during a significant duration of prenatal ontogenesis, the liver acts as the primary hematopoietic organ. In a complex microenvironment that regulates their proliferation and differentiation, haematopoietic cells of the foetal liver exist.

Various cell populations, including epitheliocytes, macrophages, different stromal elements (hepatic stellate cells, fibroblasts, myofibroblasts, vascular smooth muscle and endothelial cells, mesenchymal stromal cells), as well as cells undergoing epithelial-to-mesenchymal transition, create this microenvironment.

Thus the correct answer is option (B) i.e, Liver.

Note:During the first weeks of embryonic development, hematopoiesis starts. From a stem cell that can grow into any other cell, both blood cells and plasma develop. In humans, hematopoiesis begins in the yolk sac and transitions into the liver temporarily.