Where do blood cells originate and initially develop?

Answer 1

this may be a bit elementary, but you should have seen the last answer. i am also not a dr. im just a student and thus this answer will be basic.

first blood cells are made in your bone marrow. they are made from a type of stem cell. this type of stem cell allows a variety of cells to be made based on what the body needs. if it is a red blood cell then first a hormone tells the stem cell it will be a red blood cell, during its development its nucleus is abandoned and it becomes a immature red blood cell or a "reticulocyte". this is then passed into the blood stream and it loses its mitochondria and ribosomes within a day or two. and is a functioning red blood cell.

Answer 2

Haemopoesis is the process of generating formed blood elements.

Formed blood elements (blood cells) are formed in haemopoetic organs

which are these (in order of succession): extraembryonal mesenchyme, intraembryonal mesenchyme, liver, spleen, thymus, bone marrow.

There are 2 periods of haemopoesis:

Prenatal which takes place before birth

Postnatal which takes place after birth

The reason for this is, that while the embryo has no bone marrow to produce

its elements, other haemopoetic tissues have this function assigned.

The prenatal haematopoesis is further divided into three periods

1. Mesoblastic period, during which nuclear blood cells (erythroblasts) are produces from blood islands (formed by mesenchymal cells) first in the extraembryonal mesenchyme(yolk sack, connecting stalk) and later intraembryonal mesenchyme. This period during 2nd month of development of the embryo.

2.Hepatolienal period, starts with infiltration of liver parenchyme with mesenchyme and takes place in the liver(production of erytrocytes, granulocytes, thrombocytes) and spleen (mostly erythrocytes). Note, the erytrocytes no longer have nuclei. Lymphocytes are produced in thymus. This period has its peak during 4th month of development of the fetus. With the ossification of clavicle the

3.Medulolymphatic period begins and gradually becomes the origin of all formed blood elements.

The postnatal haemopoesis is concentrated in haematopoetic red bone marrow (myeloid tissue) and in the tissue of lymphatic organs.

Myeloid tissue of adults is found in the spongy bone of sternum, corpora vertebralia, ribs, clavicula, pelvic bone, flat bones of the skull and proximal epiphyses of long bones e.g. humerus and femur.