Hematopoiesis in the Human Body

During the fetal stage:

• The entire bone marrow is responsible for hematopoiesis.

At the end of the 2nd month of pregnancy:

• The clavicle bone marrow begins to participate in hematopoiesis.

The 3rd month of pregnancy:

• The bone marrow of flat bones (such as the skull, shoulder blade, pelvis) begins to participate in hematopoiesis.

The 4th month of pregnancy:

• The bone marrow of long bones (such as the humerus, femur) begins to participate in hematopoiesis.

Week 11 of pregnancy:

• Bone marrow assumes the function of bone formation.

In adults:

• Hematopoietic marrow is only present in some flat and short bones (such as the skull, shoulder blade, pelvis, vertebrae, sternum).

• Adult bone marrow consists of two types:

• Red marrow: contains immature blood cells and participates in hematopoiesis.

• Yellow marrow: mainly contains fat and does not participate in hematopoiesis.

Hematopoietic and immune organs:

• Primary hematopoietic and immune organs:

• Red bone marrow: produces blood cells and immune cells.

• Thymus: is an important organ in the development and maturation of T lymphocytes.

• Secondary hematopoietic and immune organs:

• Lymph nodes: are the sites where B and T lymphocytes gather, participating in immune responses.