Bone marrow is another important function of the skeletal and circulatory system.

The production of red blood cells (RBCs) and white blood cells (WBCs) are essential.

Marrow is found within certain bones.

It is a tissue in the center of the bone or also referred to as the “hollow” area of the bone.

There are two types of bone marrow:

1.)  Red Marrow
2.)  Yellow Marrow

At birth – all bone marrow is red marrow only, but, as age increases there is larger amount of yellow marrow that is formed.

In an adult there is about a 50-50 finding of yellow marrow compared to red marrow.


This marrow contains mostly Myeloid tissue

Myeloid tissue can also be found in the spleen and liver

This tissue allows for the body to perform hematopoiesis.

bonemadeHematopoiesis is the production or formation of blood cellular components

The cellular components are necessary and all begin from a “stem cell

This cell is unique in that it can mature into several different cell types.

The following are results of hematopoiesis

1.)   Erythrocyte
2.)  Thrombocytes
3.)  Basophil
4.)  Neutrophil
5.)  Eosinophil
6.)  Macrophage
7.)  Plasma cell
8.)  Lymphocyte

The following bones are typically Red marrow:

-  Skull
-  Vertebrae
-  shoulder
-  hip bone
-  ribs
-  femur           *(yellow is also found)
-  humerus       *(yellow is also found)



Stroma is found mostly in yellow marrow.

Hematopoiesis isn’t directly involved with stroma

Cells that constitute yellow

1.)  Fibroblasts
-  this cell type synthesis extracellular matrix and collagen
       -  play a role in wound healing
-  play a role in maintaining structure

2.)  Macrophages
-  are white blood cells
-  attack and defend the body

3.)  Adipocytes
-  are fat cells
-  help store energy
-  2 types:  white and brown

4.)  Osteoblasts
       -  is responsible for the formation of bone
-  Produce osteoid
-  help reshape bone

5.)  Osteoclasts
-  cause bone breakdown or “resorption”

6.)  Endothelial cells
       -  forms the sinusoids


Bone Marrow Barrier

This is a barrier that doesn’t allow small blood cells [non-mature]
from leaving the bone marrow.

Transplant of bone marrow

It is possible to take bone marrow from one person and place it into the bone of another.

Transplants are done in cases of diseases of bone marrow

Some drugs such as chemotherapy drugs or radiation can also destroy bone marrow.

Sometime prior to such therapy bone marrow is “harvested” to be later place back
in the person of which the damage will occur.

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