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Bone  Marrow

Bone marrow is the area within certain bones, a spongy tissue, that acts to help produce certain blood cells. It is an important function of the Skeletal and Circulatory systems.

The production of red blood cells (RBCs) and white blood cells (WBCs), and more occur in this area. The bone marrow often contains stem cells which help in the production of new cells.

Over 500 billion blood cells per day are produced. Bone marrow in humans is often located in the ribs, vertebrae, sternum, and bones of the pelvis.

The tissue at the center of the bone can also be referred to as the “hollow” area of the bone.

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 a 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.

Red

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.

Hematopoiesis 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 the 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)

Yellow

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 the 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 a 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 the bone marrow.

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