Blood Vessels and Marrow inside Bones

Most of us know that new blood cells are generated in bone marrow, the innermost part of bones, but still most of us don't know that bones have also got blood vessels inside them. Recently some researchers have found new blood vessels inside bones and found that bones also have closed bloodstream, just like other organs. 

Earlier theories described that there is a single arterial canal and two venous canal in bones, but now researchers have found thousands of blood vessels inside bones. It is surprising that we are still discovering new anatomical structures in human body, which are not yet described in any textbook. The newly discovered variety of blood vessels go straight from outer region of bone to the inner spongy region and small capillaries cover the whole bone.

Blood vessels inside bones provide oxygen and nutrients to bones from our diet, and carry out new blood cells into our body. These new blood cells also contain white-blood-cells which are an important part of our immune system.

Our bones are very hard organs, which made some earlier biologists consider it made up dead tissues. Later we found that there are nerves, blood vessels and pain receptors. That is why a bone-fracture cause bleeding and lots of pain.

Our immune system also utilizes the power of these blood vessels as an underground train system which helps in sending white blood cells to the infection site through the fastest possible route. If we have got an infection in leg then immune cells are generated in leg (not in the arm), to deliver it to infection site as fast as possible.

Commonly known bone marrow inside bones is not as simple as it seems. It not just creates blood cells but a lot of other things as well. There are two types of bone marrow : red and yellow. Children have more Red Bone Marrow, while Red one changes into yellow one as we grow adult. In adults red bone marrow is found in only a few major bones like skull, ribs, spinal cord, pelvis, thigh bone, shin bone and upper arm bone. In adults other bones mostly contain just yellow bone marrow. 

Red bone marrow generates blood stem cells, which can later grow into red blood cells, white blood cells and platelets. Thus red bone marrow becomes a factory of blood and immunity in our body. It also breaks down old RBC (Red blood cells), which is a task mostly done by liver and spleen. 

Yellow bone marrow contains mesenchymal stem cells that can grow into bones, fats, muscles or cartilage. Thus this bone marrow helps in repair of bones and muscles, and also helps in making energy reservoirs in the form of fat.

Some researchers have found that as we grow old the yellow bone marrow starts to transform itself into bone. It might be a reason why we grow old with ageing. 

Reference:

• https://www.sciencedaily.com/releases/2019/01/190130103812.htm
• https://www.healthline.com/health/function-of-bone-marrow