Spongy and Compact Bone

Two Types of Bone Texture

We take one of your long bones, such as the femurThigh bone; longest and strongest bone in the body; has a large round head and prominent trochanters. By slicing it in a frontalForehead bone; forms the front part of the skull and roof of the orbits. Smooth and curved. section A cut or slice of the body or an organ for study., we separate the anteriorThe front of the body or toward the front when standing in the anatomical position. portion. We separate the posterior portion as well. We would see something like this picture here. The bone is not a complete solid mass. Most of the bone consists of a porous type of bone called spongy boneA porous bone tissue found inside bones, providing lightweight support.. It can withstand twisting, pulling, and pushing from all directions. Spongy bone is supported or surrounded by a denser form of bone tissue called compact boneDense, strong bone tissue forming the outer layer of bones.. 

This compact bone is along only the superficialNear the surface of the body. faces of the bone. It gives the bone strength only in certain directions.  Sometimes this is called a bone collar of compact bone. Like the collar of a shirt, it surrounds the bone. It gives the bone structure and support to maintain its shape. Many of the flat bones in your body are composed of a structure called diploe. Specifically, it refers to spongy bone. This bone is trapped between two layers of compact bone. This is shown in this picture here of the flat bones of the skull. For flat bones this diploe structure creates incredible strength which should be expected from the bones that protect your brain.

Spongy Bone

Your skeleton is comprised mostly of spongy bone Not compact bone tissue. If your skeleton were composed of compact bone, it would weigh too much. Your muscles would not be strong enough to move the bones.  Spongy bones serves to lighten the skeleton while still providing strength and support.  Much like the supports of a bridge spanning a river, spongy bone has structures called trabeculae. These structures are very similar to the trusses that support bridges.

TrabeculaeThe lattice-like structures in spongy bone that support stress distribution. are curving structures of sheets o layers of bone called lamellae or lamella singular.  These trabeculae are found in spongy bone in almost infinite orientations. Spongy bone can take stress from all directions. This capability makes it quite superiorAbove or toward the upper part of the body. to compact bone. Compact bone is only able to withstand force in one, or few, directions. 

Compact Bone

As we just learned layers of bone are called Lamellae or lamella for singular. This becomes confusing because there are many different types of lamellae that create the overall structure of compact bone tissue.  This picture here is similar to a pizza slice of bone. The spongy bone toward the deepAway from the surface of the body. part of the bone. The spongy bone or the interior medullary cavityThe hollow space inside bones that contains bone marrow. would be filled with marrow. The compact bone as you can see is around the superficial face of the bone.

Surrounding the entire bone are lamellae called circumferential. This word relates to the word circumference. The circumference is basically just a measurement of the outline of a circle. As you move from superficial to deep into the bone, you start to encounter these pillars of lamella. They align superior to inferiorBelow or toward the lower part of the body. and are called Osteon. These little pillars give compact bone its incredible ability to withstand gravitational forces. They support the weight of your fleshy tissues.

 Each osteon is surrounded by its own layers of bone called concentric lamellae. In between the osteonsThe structural unit of compact bone, consisting of concentric lamellae around a central canal. and the concentric lamellae are what we call sheets of bone called interstitial lamellaeLayers of bone matrix found between osteons.. I feel like interstitial lamella is just filler. It’s like all the pillars were created and someone said hey don’t forget to fill in the spaces between them.