Bone Macro-anatomy

Long Bone Anatomy

Before we get started here it’s important to note that this is a mini lecture pertaining to a chapter quiz. This is not bone identification that is based on memorization of bone features. Don’t be confused. We’re using a humorous example here to help us learn some of these terms.

Each end of the bone is called an epiphysisThe expanded ends of a long bone.. There is a distal epiphysis and a proximalCloser to the point of attachment or origin. epiphysis. This is why we had to learn those two terms in a previous mini lecture. Between the two epiphyses is the shaft of the bone which is more officially called the diaphysisThe shaft of a long bone.. Bones have their own connective covering separating them from the overlying tissue which is usually muscle. These superficialNear the surface of the body. covering is called the periosteum. This wrapping will be discussed in more detail but actually consists of its own 2 layers. Deep to the periosteum is a structure known as the bone collar. It entirely surrounds the bone but is just a superficial covering. It takes its name from the collar of a shirt which surrounds the neckNarrow region just below the head; common fracture site.. If we move more internally or deeper into the bone, we encounter spongy boneA porous bone tissue found inside bones, providing lightweight support.. Then, we find a marrow cavity that can contain red or yellow marrow. Think about these structures and now a scalpel would encounter them if cutting into a bone.

Vascularization

Bones bleed and bones hurt when you break them. This is because bones are both innervated and vascularizedTo invade a tissue with blood capillaries.. As the bone is forming, blood vessels perforate the bone. They enter it at an angle that is perpendicular to the periosteum. Little tiny holes in every bone, called nutrient foramina, are meant for arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr, veinsBlood vessels that return deoxygenated blood to the heart (except pulmonary veins, which carry oxyge, and nerves to perforate the bone. These perforating canals branch off into central canalsA hollow canal in an osteon containing blood vessels and nerves. that run parallel to the periosteum and the color of the bone. These general ideas apply to flat bones too. They have perforating canals. Also, their canals run in a different direction. This type of vascularization creates a network of blood vessels. These vessels penetrate deeply into the bone. They diffuse nutrients like glucoseA simple sugar that is the main source of energy for cells. and oxygen. Vascularization allows your bones to heal after being broken.

Periosteum

The periosteum is the most superficial wrapping that isolates the bone from any surrounding tissue. Which is usually skinThe body’s largest organ, providing protection and regulation. or muscle. The periosteum is like other superficial organ wrappings. It provides entry paths for blood vessels and nerves into the organ deeper than the wrapping. The periosteum of bone has a special job functioning in growthAn increase in size and number of cells. and repair in addition to these other jobs. The periosteum has two layers to it. The outer fibrous layer separates the bone from other tissues. It is composed of a dense regular or dense irregular type tissue. There is an inner layer to the periosteum but this layer is formed of osteoblasts the cellsThe basic structural and functional units of life. that create bone.

Bone Wrappings

The endosteumA thin connective tissue lining the marrow cavity. is an incomplete layer of cells that line the marrow cavity. I think of the endosteum more like fishnet stockings and tights because it’s an incomplete layer. Osteogenic cellsStem cells that develop into osteoblasts. are stem cells that are capable of dividing into other types of bone cells like osteocytes and osteoblasts. When a bone grows, these osteogenic cells create the correct balance of osteoblasts and osteoclasts. Hormones usually direct this process to maintain that growth. There is another mini lecture. It talks about bone remodeling. This process occurs throughout your lifetime. It also utilizes the cells derived from these osteogenic cells.

Medullary Cavity

In long bones, such as the femurThigh bone; longest and strongest bone in the body; has a large round head and prominent trochanters, ribsCurved bones forming the rib cage; articulate with thoracic vertebrae and most with the sternum., or even the metacarpalsPalm bones numbered thumb (1) to pinky (5); heads form knuckles. and metatarsalsLong bones of the foot; numbered big toe (1) to pinky toe (5)., there is an internal medullary cavityThe hollow space inside bones that contains bone marrow.. This cavity is sometimes called the marrow cavity.