Study Notes for Module 6.3: Long Bones

Long bones transmit forces along the shaft and possess a rich blood supply.
The femur is used as a representative example to examine several aspects of functional anatomy.

The femur can be divided into several key regions, primarily viewed through a frontal (coronal) section.

Long bones consist of:
- Compact Bone: Dense outer layer providing strength.
- Spongy Bone: Also known as trabecular bone; characterized by a porous structure.

Definition: Expanded area at each end of the bone known as epiphysis (e-PIF-i-sis).
Composition: Predominantly spongy bone which has a branching framework.
Function:
- Spongy bone can resist multi-directional forces better than compact bone but is weaker when compressed from a single direction.
- It channels and directs body weight from the proximal epiphysis to the compact bone of the diaphysis.
- Passes forces to the spongy bone of the distal epiphysis, which helps distribute body weight across the articular surface at the knee.

Definition: Also known as the marrow cavity, the medullary cavity is the innermost part (medulla) of the long bone.
Function:
- Serves as a space within the hollow shaft of the bone, does not diminish the strength of the bone.
- The central part of the bone is not exposed to significant compression or tension.
Contents:
- Red Bone Marrow: Highly vascular, involved in blood cell production.
- Yellow Bone Marrow: Composed of adipose tissue; important as an energy reserve.

Definition: Also known as the shaft, it is long and tubular in structure.
Composition:
- The wall of the diaphysis is composed of relatively dense compact bone, providing a sturdy protective layer around the central medullary cavity.

Definition: The metaphysis (me-TAF-i-sis; meta meaning ‘between’) is the narrow zone connecting the epiphysis to the diaphysis.

Compression occurs on the medial side of the shaft and tension on the lateral side.

A. List the major parts of a long bone.
B. Describe the function of the medullary cavity.