Glossary
diaphysis
The diaphysis is the long shaft of a long bone — a tube of compact bone wrapped around a marrow cavity.
The diaphysis is the shaft of a long bone: the straight middle section, built as a tube. Its wall is thick compact bone, which resists bending under load, and its center is the medullary cavity, which holds marrow and fat rather than the weight of solid bone. That hollow shape is the engineering point — a tube resists bending nearly as well as a solid rod at a fraction of the weight, which is what lets a long limb be strong and light enough to swing. The diaphysis meets each end at the epiphysis, and the growth plate of a young bone sits between them, so length is added there while width is added at the periosteum. Long bones do not grow equally at both ends: the femur adds most of its length at the end away from the knee.
Taught in
Related terms
- epiphysis — The epiphysis is the rounded end of a long bone — spongy bone under a thin shell, shaped to meet the joint it forms.
- periosteum — The periosteum is the tough membrane wrapped around a bone's outer surface, carrying its blood vessels and the cells that widen and mend it.
- osteoblast — An osteoblast is the cell that builds bone: it lays down the new matrix and starts the mineral deposit that hardens it.
Source: The anatomy and physiology guide in this course, whose organ and tissue descriptions follow the US National Cancer Institute's SEER Training Modules and MedlinePlus consumer health pages. Both are US federal government material, not subject to copyright in the United States. The definition above is written for this course in our own words. (SEER Training Modules accessed 2026-10-26; definition written 2026-10-27)