Question

Describe the microscopic features of osseous tissue that help long bones withstand stress without breaking

Answer 1

A lateral stress placed on a bone actually causes compression of the bone on the side of impact and stretching (tearing) on the side opposite of the impact.

Mid-way through the bone, these "compressive" and "tearing" forces cancel each other out, and thus tough, compact bone is not needed in the middle. Instead, this middle area (or "medullary cavity") is filled with yellow and red bone marrow.

The outer rim (or "bony collar") is what experiences the greatest stress on lateral impact. It withstands this stress in the following ways:

On the side of impact, the bony collar withstands compressive crushing by virtue of the tough hydroxyapatite crystals in its extracellular matrix. Arranged in concentric layers within the osteons of compact bone, these hydroxyapatite crystals serve as weight-bearing pillars for the bone.

On the side opposite of the impact, the bony collar withstands tearing apart by virtue of the vertically arranged bundles of tough collagen in the extracellular matrix of bone. This collagen is oriented in a spiraling vertical pattern in which the fibers in each concentric lamella are roughly perpendicular to those in adjacent lamellae.