Bone marrow + microscopic structure of compact and spongy bone

What is bone marrow

The soft tissue occupying the medullary cavity of a long bone, the spaces of the spongy bone, and the larger Haversian canals

Two types of bone marrow

Red and yellow

Red bone marrow

Blood cell

What does red bone marrow form?

Hematopoietic tissue

What does red bone marrow consist of?

A delicate mesh reticular tissue saturated with immature red blood cells and scattered adipocytes

In children, what is the medullary cavity filled with

Red bone marrow

What are osteons or Haversian systems

Weight bearing, parallel cylindrical systems along the axis of a compact bone

What does an osteon consist of?

Haversian canal surrounded by concentric layers of calcified bone matrix

Haversian canal

Allow the passage of blood vessels, lymphatic vessels, and nerve fibers

Lamella

Concentric matrix tubes that surround a Haversian canal

This allows the bone to better withstand twisting forces

Collagen fibers in one lamella run one direction, while collagen fibers in adjacent lamellae will run in the opposite direction

Volkmann’s canal

Run perpendicular connecting blood supply in the periosteum to those in the Haversian canals and medullary cavity

Interstitial lamellae

Incomplete lamellae that lie between intact osteons and fill the gaps between them, or are remnants of bone remodeling

Circumferential lamellae

Extend around the circumference of the shaft

Inner circumferential lamellae

Just inside the periosteum

Lacunae

Small cavities where osteocytes occupy at the junctions of the lamellae

Caniliculi

Canals in the lacunae that connect the lacunae to each other and to the central canal

What do the caniliculi allow?

Allow osteocytes to exchange nutrients, waters, and chemical signals to each other via intercellular connections known as gap junctions

Microscopic structure of spongy bone compared to compact bone

Spongy bone appears poorly organized compared to compact bone

What does spongy bone lack?

Osteons

Spongy bone structure

Layers of trabeculae align along positions of stress and exhibit extensive cross bracing, they contain irregularly arranged lamellae and osteocytes interconnected by caniliculi

Why does spongy bone have no Haversian/volkmann canals?

They get their blood supply from red blood cells and red bone marrow