The canal found in the center of the concentric rings in bone is called the Haversian canal, also known as the central canal or osteonic canal. It sits at the core of a structure called an osteon, which is the basic building block of compact (dense) bone tissue. Each osteon looks like a tiny cylinder made of rings stacked around a central tunnel, and that tunnel is the Haversian canal.
What the Haversian Canal Contains
The Haversian canal isn’t hollow. It carries blood vessels, lymphatic vessels, and nerves through the dense bone tissue. These blood vessels are the lifeline for surrounding bone cells, delivering oxygen and nutrients while removing waste. Without this canal running through the center, the tightly packed bone matrix would have no way to keep its cells alive.
How the Rings Are Organized
The rings surrounding the Haversian canal are called lamellae. These are concentric layers of bone matrix, mostly made of collagen fibers and minerals, arranged like the growth rings of a tree trunk. Between these rings, bone cells called osteocytes sit in small pockets known as lacunae.
These osteocytes aren’t trapped in isolation, though. Tiny channels called canaliculi branch outward from the Haversian canal, threading between the lamellae to reach each lacuna. The osteocytes extend long, finger-like projections through these channels, connecting to neighboring osteocytes through gap junctions. This creates a communication and nutrient-sharing network that links every bone cell in the osteon back to the blood supply in the central canal.
Think of it like a wheel: the Haversian canal is the hub, the canaliculi are the spokes, and the osteocytes in their lacunae are stations along those spokes, passing nutrients and chemical signals from cell to cell.
How Osteons Connect to Each Other
Each osteon is a self-contained unit, but bone needs a way to link them together. That job falls to Volkmann’s canals, which run perpendicular to the Haversian canals. These horizontal passages carry blood vessels that arise from the outer and inner bone surfaces and connect with the vessels inside each Haversian canal. The result is an interconnected vascular network running both vertically and horizontally through compact bone, ensuring blood flow reaches every osteon.
Why the Canal Matters for Bone Health
The size and density of Haversian canals change over a lifetime. As people age, or in conditions like osteoporosis, the proportion of compact bone occupied by pore spaces (including the canals) increases. This is called cortical porosity, and it’s one of the key indicators of weaker, more fragile bone. Elevated cortical porosity is particularly common after menopause. Essentially, the canals and surrounding spaces widen while the dense bone matrix between them thins, reducing the bone’s overall strength.
This is why the Haversian canal is more than just an anatomy exam answer. It represents the balance compact bone maintains between being dense enough to bear weight and porous enough to stay nourished. When that balance tips too far toward porosity, fracture risk rises.