Haversian System: Understand the Structure, Explain the Function, Apply Your Knowledge

 HAVERSIAN SYSTEM

Definition:

The Haversian system (osteon) is the structural and functional unit of compact bone but absent in spongy bone.

Structure:

1. Haversian canal: A central canal containing blood vessels (artery & vein) and nerves.
2. Concentric lamellae: they are rings shape calcified bone matrix arranged around the Haversian canal.
3. Lacunae: Small depressed spaces between the lamellae containing osteocytes.
4. Canaliculi: Tiny channels within lamellae connecting lacunae with one another and with the Haversian canal.
5. Cement line: The outer boundary of the Haversian system.
6. It contain Volkmann’s canal.                                                                                                                 

   

   Haversian system 

   
   

Volkmann’s Canal

Definition:

Volkmann’s canals are transverse or oblique channels in compact bone (they are absent in spongy bone) that connect adjacent Haversian canals with one another and convey blood vessels from the periosteum and medullary cavity.

Contents:

1. Blood vessels
2. Nerve fibres

Important features:

• They run transversely or obliquely to the Haversian canals.
• They are lined by endosteum, the lining of medullary cavity.
• They do not have concentric lamellae surrounding them like Haversian canal.

 

Functions:

·         They connect Haversian canals with one another and with blood vessels from the periosteal and medullary regions.

• They are connected with canaliculi, so they help to supply nutrients and oxygen to osteocytes.
• Provides strength and support to compact bone.
• Facilitates the removal of metabolic waste from osteocytes.

Important point: Nutrients diffuse from blood vessels in the Haversian canal through the canaliculi to reach osteocytes located far from the blood supply.

Blood Supply of Haversian

Haversian canal (HC): Blood vessels are derived mainly from

1.       Nutrient artery

2.      periosteal arteries

3.       Metaphyseal arteries

4.      Epiphyseal arteries

 

UNDERSTANDING QUESTIONS FROM THE HAVERSIAN SYSTEM

Question:

Why is the Haversian system structurally adapted for the passage of nutrients to osteocytes located far away from the Haversian canal?

Answer:

The Haversian system contains a central Haversian canal carrying blood vessels. Lacunae are small spaces that contain osteocytes.

Canaliculi connect the lacunae with one another and with the central canal.

Haversian canal → Canaliculi → Lacunae → Canaliculi → Lacunae

Thus, nutrients and oxygen reach nearby osteocytes through the canaliculi. In the same way, nutrients and oxygen pass through the canaliculi from one lacuna to another, allowing distant osteocytes to receive nutrients and oxygen.

Question:

Why is the Haversian system present in compact bone but not in spongy bone?

Answer:

Compact bone has a dense matrix, so vascular canals and canaliculi help supply its osteocytes.

Spongy bone has thin trabeculae exposed to marrow spaces, so osteocytes receive nutrients from the blood vessels in the bone marrow by diffusion through the canaliculi, without requiring a Haversian canal.