A&P 1 - Unit 2 - The Skeletal System - Microscopic Structure of Bones

ž Bone Cell Types ž Microscopic Histology of Compact Bone

ž The structural unit of compact bone is called the OSTEON. ž Each OSTEON consists of the hard bone matrix arranged in concentric rings (CONCENTRIC LAMELLAE) around a single central canal.

ž Interstitial lamellae are between osteons and are the remnants of older osteons that have been partially destroyed during bone replacement, an ongoing process. ¡ Interstitial lamellae contain osteocytes living in lacunae. ¡ Canaliculi are also present. ž Circumferential lamellae are lamellae on the outer surface of bone – directly under the periosteum and running in the direction of the circumference of the bone.

ž The Central Canal is oriented along the long axis of the bone ž The Central Canal contains blood vessels (Haversian vessels) that carry nutrients and oxygen to and waste products away from the bone cells (osteocytes) in the lacunae. ž Remember, mature bone cells, called OSTEOCYTES, live in the small spaces in the lamellae called LACUNAE. ž Each lacuna is fluid-filled. Lacuna means “Little Lake.”

ž Tiny canals, called CANALICULI, connect the cellular processes of the osteocytes to each other and to the Haversian blood vessels.

ž So, how does blood get from the outside of the bone to the Haversian vessels? ž PERFORATING VESSELS run within canals (Volkmann’s Canals) that run at right angles to the Central canals, connecting the vessels of the periosteum to the Haversian blood vessels that run within the central canal of each ostreon!

Compact vs Spongy Bone

If one were to compare spongy and compact bone, one might compare: (the answer to your essay question should include at least 7 of the following) ž Location ž Relative density ž Presence of Osteocytes ž Lacunae ž Canaliculi ž Trabeculae ž Osteons ž Lamellae ž Concentric lamellae ž Interstitial lamellae ž Red marrow and Location ž Yellow marrow and Location

Compact Bone - Architecture of the Osteon

ž Blood vessel of the periosteum ž to the perforating blood vessel in a Volkmann’s Canal ž to Haversian Blood Vessel in the Central Canal (Haversian Canal) ž to canaliculi ž to osteocyte in a lacuna

ž Perforating Blood Vessel. (Travels through the Volkmann’s Canal across to the Central Canal) ž To the Haversian Blood Vessel. (Runs through the center of the Central Canal of the osteon) ž To the Canaliculi. (“Little Canal”). (Nutrients, oxygen, ammonia, and CO2 diffuse from the Haversian Blood Vessel into the canaliculi.

— In the ends of long bones — Above and below the epiphyseal plate (before bone elongation stops) — Above and below the epiphyseal line (after elongation stops) — fills most irregular bones (bones of the skull, vertebrae and hips)

— On the following slide: — Notice the trabeculae of spongy bone in the head of the bone. — The arrangement of the osteoid changes as we enter the diaphysis of the bone

Ends of Long Bones

Bones of the Skull