Long Bone Anatomy and Compact Bone Structure: Key Terms

Epiphysis

The enlarged end of a long bone, made mostly of spongy bone.

Proximal epiphysis

The end of a long bone closest to the body's midline or point of attachment.

Distal epiphysis

The end of a long bone farthest from the body's midline or point of attachment.

Diaphysis

The shaft of a long bone, made mostly of compact bone.

Spongy bone

Lightweight, porous bone found mainly in the epiphyses; contains red bone marrow.

Trabeculae

Thin bony plates that form the network of spongy bone.

Epiphyseal line

The remnant of the growth plate after bone growth is complete.

Epiphyseal plate

A cartilage growth plate that allows long bones to increase in length.

Articular cartilage

Smooth hyaline cartilage covering bone ends at joints; reduces friction and absorbs shock.

Periosteum

Tough connective tissue covering the outer bone except at joint surfaces; helps growth and repair.

Compact bone

Dense, hard outer bone that provides strength, support, and protection.

Medullary cavity

Hollow space inside the diaphysis that contains yellow bone marrow.

Yellow bone marrow

Fat-storing marrow mainly found in the medullary cavity.

Red bone marrow

Marrow that produces blood cells, found in spaces within spongy bone.

Endosteum

Thin membrane lining the medullary cavity and surfaces of trabeculae.

Osteoblast

A bone-forming cell that builds new bone tissue.

Osteoclast

A bone-resorbing cell that breaks down bone tissue.

Osteocyte

A mature bone cell found in a lacuna that maintains bone tissue.

Osteon

The cylindrical structural unit of compact bone, made of concentric lamellae.

Lamella

A layer or ring of calcified bone matrix surrounding a central canal.

Haversian canal

The central canal of an osteon containing blood vessels and nerves.

Volkmann's canal

A transverse canal connecting Haversian canals and carrying blood vessels and nerves.

Lacuna

A small cavity in bone matrix that houses an osteocyte.

Canaliculi

Tiny channels connecting lacunae and allowing nutrient and waste exchange.

What is the shaft of a long bone called?

Diaphysis.

Where is spongy bone located in a long bone?

Mainly in the epiphyses.

Where is yellow bone marrow located?

Medullary cavity.

Where is red bone marrow found?

In spaces within spongy bone.

What covers the outer surface of a bone?

Periosteum, except where articular cartilage covers joints.

What forms the dense outer layer of bone?

Compact (cortical) bone.

What cushions the ends of bones at joints?

Articular cartilage.

What lines the medullary cavity?

Endosteum.

Where are blood cells produced?

Red bone marrow.

What does an osteoblast do?

Builds new bone tissue.

What are the concentric rings of bone matrix called?

Lamellae.

What is the central canal of an osteon called?

Haversian canal.

What connects Haversian canals?

Volkmann's canals.

Why are canaliculi important for osteocytes?

They allow exchange of nutrients, wastes, and signals.

How do compact bone and spongy bone differ in location?

Compact bone forms the dense outer layer; spongy bone is inside, especially at bone ends.

What helps bones resist bending and compression?

Compact bone organized into osteons.

What is another name for spongy bone?

Cancellous bone.

What is another name for compact bone?

Cortical bone.

What happens to the growth plate when growth ends?

Its cartilage is replaced by bone, leaving the epiphyseal line.

Why does the medullary cavity reduce bone weight?

Its hollow structure makes the bone lighter.

What do osteocytes do?

Maintain bone matrix and communicate with neighboring cells.