Dr. Cohn BIOL 319 Lecture Exam 3 - Outline 6 & 7

This set covers notes over outlines 6 and 7 for lecture exam 3.

What is compact (cortical) bone?

Dense, solid outer bone tissue found in all bones

What is another name for compact bone?

Cortical bone

Where is compact bone located?

Outer layer of all bones (especially diaphysis of long bones)

What is the main function of compact bone?

Provides strength, protection, and weight-bearing support

Why is compact bone important in ALL bones (not just long bones)?

It forms the strong outer shell that protects internal structures and supports the body

What is the periosteum?

Outer connective tissue covering of bone

What are the two layers of the periosteum?

Outer fibrous layer + inner osteogenic layer

What is the outer fibrous layer of the periosteum made of?

Dense irregular connective tissue

What is the function of the outer fibrous layer?

Protection and attachment site for tendons/ligaments

What is the inner osteogenic layer of the periosteum?

Cell layer with osteoblasts, osteoclasts, and stem cells

What is the function of the osteogenic layer?

Bone growth, repair, and remodeling

What are Sharpey’s (perforating) fibers?

Collagen 1 fibers that anchor periosteum to bone

Why are Sharpey’s fibers important?

Strengthen attachment of tendons and ligaments to bone

What does the periosteum contain?

Blood vessels + sensory nerves

Why is the periosteum important physiologically?

Growth in thickness + fracture repair + nutrient supply + pain sensation

What is an osteon?

Functional unit of compact bone

What is another name for an osteon?

Haversian system

What does an osteon look like structurally?

Cylindrical unit with concentric rings around a central canal

What is the central canal (Haversian canal)?

Channel running vertically through osteon

What does the central canal contain?

Blood vessels + nerves

What direction do central canals run?

Parallel to the diaphysis (long axis of bone)

What are lamellae?

Layers (rings) of calcified bone matrix

What are concentric lamellae?

Rings surrounding the central canal in an osteon

What are interstitial lamellae?

Remnants of old osteons between current osteons

What are circumferential lamellae?

Outer layers that wrap around the entire diaphysis

What are the 3 types of lamellae?

Concentric, interstitial, circumferential

What is a lacuna (plural: lacunae)?

Small space in bone matrix

What is found inside lacunae?

Osteocytes

What is an osteocyte?

Mature bone cell that maintains bone

What are canaliculi?

Tiny channels connecting lacunae

What is the function of canaliculi?

Allow nutrient and waste exchange between osteocytes

What are Volkmann’s (perforating) canals?

Horizontal canals connecting central canals

What are Volkmann’s function?

Allow blood vessels and nerves to travel across osteons

How are osteons arranged in compact bone?

Packed tightly side-by-side in the diaphysis

How do central canals and Volkmann’s canals work together?

Vertical + horizontal network for blood and nerve supply

Where are osteocytes located relative to lamellae?

In lacunae between lamellae

How do osteocytes get nutrients without direct blood supply?

Through canaliculi

What is the functional unit of compact bone?

Osteon

What structure carries blood vessels vertically?

Central (Haversian) canal

What structure connects osteons horizontally?

Volkmann’s canals

Where are osteocytes found?

Lacunae

What allows osteocytes to communicate and exchange nutrients?

Canaliculi

MAKE SURE TO KNOW THIS FIGURE!!!!

THERE IS NO ANSWER!!!

What is spongy bone?

Porous, lattice-like bone found inside bones

What are two other names for spongy bone?

Trabecular bone & cancellous bone

Does all bone contain spongy bone?

Yes

Where is spongy bone located relative to compact bone?

Inside, deep to compact bone

Where is spongy bone found in flat bones?

Between two layers of compact bone (interior)

Where is spongy bone found in long bones (femur)?

Epiphyses and metaphyses (ends of bone)

What are trabeculae?

Interconnecting rods/struts of bone

What do trabeculae form?

A lattice (honeycomb-like structure)

What fills the spaces between trabeculae?

Bone marrow (red or yellow)

What tissue exists between trabeculae?

Bone marrow (hematopoietic tissue)

What is hematopoietic tissue?

Blood-forming tissue

What is the function of hematopoietic tissue?

Produces RBCs, WBCs, and platelets

What is one major function of spongy bone structure?

Houses bone marrow for blood cell production

What is another major function of spongy bone?

Reduces bone weight while maintaining strength

How does trabeculae orientation help function?

Aligns with stress lines to resist forces (Wolff’s Law)

Do trabeculae contain osteons?

No

Do trabeculae contain central (Haversian) canals?

No

How are lamellae arranged in trabeculae?

Parallel layers (NOT concentric rings)

How are lamellae arranged in osteons?

Concentric rings around a central canal

Which is larger: trabeculae or osteons?

Trabeculae are thicker/larger

Do trabeculae have endosteum?

Yes (covered by endosteum)

Do osteons have endosteum?

Yes (lining internal canals)

Where are osteocytes located in trabeculae?

In lacunae within lamellae

Where are osteoblasts located in trabeculae?

On the surface (endosteum)

Where are osteoclasts located in trabeculae?

On the surface (endosteum)

What is the endosteum?

Thin cellular membrane lining internal bone surfaces

Where is the endosteum located?

Covers trabeculae, lines medullary cavity, lines canals

What is the function of the endosteum?

Bone growth, repair, and remodeling

How do osteoblasts affect trabeculae?

Build bone (add matrix)

How do osteoclasts affect trabeculae?

Break down bone (resorption)

How do osteoblasts and osteoclasts work together?

Balance bone formation and breakdown

How does this help calcium homeostasis?

Releases or stores Ca²⁺ in blood

What is bone remodeling?

Continuous process of bone breakdown and rebuilding

Which cells participate in bone remodeling?

Osteoblasts and osteoclasts

Is trabecular remodeling an example of bone remodeling?

Yes

What is another example of bone remodeling discussed?

Changes in proximal epiphysis/metaphyses femur during growth (toddler → adult)

What happens to trabeculae during toddler remodeling?

Reorganize along stress lines

Why is toddler remodeling beneficial?

Improves strength and efficiency for movement/weight-bearing

In epiphyses, which is more abundant: spongy or compact bone?

Spongy bone

Where is compact bone in epiphyses?

Thin outer layer

Where is spongy bone in epiphyses?

Inside (majority)

What defines a juvenile long bone?

Presence of an epiphyseal growth plate

What defines an adult long bone?

Absence of growth plate (epiphyseal line instead)

What is the epiphyseal growth plate?

Region of hyaline cartilage for bone growth

What is the epiphyseal plate made of?

Hyaline cartilage

What replaces the epiphyseal plate in adults?

Epiphyseal line

What can NO longer occur once the plate is gone?

Increase in bone length

What is the epiphyseal line?

Ossified remnant of the growth plate

What is the main function of the epiphyseal plate?

Longitudinal (lengthwise) bone growth

What is the medullary cavity?

Hollow space inside the diaphysis

What types of marrow can be in the medullary cavity?

Red marrow and yellow marrow

What fills the medullary cavity in very young individuals?

Red marrow

What is the function of red marrow?

Produces blood cells (RBCs, WBCs, platelets)

What happens to red marrow with age (~20+)?

Decreases (recedes)

What increases in the medullary cavity with age?

Yellow marrow

What is yellow marrow made of?

Adipose (fat) tissue

What is the function of yellow marrow?

Fat storage (can convert back to red if needed)