Bones

Function of the skeleton

1. Protection

2. support

3. Anchorage

4. Mineral support

5. Blood cell formation

6. Triglyceride (Fat) storage

7. Hormone production

Two types of bone

1. Spongy

2. Compact

Compact bone

Dense outer layer

Spongy bone

• A honeycomb of small needle like flat pieces

  • These are called trabeculae

• Find bone marrow in the open spaces of spongy bone

Trabeculae

Is the honeycomb pieces of the spongy bone

What is bone made of

All bone is collagen that is mineralized

Never see spongy bone by itself

• Always incased in compact bone

• If you do see this them something is wrong

Long bones consists of 1 diaphysis and two epiphysis

Diaphysis is capped by epiphysis

Diaphysis

• Shaft of the long bone

• Relatively thick collar of compact bone around the medullary cavity

Medullary cavity

Middle hollow part of the diaphysis

it contains yellow marrow instead of bone tissue

Epiphysis

• Compact bone is the exterior

• Interior contains spongy bone

• One or two depending on the bone

• Covers the joint surface to cushion

Epiphyseal line

• Where diaphysis and epiphysis meet

• Shows that the long bone is done growing

Periosteum

• Double layer membrane that covers the external surface

• Covers the entire bone except joint surface

• Connective tissue membrane

Endosteum

• Covers the trabeculea of spongy bone

• Lines the canals that pass through the compact bone

Perichondria

• Dense irregular tissue

• Covers articular cartilage

Articular cartilage

• covers most the epiphysis

• Hyaline cartilage

Sharpeys fibers (perforating fibers)

Strong collagen fibers that anchor the periosteum into the underlying bone (compact bone)

Cartilage covers areas of

high friction

Cells of bone tissue

Osteoprogenitor cell → Oseoblast → Osteocytes

Osteoclasts

Osteoprogenitor

• Mitotically active stem cell

• Found in periosteum and endosteum

Osteoblast

• Builds bone

• Lay down cartilage then mineralizes it

• Between tissue and bone

• Responsible for bone growth

• Matrix synthesizing cell

Osteocytes

• Mature bone cell

• Monitors and maintains the bone matrix

Osteoclasts

• Bone- resorbing cell

• Breaks down bone

• Has multiple nuclei → Important to activate osteoclasts

Cells from the bone cell lineage

• Osteoprogenitor cell

• Osteoblasts

• Osteocyts

Cell from white blood cell lineage 

Ostoclasts

Bone lining cells

• flat cells found on bone surfaces

• where bone remodeling is not going on

• Thought to help maintain matrix

Osteons

• Function unit of compact bone

• “Tree rings” 

• Made up of concentric layers of mineralized collagen

Compact= Cortical=Lameller bone

What is cortical

Cortical is the outer layer of the bone

Lamella

• A single osteon

• Each layer of the lamella, the collagen fibers go different directions. This helps it to withstand tensile forse and resist twisting

Central canal

• Runs through the core of each osteon

• Contains small blood vessels and nerve fibers

Perferating canals (Volkmann’s canal)

• Connect the central canals to other osteons

• Connects the blood and nerve supply of the periosteum to the central canals and the medullary cavity

Lacunae

• Spider shaped osteocytes at the junction of the lamella

• Hair like canals called canaliculi radiate from the lacunae, connecting them to each other

Intersicial lamella

• Lamella between osteons 

• Lies between intact osteons and incomplete lamella

• either forming osteons or are remnants of osteons that have been cut through by bone remodeling

Circumferential lamella

• located just deep of the periosteum and just superficial to the endosteum

• Covers the whole diaphysis

• Helps resist twisting of the long bone

Short, irregular and flat bone structure

• Still contains spongy bone covered by compact bone

• Contains bone marrow beetween the trabecullae but does not have a defined marrow cavity

• Hyaline cartilage covers their surfaces