• Strength in multiple directions bc of latticework and space In/ around it, has red bone marrow which is essential for the making of blood cells (haematopoiesis)

Long bone vs others

Long bones =

share many common features
Irrespective of location as function is similar…
All assisst with Mobility!

Other bones =

Each Irregular, Short, Sesamoid, and Flat bone is unique…
Structure & features are based on location & function
No common features on the bone

Macroscopic appearance of bone and their functions

Bone Surface Features

• Rough areas, elevations, processes, grooves, depressions & openings

Provide a Functional Purpose

• Site of attachments

> Tendons/Muscles, Ligaments (stabilise a joint), Joint Capsule (structure that surrounds a whole joint)

• Articular surfaces

>Joint architecture determines movement

• Passageway for nerves & vessels

Gross anatomy of the long bone

Diaphysis = Shaft/ hollow structure

• Made of Cortical (compact) bone

Epiphysis = Ends of bone

• Contains Trabecular (spongy) bone

>epiphysial line if an adult and become bone or a plate that is made of cartilage if person is till growing

Metaphysis = Between Epiphysis & Diaphysis

• Contains Trabecular (spongy) bone

Medullary Cavity = Marrow cavity in diaphysis

>hollow except for yellow bone marrow where fat and energy is stored

Articular Cartilage = Covers epiphyses

• Smooth frictionless movement at joint

Fibrous tissues/membranes that cover the inside or outside of the bone
Periosteum only surrounds the actual bone not the joint, and will end where the articular cartilage begins (this cartilage allows for smooth frictionless joint)

Bone as a connective tissue

Bone is continuously changing, it is strong and semi-rigid in order to hold us and maintain our structure, but also be flexible and have some bend (as a result of fibres)

Suppourtive connective tissues

Bone is a supportive connective tissue
Supportive Connective Tissue = provide structural strength and protect soft tissue; few distinct cell types with densely packed fibres

• Bone – matrix is rigid & calcified (deposition of calcium mineral salts)

• Cartilage – matrix is firm but gelatinous (deposition of chondroitin polysaccharides)

Bone tissue

Bone is a Supportive Connective Tissue

• Cells: Osteoprogenitor, Osteoblasts, Osteocytes & Osteoclasts

• Extracellular matrix:

> Organic components (material cells are making) = Collagen fibres

> Inorganic components (body/ DNA doesn’t create or code for, get them thru diet) = Mineral salts, make bone hard

Bone extracellular matrix

Organic components (osteoid):

• Synthesized and secreted by Osteoblasts (secretes material for basic soft model of bone)

Collagen type I

Inorganic Matter:

• Harvested from surrounding blood

• Calcium and Phosphorous Mineral Salts

Mineralization (Calcification):

• Hardening of bone extracellular matrix from the soft bone formed by osteoblasts

• Mineral salts bind to collagen, forming crystals that make bones physically hard

Bone cells

The first THREE cells are from one bone cell that grows over time (one cell lineage)

Osteoprogenitor Cell (osteogenic cell)

• Mesenchymal stem cell ( stem cell means cell that has the ability to turn into something else, mesenchymal means it has ability to turn into 3 distinct pathways, either bone, fat (adipocyte) or chondrocyte in cartilage)

• Only bone cell to undergo mitosis (i.e. divide) meaning it has being relied on to keep replenishing bone cells

• Some will become osteoblasts (a process called differentiation)

• Location: lines the surface/edges of bone

• Under Periosteum & Endosteum

Osteoblast

• Bone forming cell, after osteoprogenitor cells have received signal

• Synthesises and deposits the organic bone matrix (collagen fibres)

• Initiates calcification – impregnation of inorganic substances into bone matrix (hardens bone)

• Become (differentiate) osteocytes when encased/trapped in own bone deposits and needs branches to go through crystal matrices in bone to get nutrients

• Location: lines the surface/edges of bone, like osteoprogenitor cell

• Under Periosteum & Endosteum

Osteocyte

• Maintain bone microenvironment

• Delicate cellular projections (fingers) create a sensory network through bone matrix

• Regulate other bone cells

• Location:

• Cell Body = inside small cavities in bone (Lacunae) that were made when the bone was being formed

• Cellular Projections = travel through small canals (Canaliculi) that are extension of cells cytoplasm

Osteoclast

• Differentiate from haematopoietic stem cell (NOT from the same family as the previous 3 bone cells) as they are white blood cells

• Fusion of monocyte/macrophage type cells that come together to make a giant macrophage, that when told to live on a bone becomes an osteoclast

• Large multinucleated cell as it forms from many cells coming together with ruffled basal surface

• Creates a suction (sealing zone) to attach to bone to break down bone matrix (i.e. Resorption)

• Releases lysosomal enzymes and acids

• Location: Edge of bone in resorption pits

Osteon Components (A.K.A. Haversian System) from compact bone

Osteons are vertical tube-like bony constructs arranged in parallel

• You will ONLY find Osteons in Compact Bone

• Compact bone is a construct of multiple osteons

Each Osteon contains:

• Haversian (central) canal

A single canal for vessels
Supply of nutrients/removal of waste for bone cells

• Concentric Lamellae

‘Layers’ of bone ‘rings’ around the Haversian canal

• Lacunae

Cavities in lamellae containing the osteocyte cell body

• Canaliculi

Canals through lamellae containing osteocyte cellular

Compact bone also contain:

• Volkmann's canals – ‘Horizontal’ canals for vessels connecting adjacent osteons for carrying nutrients and waste

• Interstitial lamellae – Old osteons no longer containing a Haversian canal

> No longer layered around a central canal

> You will find only ‘interstitial lamellae’ in spongy/trabecular bone

How osteons form

Osteons are created during the process of bone formation and maintained or updated during the bone remodelling process

Starts with Vessels (blood and lymph), nerves
Osteoblasts come to the area around vessels due to growth factor being released into the local environment
Osteoblasts begin to lay down bone
Osteoblasts lay down more bone…Osteoblasts lay down so much bone they trap themselves in small cavities The small cavity is called a Lacunae THEN Osteoblasts now must differentiate into Osteocytes to survive
Osteoclasts exit the blood stream and resorb (remove) bone around vessel = Forms the Central / Haversian canal
An Osteoblast enters the Harversian Canal and fills in a single ring/layer of bone (lamellae)
Another Osteoblast creates another layer of bone within Haversian Canal (Concentric lamellae) Old osteoblast trapped in ‘Lacunae’ differentiates to form Osteocyte
Osteoblasts lay down so much bone they trap themselves in small cavities The small cavity is called a Lacunae -> Osteoblasts now must differentiate into Osteocytes to survive
Osteocyte projections form and tunnel through the bone to receive nutrients, remove wastes & communicate = Canals in bone are “Canaliculi”

Trabeculae (main functional unit of spongey bone)

Trabeculae is found in spongey/ trabecular bone, in the heads of bones

• Trabeculae are individual “strut” like bony units

• Spongy (i.e. Trabecular) bone is a latticework of

trabeculae

• You will ONLY find trabeculae in spongy bone (as cortical bone is too dense with no space for struts)

• Each Trabeculae contains:

Lamella (layers of bone) arranged in plates or sheets
Much like interstitial lamella
Lacunae & Canaliculi for osteocytes

• Trabeculae do NOT have

Concentric lamella (layered rings of bone)
A Haversian (central) canal as the cells can grab on the blood vessels from the surrounding area

Bone cell nutrition

Osteoprogenitors, Osteoblasts and Osteoclasts

• Located at edge of bone

• Diffusion of nutrients from local fluid Environment

• Osteocytes

• Located in lacunae (encased in solid bone matrix)

• Nutrients do NOT diffuse through calcified matrix

• Delicate Osteocytes projections travel through canals in bone (canaliculi) connecting with blood vessels outside of bone (red bone

marrow) or within the Haversian (central) canal

Cartilage is also a Supportive Connective Tissue

• Function:

Maintains shape
Resist compression & absorbs shock
Provides smooth surface to minimise friction (articular cartilage in long bone does this and resists compression)

• Cells:

• Chondroblast: Secrete cartilage extracellular matrix

• Chondrocyte: Chondroblast trapped in cartilage matrix