Bone Tissue (pt.1)

Bone Tissue: Overview

• connective tissue

• dynamic and alive

• capable of change in response to different stimuli or external mechanical forces

Bone Remodeling

building of new bone

breakdown of old bone

Bone: Function

• support

• protection

• assistance in movement

• mineral homeostasis

• blood cell production: red bone marrow

• triglyceride storage: yellow bone marrow

Bone Structure: Long Bones

Diaphysis

Epiphysis

Metaphysis

Epiphyseal Plate

Epiphyseal Line

Articular Cartilage

Periosteum

Medullary Cavity

Endosteum

Diaphysis

Bone Structure;

body or shaft of the bone

Epiphysis

Bone Structure;

the proximal and distal ends of bones

Metaphysis

Bone Structure;

region between the diaphysis and epiphysis

where growth can occur

Epiphyseal Plate

Bone Structure;

growth plate, area of active growth

located in metaphysal area

Epiphyseal Line

Bone Structure;

bone growth has ceased

Articular Cartilage

Bone Structure;

cartilage covering epiphysis at a joint

reduces friction, absorbs shock, avascular

Periosteum

Bone Structure;

tough connective tissue surrounding bone where cartilage is absent

Medullary Cavitty

Bone Structure;

hollow space within the diaphysis of long bones containing fatty yellow marrow and blood vessels

decreases bone mass

Endosteum

Bone Structure;

connective tissue membrane that lines the medullary cavity and the internal spaces of spongy bone

single layer of osteoprogenitor cells and connective tissue

What is bone tissue made of?

• 15% water

• 30% collagen fibers

• 55% crystallized mineral salts

Calcification

mineral salts are deposited and crystallize along the collagen and extracellular matrix material

hardness depends on the crystallized inorganic mineral salts

flexibility depends on the collagen fibers

Osteoprogenitor Cells

stem cells of the bone

the only bone cells that divide and produce osteoblasts

found in the periosteum, endosteum, and canals containing blood vessels within the bone

Osteoblasts

build bone, synthesize and secrete collagen fibers and organic compounds that build the ECM

trapped in ECM and transition to osteocytes

-BLAST

means it secretes/creates ECM

Osteocytes

mature bone cells

maintain daily metabolism

trapped in ECM

-CYTE

mean the cell that maintains or monitors the tissue

Osteoclasts

huge cells from fusion of multiple monocytes

concentrated in the endosteum

release lysosomal enzymes and acids that digest the protein and mineral components of the bone’s ECM

Bone Resorption

part of normal development, maintenance, and repair of bone

helps regulate blood calcium

-CLAST

in bone means cells that breakdown ECM

Compact Bone

• strongest type of bone

• dense with few spaces

• beneath periosteum of all bones

• bulk of the diaphysis of long bones

• provides protection, support, and resists strains from weight and movement

Osteons (Haversian Systems)

Compact Bone;

repeating structural units of concentric bone lamellae arranged around a osteogenic canal

Concentric Bone Lamellae

Compact Bone;

circular plates of mineralized ECM surrounding the osteonic canal containing blood vessels and nerves

Bone Lacunae

Compact Bone;

small spaces between concentric bone lamellae containing osteocytes

Bone Canaliculi

Compact Bone;

small channels radiating from the bone lacunae filled with extracellular fluid/interstitial fluid

• connects bone lacunae

• contain finger-like projections of osteocytes

• interconnected system of canals throughout the bone creating a route for nutrients oxygen to reach osteocytes and for waste removal

Interstitial Bone Lamellae

Compact Bone;

areas of bone between osteons

remnants of older bone lamellae that have been partially destroyed during bone rebuilding and growth

Perforating Canals

Compact Bone;

transverse through compact bone bringing blood vessels and nerves from the periosteum to the osteonic canals and bone surrounding the medullary cavity

External Circumferential Bone Lamellae

Compact Bone;

arranged around the entire outer circumference of the diaphysis deep to the periosteum

Internal Circumferential Bone Lamellae

arranged around the inner circumference of the compact bone around the medullary cavity

Organization of Osteons

Compact Bone;

dynamic

change overtime due to stresses applied to the bone such as walking, strenuous physical activity, previous bone injuries or fractures

Spongy Bone (Trabecular Bone): Overview

• made up of bone trabeculae: bone lamellae in irregular pattens of thin columns

• no osteons present

• lots of open space between trabeculla

• located in the interior of a bone and projecting into the medullary cavity

• protected by an outer layer of compact bone

Bone Trabeculae

Spongy Bone;

• consists of: bone lamellae, osteocytes in lacunae, canaliculi

• lined by endosteum in medullary cavity

• oriented along lines of strain

• trabeculae are not random

• orientation is dynamic

• bone marrow fills the space between trabeculae

What is in the bone marrow?

red marrow = produce RBC

yellow marrow = adipose tissue (primarily)

many blood vessels that nourish the osteocytes

Where is spongy bone found?

found in all types of bone

makes up the interior of short, flat, sesamoid, and irregular bone

in long bones = make up interior of the epiphysis and a narrow rim bordering the medullary cavity

Spongy Bone: Functions

decreased weight/mass of bone improving movement

protects red marrow for blood cell production (Hemopoiesis)

Hemopoiesis

• process by which the body creates all of its mature blood cells and blood components

• occurs in pelvic bones, ribs, sternum, vertebrae, skull, proximal ends of long bones such as the femur and humerus