Bones and Skeletal Tissues

Structure and Function of

Cartilage and Bone

Cartilage (review)Characteristics

– Resists tension AND compression– Lots of collagen (strong) AND elastic fibers

(flexible)– High content of proteoglycans 80% water

(resiliency/spring properties)– No nerves or blood vessels– Chondroblasts make matrix until end of human

adolescence– Mature Chondrocytes found in cavities called

lacunae (pit)– Surrounded by the perichondrium (dense irregular

connective tissue) that serves to:• Resists outward expansion• Nourish cartilage tissues

Light Micrograph of Joint (Articular Surface)

Hyaline Cartilage (review)

• Looks glassy (hyalin = glass)• Few chondrocytes, all found in

lacunae• Mostly matrix – lots of collagen

Hyaline Cartilage (add notes)

• Provides flexibility w/resilience• Most abundant skeletal cartilage• Locations:

– Articular – covers the ends of long bones, moving joings

– Costal – connects ribs (sternal)– Respiratory –in larynx (voicebox),

reinforces air passages of lungs– Nasal – supports the nose

Elastic Cartilage (review)

• Looks almost identical to hyaline BUT more elastic fibers more flexible!

• Matrix appears more fibrous• More lacunae, closely spaced.

Elastic Cartilage (add)

• Elastic fibers allows for repeated “bending”• Found in:

– the external ear– Epiglottis (flap closes in larynx when we swallow)

Hyaline Cartilage

Elastic Cartilage

Fibrocartilage (review)

• Intermediate between dense regular CT and hyaline

• Consists of rows of chondrocytes and collagen fibers

• Compressible AND resists tension

Fibrocartilage (add)

• Due to compressibility, found in areas that need padding due to stretch/pressure:– menisci (singular: meniscus) of the knee – intervertebral discs

Bones and Cartilages of the Human Body

Figure 6.1

Growth of Cartilage

• Appositional – cells in the perichondrium secrete matrix at the surface of existing cartilage – Grows “outward”

• Interstitial – lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within– Grows from the inside of tissue• Area of appositional growth (black arrows)

• Area of interstitial growth (white arrows)

Function of Bones

• Support – “framework” that supports the body; cradles soft organs

• Protection –protective case for brain, spinal cord, vital organs

• Movement – levers for muscles• Mineral storage – reservoir for minerals,

especially calcium and phosphorus• Blood cell formation – hematopoiesis

occurs within the marrow cavities of bones

Bone Composition(organic)

Osteogeniccells

• mitotic stem cells in membranes

covering bones that create other bone

cells

4 cell types:

Osteoblasts:• Young, bone cells

that makes un-mineralized bone matrix, “osteoid” (ground substance, collagen, glycoproteins,etc.)

Osteocytes:• mature, bone

cells that maintains osteoid

Osteoclasts:• Large cells that

dissolve and break-down bone and its osteoid

Bone Composition(inorganic)

Mineral Salts (Hydroxyapatites)• 65% bone by mass• mainly calcium phosphate,

deposited around collagen of osteoid

• responsible for hardness and compression resistance of bone

• Deposited by osteoblasts, source of calcium and phosphate in blood plasma.

Skeletal Classification

• Axial skeleton – long axis of body– bones of the skull,

vertebral column, and rib cage

• Appendicular skeleton – bones of the limbs and girdle (shoulder, hip)

Classification of Bones: By Shape

• Long bones – longer than they are wide (ex. humerus)

• Named for relative length and width, not size (ex. fingers are also long bones!)

• Short bones– Cube-shaped

bones of the wrist and ankle

– Bones that form within tendons (ex. patella)

Classification of Bones: By Shape

• Flat bones – thin, flattened, and a bit curved

• (ex. sternum, ribs, shoulder blades, skull)

Figure 6.2c

Classification of Bones: By Shape

• Irregular bones –complicated shapes

• (ex. vertebrae and pelvis)

Classification of Bones: By Shape

Bone Textures

Compact bone – dense outer layer made up of osteons. Very supportive.

Spongy bone – honeycomb of trabeculae filled with yellow marrow (fat) or red bone marrow (hematopoietic)

Trabeculae: - needle-like extensions of bone - disperse pressure without much weight - resists compression on ends of bones - marrow fills in between spaces

Membranes of Bones

Periosteum: double-layered membrane on external surface of bones

Inner layer:osteogenic stem cells that differentiate (specialize) into bone cells like osteoblasts (bone

forming) or osteoclasts (bone

dissolving) cells.

Outer layer: protective, fibrous dense irregular connective tissue

Porous with “nutrient foramens” to supply bone with nerves, lymph, and blood vessels

Attach periosteum to bone

Endosteum: delicate membrane covering internal surfaces of compact bone (next to marrow) or the trabeculae of spongy bones

Structure of Long Bone

• Consists of a diaphysis (shaft) and an epiphyses (ends)

• Diaphysis – – Forms the axis – Compact bone that

surrounds hollow medullary cavity that contains yellow marrow (fat)

Structure of Long Bone

• Epiphyses– compact bone exterior;

spongy bone interior– joint surface covered w/

articular (hyaline) cartilage cushions opposing bone

ends during movement– Epiphyseal line, for bone

lengthening, separates the diaphysis from the epiphyses

Structure of Long Bone

Structure of Short, Irregular, and Flat Bones

• Thin periosteum-covered compact bone on the outside with endosteum-covered spongy bone (diploë) on the inside

• Have no diaphysis or epiphyses

• Bone marrow fills spaces within trabeculae

Location of Hematopoietic Tissue (Red Marrow)

• In infants– Found in the medullary cavity of long bones

and all areas of spongy bone • In adults

– Found in the diploë of flat bones, hip, and the head of the femur (thigh) and humerus (upper arm)

Micro-anatomy of Compact BonesHaversian system or Osteons: the structural unit of compact bone

Osteon

Haversian or Central Canal: central channel containing blood vessels and nerves

Volkmann’s canals: connects blood and nerve supply of the periosteum to the Haversian canal

Volkmann’s Canals

periosteum

Lamella: an osteon’s weight-bearing, concentric matrix tubes (mostly of collagen)

Micro-anatomy of Compact Bones

Circumferential lamella – extend under periosteum around the entire circumference of diaphysis

Interstitial lamella: collagen matrix that fills in gaps between osteons

Micro-anatomy of Compact Bones

Osteocytes: trapped in cavities called lacunae, in between lamella

Canaliculi: hairlike canals that connect lacunae to each other and the central canal

Osteoblasts:

• Initially make matrix that hardens around them (lamella).

• As they mature, osteoblasts become osteocytes.