Chapter 6

Skeletal cartilage

Made of highly resilient, molded cartilage tissue that consists primarily of water

Perichondrium

-layer of dense connective tissue
-contains blood vessels for nutrient delivery to cartilage

Growth of cartilage/bones include

-appositional growth
-interstitial growth

Appositional growth

-adding new cartilage or bone on top of pre-existing bone or cartilage (deposition)
-life long but slows down when we get older
-always occurs under a membrane with lots of blood vessels (chondrogenic or osteogenic)

Interstitial growth

-growth from within (inside out)
-occurs in hyaline cartilage
-in the bone and stops at ages 18-25

Blasts

Cells that add bone (osteo-) or cartilage (chondro-)

Hyaline Cartilage

-provide support, flexibility, and resilience
-joints, ribs, larynx, nose tip
-most abundant type

Elastic Cartilage

-contains elastic fibers
-ear and epiglottis

Fibrocartilage

-thick collagen fibers
-menisci of knee and vertebral discs

Appositional Growth

-cartilage forming cells in perichondrium secrete matrix against external face of existing cartilage
-new matrix laid down on surface of cartilage

Interstitial Growth

-Chondrocytes within lacunae divide and secrete new matrix, expanding cartilage from within
-New matrix made with cartilage

Functions of Bones

-support
-protection
-movement
-mineral/growth factor storage
-blood cell formation
-triglyceride storage
-hormone production

Calcium

-needed for all cell activity
-muscle contraction
-nervous system
*once absorbed extra calcium is put on the bone

Axial Skeleton

-long axis of the body
-skull, vertebral column, rib cage

Appendicular Skeleton

-bones of upper and lower limbs
-girdles attaching limbs to axial skeleton

Compact Bone (lamellar)

Dense outer layer on every bone that appears smooth and solid

Spongy Bone (Trabecular)

Made up of a honeycomb of small needle-like or flat pieces of bone called trabeculae
*spaces between trabeculae are filled with red or yellow bone marrow

Structure of short, irregular and flat bones

thin plates of spongy bone covered by compact bone

Structure of long bones

have a shaft (diaphysis), bone ends (epiphysis), and membranes

Diaphysis

Tubular shaft that forms long axis of bone

Metaphysis

Located between diaphysis and epiphysis

Epiphysis

Ends of long bones that consist of compact bones externally and spongy bone internally

Periosteum

White double-layered membrane that covers external surfaces except joints

Fibrous Layer

Outer layer consisting of dense irregular connective tissue consisting of Sharpey's fibers that secure to bone matrix

Osteogenic Layer

Inner layer abutting bone and contains primitive osteogenic stem cells that rise to all bone cells

Endosteum

-delicate connective tissue membrane covering internal bone surface
-covers trabeculae of spongy bone

Hematopoietic Tissue

Red marrow found within trabecular cavities of spongy bone and diploe of flat bones such as the sternum

Cells of Bone Tissue

-osteogenic cells
-osteoblasts
-bone lining cells
-osteoclasts
-osteocytes

Osteogenic Cells

-called osteoprogenitor cells
-mitotically active stem cells in periosteum and endosteum

Osteoblasts

bone forming cells that secrete unmineralized bone matrix called osteoid

Osteocytes

Mature bone cells in lacunae that no longer divide

Bone lining cells

Flat cells on bone surfaces believed to also help maintain matrix

Osteoclasts

Derived from same hematopoietic stem cells that become macrophages

Osteon

Structured unit of compact bone

Central Canal (Haversian)

Runs through core of osteon

Perforating Canals (Volkmann's)

Canals lined with endosteum that occur at right angles to central canal

Lacunae

Small cavities that contain osteocytes

Canaliculi

Hair-like canals that connect lacunae to eachother and to central canal

Interstitial Lamellae

-lamellae not part of osteon
-Some fill gaps between forming osteons; others are remnants of osteons cut by bone remodeling

Circumferential Lamellae

Deep to periosteum but superficial to endosteum, these layers of lamellae extend around surface of diaphysis

Organic compounds in bone

-osteogenic cells
-osteoblasts
-osteocytes
-bone lining cells
-osteoclasts
-osteoid

Osteoids

Make up 1/3 of organic bone matrix, secreted by osteoblasts

Inorganic compounds in bones

-Hydroxyapatites (mineral salts)
-responsible for hardness and resistance to compression

Ossification (osteogenesis)

-Process of bone tissue formation
-begins at 2 month
-postnatal growth occurs until early childhood
-bone remodeling/repair are lifelong

Endochondral Ossification

-forms essentially all bones inferior to base of skull except clavicle
-breakdown of hyaline cartilage
-begins at primary ossification center

Intramembranous Ossification

-Begins with in fibrous connective tissue membranes formed by mesenchyme cells

5 zones of epiphyseal plate

-resting (quiescent) zone
-proliferation (growth) zone
-hypertrophic zone
-calcification zone
-ossification (osteogenic) zone

Resting (quiescent) zone

Area of cartilage on epiphyseal side of epiphyseal plate that is inactive

Proliferation (growth) zone

-area of cartilage on diaphysis side of epiphyseal plate that is rapidly dividing
-new cells formed moving upward, pushing epiphysis away from diaphysis, cause lengthening

Ossification zone

chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction

Bone remodeling

-about 5-7% bone mass is recycled each week
-spongy: 3-4 yrs
-compact: 10yrs
-consists of bone deposit and bone resorption

Remodeling units

packets of adjacent osteoblasts and osteoclasts coordinate remodeling process

Parathyroid Hormone

produced by parathyroid glands in response to low calcium levels

Calcitonin

Produced by parafollicular cells of thyroid gland in response to high levels of blood calcium levels

Calcitriol

Active form of vitamin D

Wolf's Law

Bones grow or remodel in response to demands placed on them

Fractures

breaking of bone
*during youth-result from trauma
*old age-due to bone thinning

Comminuted Fracture

-bone fragments in 3+ pieces
-common in the age where bones are more brittle

Compression Fracture

-bone is crushed
-common in porous bones

Spiral Fracture

-ragged break occurs when excessive twisting forces are applied to a bone
-common in sports

Epiphyseal Fracture

-epiphysis separates from the diaphysis along the epiphyseal plate
-occurs where cartilage cells are dying and calcification of the matrix is occurring

Depressed Fracture

-broken bone portion is pressed inward
-typical of skull fracture

Greenstick Fracture

-bone breaks incompletely; one side of the shaft breaks while the other side bends
-common in children whose bones have more organic matrix/flexibility

Reduction

Realignment of broken bone ends

Closed Reduction

Physician manipulates to correct position

Open Reduction

Surgical pins or wires secure ends

Immobilization

Cast or traction is needed for healing

Fracture Repair

-hematoma formation
-fibrocartilaginous callus formation
-bony callus formation
-bone remodeling

Hematoma Formation

-torn blood vessels hemorrhage forming mass of clotted blood
-site is swollen, painful and inflamed

Bony Callus Formation

Callus is converted to bony (hard) callus of spongy bone

Bone Remodeling

Final structure resembles original structure

Bone Disorders

-osteomalacia and rickets
-Osteoporosis
-Paget's disease

Osteomalacia

-bones are poorly mineralized
-osteoid is produced, but calcium salts not deposited
-soft, weak bones
-pain upon bearing weight

Rickets

-Otseomalacia of children
-bowed legs due to enlargement bone ends
-caused by vitamin D deficiency or insufficient dietary calcium

Osteoporosis

-group of diseases in which bone resorption exceeds deposit
-matrix is normal; bone mass decline