CARTILAGE AND BONE

• The 4 main functions of cartilage:

• Provides a strong but flexible support system
• Relieves friction between bones
• Resists compression and absorbs shocks
• Permits growth of the skeletal system



• The 3 types of cartilage and their locations:

• Hyaline
• epiphyseal plates
• articular surfaces of synovial joints
• thoracic cage
• upper respiratory passageways
• Elastic
• ear
• epiglottis
• Fibrocartilage
• intervertebral discs
• menisci and articular discs in some other synovial joints (e.g. TMJ)
• pubic symphysis



• The 3 components of cartilage:

• Cells
• Matrix (a gel containing chondroitin sulfates)
• Fibers (collagen, elastic)

• The 3 layers of the perichondrium:

• Outer fibrous layer of dense irregular CT
• Inner cellular layer of mitosing fibroblasts

• The 3 types of cartilage cells:

• Perichondrial fibroblasts
• Chondroblasts (cartilage forming cells)
• Chondrocytes (mature cartilage cells living within pale staining lacunae)

• The 2 methods of chondrogenesis:

• Appositional (peripheral) growth - from perichondrial fibroblasts
• Interstitial (central) growth - normal mitoses of chondrocytes within the matrix.

* No growth occurs in adult cartilages

• Most interesting fact: Unlike bone, cartilage is avascular and carries out metabolic processes by diffusion. This is because chondrocytes secrete antiangiogenesis factor which prevents blood vessel growth. AAGF is abundant in cartilagenous fishes in which cancers are extremely rare. It can now be synthesized using recombinant DNA techniques and is used in cancer therapy.
• At least 6 major functions of the skeletal system:

• Support
• Protection
• Leverage for locomotion
• Growth and self-repair
• Storage of minerals (esp. calcium) and lipids
• Production of blood cells (red, white and platelets)



• The 4 types of bone cells:

• Osteoprogenitor cells (stem cells that form osteoblasts)
• Osteoblasts (immature bone cells)
• Osteocytes ( mature bone cells)
• Osteoclasts (multinucleated giant cells that dissolve bony matrix)



• The 3 components of bone tissue:

• Cells
• Matrix (calcium phosphate + calcium hydroxide form crystals of hydroxyapatite which incorporate other calcium salts and ions (Na, Mg, F) providing a strong but inflexible inorganic substrate
• Collagen fibers (provide the organic framework for the formation of mineral crystals)



• The 2 types of ossification (next page):

• Intramembranous
• Intracartilagenous (endochondral)



• The 2 types of bone:

• Compact - dense, solid, peripheral bone
• Spongy - cavernous, trabeculated marrow bone



• The primary features of compact bone:

• Surrounded by a 2-layered periosteum
• outer fibrous (continuous with deep fascia) which gives rise to the penetrating fibers (of Sharpey) connecting the periosteum to the underlying circumferential lamellae.
• inner cellular (progenerative)
• Circumferential lamellae - layers of osteocytes and matrix that surround the circumference (periosteal lamellae) and line the marrow cavity (endosteal lamellae)
• Osteons (Haversian Systems) are the basic structural and functional units of compact bone consisting of:
• concentric layers of osteocytes and lamellae ...
• surrounding a central (Haversian) canal ...
• containing an artery and vein ...
• and receiving the perforating vascular canals (of Volkman) which transport blood to and from the marrow cavity.
• osteocytes maintain contact via tiny cytoplasmic extensions

(for the diffusion of nutrients and gases in the canaliculi of Haversian lamellae.

• interstitial lamellae are the remnants of old Haversian systems.



• The primary features of spongy bone:

• The presence of interlacing struts or spicules of bone called trabeculae.
• There are no osteons so nutrients and gases reach osteocytes via canaliculi.
• During normal growth, spongy bone is laid down faster by endosteal osteoblasts than it is broken down by osteoclasts (in Howship's lacunae).

• 10 diseases affecting the skeletal system:

• Acromegaly - excessive secretion of growth hormone after puberty leading to thicker bones.
• Dwarfism - a slowdown in epiphyseal plate growth leading to short stocky limbs though the trunk and genitalia are normal.
• Gigantism - excessive secretion of growth hormone before puberty.
• Marfan's Syndrome - excessive cartilage formation of the epiphyseal plates leading to extreme height and long, slender limbs.
• Osteoarthritis - degenerative joint disease resulting from excessive wear and tear or genetic predisposition.
• Osteomalacia - a softening of bone due to a decrease in mineral content; ricketts is characterized by a "bowlegged" appearance.
• Osteomyelitis - a painful bacterial infection of bone.
• Osteopenia - inadequate ossification leading to thinner, weaker bones.
• Osteopetrosis - a decrease in osteoclast activity causing an increase in bone mass.
• Osteoporosis - an increase in osteoclast activity causing a decrease in bone mass.