Skeletal System: Cartilages

• Skeletal systems include bones, cartilage, and joints which support the body, provide attachment sites, and store minerals
• Cartilage cushions joints, and bone replaces cartilage tissue during prenatal and childhood growth
• Bones are dynamic organs

Cartilages

• Found throughout the adult human body
• Play roles in support and movement
• Most bones are formed in cartilage first

Cartilage location in the body

• External ear
• Nose
• Articular joints
• Costal region
• Larynx, including the epiglottis
• Respiratory system
• Discs between the vertebrae
• Pubic symphysis
• Meniscus in the knee
• Connective tissue cartilage contains no nerves or blood vessels
• The perichondrium is a layer of dense connective tissue around cartilage helps provide growth and repair
• Cartilage tissue consists mostly of water (60-80%)

Cartilage Tissue Types

• Hyaline, elastic, fibrocartilage
• All consist of chondrocytes and extracellular matrix

Types of Cartilage

• Hyaline looks like frosted glass and has spherical chondrocytes and collagen
  • It is abundant
  • Functions to provide support through flexibility and resilience
  • Makes up articular cartilage and the attachments of the ribs to the sternum.
• Elastic cartilage has elastic fibers and collagen fibrils
  • It is more elastic than hyaline cartilage and can tolerate repeated bending
  • The epiglottis and outer ear are made of elastic cartilage
  • Fibrocartilage resists strong compression and strong tension forces
  • Intermediate between hyaline cartilage and dense regular connective tissue
  • The anulus fibrosus and the menisci of the knee are made of fibrocartilage

Cartilage Growth

• Appositional growth is growth from outside, active chondroblasts secrete matrix
• Interstitial growth is growth from within, chondrocytes divide and secrete new matrix
• Cartilage growth is rapid during development, childhood, and adolescence then stops in the late teens
• Healing is very limited in adults
• Calcified cartilage is not bone

Bones

• Organs composed of tissues like nervous, blood, cartilage, and epithelial.

Bone Functions

• Support the body with a hard framework
• Skeletal muscles attach to the bones by tendons and use the bones as levers to move the body
• Bones are protective casings for organs
• Reservoir for minerals, such as calcium and phosphate
• Contain red and yellow bone marrow, which makes blood cells or stores fat
• Osteoblasts influence blood sugar regulation and energy metabolism via osteocalcin secretions

Bone Tissue

• A connective tissue with cells separate by extracellular matrix
• Organic and inorganic components, with small amounts of tissue fluid

Components of Bone Tissue

• Organic components account for 35% of the bone mass and contribute to flexibility via collagen fibres
• Inorganic components account for 65% of the bone mass and contribute to compressional strength via mineral salts
• The mineral salts are hydroxyapatites or calcium phosphate

Types of bone cells

• Osteoprogenitor: Stem cells that differentiate to create bone-building osteoblasts
• Osteoblasts: Matrix is secreted and builds bones
• Osteocytes: Function to keep bones healthy/maintain
• Osteoclasts: Resorption of bone

Bone classification by shape

• Long, short, flat, or irregular

Long Bone structure and location

• Considerably longer than they are wide
• Limbs are long bones like the fingers and toes
• The tubular diaphysis is the shaft and forms the long axis of the long bone
• Epiphyses are the bone ends
• Covered by articular cartilage, which is thin hyaline cartilage
• Epiphyseal line is a remnant of the epiphyseal plate
• Nutrient artery supplies the diaphysis, epiphyseal arteries/veins serve each epiphysis
• Medullary cavity is the very center of the diaphysis of long bones and is filled with yellow bone marrow.
• Periosteum covers the outer surface of bones, comprised of a superficial layer of dense irregular connective tissue and a deep osteogenic layer containing bone depositing/destroying cells called osteoblasts/clasts.
• Periosteum is secured to the underlying bone via perforating collagen fiber bundles.
• Endosteum covers internal bone surfaces and also contains bone depositing/ destroying cells called osteoblasts/clasts.

Design and Bone stress

• The structure of bone reflects the stresses, bones are compressed by weight-bearing and muscles
• A hollow cylinder is stronger than a solid rod of equal weight
• Flat bones consist of two plates of compact bone separated by a layer of spongy bone, compact bone is the bread, and the spongy bone is the filling

Bone Markings

• Reflect the functions of bone and muscles
• Landmarks help identify sites of muscle attachment, articulation, and passage of blood vessels and nerves