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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.