Bone and Cartilage - A&P
Bone strength is due to
combination of minerals (in matrix) + collagen fibers (protein) (reinforced concrete - need "concrete" and "rebar")
Bone cells:
osteoprogenitor cells osteoblasts osteocytes osteoclasts
decreased bone strength
sedentary lifestyle malnutrition casting a fracture astronauts in space
Fibrocartilage
textured look - fibrous appearance Weight bearing Forms intervertebral disks, pubic symphysis, menisci (in knees)
Canaliculi (compact bone)
tiny channels/tunnels that connect lacunae House cytoplasmic projections (like dendrites) from osteocytes Projections allow osteocytes (can detect mechanical stress, need to communicate) to communicate and move nutrients/wastes around
Osteoporosis
"porous" bones
Periosteum (long bone anatomy)
- Covers surface of bones except where articular cartilage exists - Two layers: Outer, fibrous layer; Inner, cellular layer
Osteoblasts
- Cuboidal shape - Synthesize and secrete osteoid - Osteoid → calcifies; trapping osteoblasts → some become osteocytes
Perforating canals (Volkmann's) (compact bone)
- Entry and exit place from the central canal - Oriented perpendicular to central canals - Also contain blood vessels and nerves - Connect various central canals of osteons
endochondral ossification process
- Hyaline cartilage invaded by osteoblasts, capillaries - Bony collars form at diaphysis - Ossification center forms in center - Spongy bone → cortical bone - Secondary ossification centers in epiphysis
Interstitial lamellae (compact bone)
- Incomplete osteons, no central canal - Bits of compact bone between osteons - Leftover bits from repetition of osteons
Chondroblasts (in hyaline cartilage)
- Located just under perichondrium - Produce cartilage matrix; SEMISOLID - Once encased in matrix → become chondrocytes
Effects of exercise on bone
- Mechanical stress is critical for bone strength - Weight bearing/concussive force → increased bone density - Resistance training: more effective than cardiovascular activity - Bone strengthens to activity level
intramembranous ossification process
- Mesenchymal cells in fetal skeleton → begin maturing: early capillaries, early osteoblasts cluster together to form ossification centers in fetal skeleton - Osteoblasts secrete osteoid → mineralizes Trapped osteoblasts → become osteocytes - Extends outward; osteoblasts → osteoid → mineralizes → trapping → osteocytes - Spongy bone → cortical bone - Capillaries trapped in center → become red marrow (tissue that makes blood cells)
Inorganic portion (of bone matrix)
- Salts - Deposit around collagen fibers - Primarily calcium phosphate + calcium hydroxide → hydroxyapatite - Other salts - calcium carbonate - Ions - sodium, magnesium, sulfate, fluoride
Fracture healing time varies by:
- age (children - 3 weeks; adults - 8-12 weeks) - fracture type (simple nondisplaced: faster healing) - presence of infection (open/compound: longer healing) - concurrent diseases (diabetes, osteoporosis, etc)
sex hormones (bone health)
- estrogen, progesterone, testosterone - critical for bone health: stimulate bone formation - stimulate osteoblasts
Long bones (bone classification)
- most common - Greater in length than in width - Have an elongated shaft - diaphysis Ex: bones of upper and lower arms and legs, palms, fingers, toes
Osteons (Haversian systems)
- subunit of compact bone - cylindrical structures with concentric circles within - oriented parallel to diaphysis of long bone
Steps of fracture repair
1. Hematoma formation 2. Fibrocartilaginous callous formation 3. Bony callous formation 4. Bone remodeling
Functions of bone (6)
1. Structural support 2. Levers for movement 3. Protection of internal organ systems 4. Hematopoiesis 5. Mineral storage 6. Lipid storage
Surgical options vary by fracture type:
Air boots Casting Pins Plates and screws Combination of above ^
Epiphysis (long bone anatomy)
At each end of long bones Proximal, distal Compact bone → spongy bone (no cavity) Covered in articular cartilage
Metaphysis (long bone anatomy)
At ends of shaft - Compact bone → spongy bone (no cavity) - Contains epiphyseal plate (growth plate) → epiphyseal line (adults) - made of hyaline cartilage
Compound (open) fracture
Broken ends penetrate skin Infection can more easily set in
organic portion and inorganic portion
Bone matrix has an
Mineral storage (bone function)
Ca+2 → muscle contraction, blood clotting, cell signaling PO4-3 → ATP, nucleic acids, phospholipid
Central canal (Haversian canal) (osteon cylinder)
Carries blood vessels and nerves
Inner layer (of the periosteum)
Cellular layer containing: Osteoprogenitor cells Osteocytes Osteoblasts Osteoclasts
Irregular bones (bone classification)
Complex shapes Ex: vertebrae, certain skull bones (ethmoid, etc), bones of pelvis
Within trabeculae:
Concentric lamellae (circles of bone surrounding each other) Osteocytes in lacunae (cavity) Canaliculi (connecting lacunae) Scattered osteoblasts, osteoclasts (cells)
displaced vs. nondisplaced (fracture characterization)
Describes whether ends of bone are misaligned or aligned
Vitamin D is required
Enhances calcium absorption from GI tract
Outer layer (of the periosteum)
Fibrous layer Protects bone Anchors blood vessels and nerves to bone surface Attachment site for ligaments, tendons
intramembranous ossification produces
Flat bones of face Cranial bones (most) Clavicles
Flat bones (bone classification)
Flat, thin Surface area for skeletal muscle attachment Ex: cranium of skull, scapulae, sternum, ribs
Vitamin C is required
For collagen formation Lack of Vitamin C → rickets
Comminuted fracture
Fragmented, splintered
Epiphyseal plate
Growth plate, becomes epiphyseal line in adults - made of hyaline cartilage
Hematoma formation (fracture repair)
Immediate formation upon fracture Blood vessels broken Blood clot/s form
Pathological fracture
In bone weakened by disease (osteoporosis, cancer)
Chondrocytes (in fibrocartilage)
In lacunae Arranged in rows between the collagen bundles
Two types of ossification
Intramembranous ossification Endochondral ossification
Osteoclasts
Large, multinuclear cells with ruffled border Phagocytic - consume other bone cells Perform bone resorption
Short bones (bone classification)
Length ~ width Ex: bones of wrist and ankle, sesamoid bones along certain tendons, patella
Endosteum (long bone anatomy)
Lines medullary cavities Contains osteoprogenitor cells, osteoblasts, and osteoclasts (NO osteocytes)
endochondral ossification produces
Long bones Cranial bones at the base of skull
Chondrocytes (in hyaline cartilage)
Maintains cartilage matrix In lacunae (spaces holding cells)
Osteocytes
Mature bone cells Develop projections (like dendritic cells) Maintain bone matrix Detect mechanical stress → signal osteoblasts → make more matrix
Fibrocartilage anatomy
More fibrous looking, avascular, no innervation Dense bundles of collagen fibers provide increased strength and resilience chondroblasts chondrocytes fibroblasts fibrocytes perichondrium
At birth: (bone development)
Most cartilage is now bone Cartilage remains in skull, clavicles, epiphyseal plates
Through childhood: (bone development)
Most remaining cartilage becomes bone Some cartilage remains (epiphyseal plates)
anatomy of other bone types:
No medullary cavity (compact bone → spongy bone)
Trabeculae (of spongy bone)
Open lattice of rods and plates Covered in endosteum Provides for resistance to various stresses
Organic portion (of bone matrix)
Osteoid = collagen fibers + ground substance (proteoglycan + glycoproteins) + water "rebar"
Proteolytic enzymes
Produced by lysosomes Digest collagen fibers and proteoglycan Acid dissolves the hydroxyapatite → releases Ca+2 and PO4-3 into blood
Fibroblasts (in fibrocartilage)
Produces cartilage matrix Become encased, mature → becomes fibrocytes
Hematopoiesis (bone function)
Productions of blood cells Occurs in red bone marrow - stem cells divide and produce red and white blood cells
Concentric lamellae (compact bone)
Rings of bone within an osteon Surround central canal Each lamellae contains collagen fibers oriented in one direction Next lamellae contain fibers at 90 degrees to the last one Alternating pattern → strength, resilience (collagen fibers rebar of concrete)
Lack of exercise on bone health
Sedentary lifestyle → decreased bone strength Malnutrition → decrease bone strength Calcium + Vitamin D Vitamin D + Vitamin K Omega-3 fatty acids and inflammation Casting a fracture → decreased bone strength Astronauts → decreased bone strength
osteoporosis risk factors
Sex (female > male) Age (>50 years) Loss of estrogen after menopause Poor diet (all the way through life!) Lack of exercise Family history (but not inevitable! Take good care of bones!)
Diaphysis (long bone anatomy)
Shaft Provides primary weight support Cortical bone → spongy bone → medullary cavity
Diploe
Spongy bone between inner and outer layers of cranial bones
Stress fracture
Thin break From physical activity → repetitive loading (ex: running)
fills space between trabeculae
When present, bone marrow extending from medullary cavity
parathyroid hormone (bone health)
absorption of calcium from GI tract - stimulates osteoclasts
Hyaline cartilage
appearance is "glassy" / "translucent" Serves as first template of a skeleton in fetus Attaches ribs to sternum Covers ends of some bones (articular)
Levers for movement (bone function)
attachment site for skeletal muscle
Endochondral ossification
bone develops by replacing hyaline cartilage begins in utero, into adolescence
Intramembranous ossification
bone develops directly from early mesenchymal connective tissue - begins in utero, into adolescence
As the fetus grows
bone forms through ossification
Osteoid
bone matrix; specialized ECM secreted by osteoblasts
osteoporosis cause
bone resorption > bone formation Lose too much bone Make too little bone
Skeletal system =
bones cartilage ligaments tendons joints
Primary bone
brand new, young bone
fracture
breakage of bone Results from application of unusual stresses or sudden impact
Simple (closed) fracture
broken ends do not penetrate skin
Hydroxyapatite crystals deposited in matrix
calcification, mineralization [Ca+2] and [PO4 -3] reached threshold → precipitation occurs Hydroxyapatite → deposits around collagen fibers
Malnutrition: decreased bone strength
calcium + vitamin D vitamin D + vitamin K Omega-3 fatty acids (reduce inflammation)
Spongy bone
cancellous / trabecular bone 20% of total bone internal to compact/cortical bone porous - space in and around twists and turns
Medullary cavity
cavity within the shaft of the long bones filled with bone marrow - red marrow in children - yellow marrow in adults
growth hormone (bone health)
continuing growth of bones throughout childhood adolescence
Compact bone
cortical bone 80% of total bone exterior regions of bone smooth, very solid
Perichondrium
covering of dense, irregular CT over cartilage (exception: articular cartilage)
Hydroxyapatite
crystals deposited in and around the collagen fibers in the osteoid, harden that material to make bone - calcium phosphate and calcium hydroxide -
material of tendons and ligaments -
dense, regular connective proper
Oblique (fracture characterization)
diagonal fracture
Structural support (bone function)
framework for the human form
Hyaline cartilage anatomy
glassy, avascular, little innervation; perichondrium chondroblasts chondrocytes
Organic/Inorganic portions must be
dynamically optimized - balancing act, making the foundation - Loss of proteins, abnormal → brittle bones - Insufficient calcium (for hydroxyapatite) → soft bones
Circumferential lamellae (compact bone)
extend entire circumference of the bone external; internal
procallus
fibrocartilaginous (soft) callus actively growing connective tissue
Spiral (fracture characterization)
fracture around, in 3 dimensions
Transverse (fracture characterization)
fracture in the transverse plane
Linear (fracture characterization)
fracture within bone; parallel to diaphysis
Hormones (contributing to bone balance)
growth hormone thyroxine (thyroid) sex hormones calcitriol calcitonin parathyroid hormone
Bony callus (fracture repair)
hard develops 1 week → 12-16 weeks after fracture - Osteoprogenitor cells (immature bone cells) adjacent to developing soft callus divide → osteoblasts produced - Osteoblasts produce trabeculae of primary bone - Trabeculae infiltrate and replace soft callus Soft callus → hard callus
Calcitonin (bone health)
helps stimulate osteoblasts - stimulate body to take up calcium
Osteoprogenitor cells
immature bone cells, bone stem cells become osteoblasts
osteocytes
in spaces between concentric lamellae Maintain bone matrix
Lipid storage (bone function)
in yellow bone marrow
Greenstick fracture (fracture characterization)
incomplete fracture, don't break through both side of the bone (common in young children)
lamellae=
layer
Classification of bones
long bones short bones flat bones irregular bones
Fibrocytes (in fibrocartilage)
maintains matrix
Spongy bone anatomy
no osteons contains trabeculae
Bone:
primary organ of the skeletal system - dynamic tissue - develops in fetus > grows in childhood > constantly remodeling in adulthood - two types: compact; spongy
Chondroblasts (in fibrocartilage)
produce cartilage matrix
Osteoclasts release
proteolytic enzymes into bone matrix
internal circumferential lamellae
rings immediately external to the endosteum
external circumferential lamellae
rings immediately internal to periosteum
Types of bone fractures
simple compound comminuted stress pathological
During fetal development
skeletal system begins with cartilage template
Fibrocartilaginous callous formation (fracture repair)
soft develops 4 days - 3 weeks after fracture - Newly formed capillaries infiltrate hematoma - Trigger formation of procallous - Fibroblasts produce collagen fibers - Chondroblasts form dense, regular CT
Cartilage
softer, supporting CT with semisolid matrix - mature form is avascular - two types: hyaline; fibrocartilage
Lacunae (compact bone)
spaces that house osteocytes
material of cartilage
supporting CT (semisolid matrix; softer)
material of bone
supporting CT (solid matrix; harder)
Remodeling (fracture repair)
takes time 4 weeks - 5 years after fracture - Fibroblasts and fibrocytes involved, osteoclasts remove excess bone to restore normal anatomy - Osteoclasts remove excess bone material both inside and outside surface of bone - Primary bone replaced by compact bone - Some compact bone thickening will persist; protective against future fracture in the same area
low calcium levels in blood (low Ca+2)
triggers increased amounts of bone resorption; body draws Ca+ from the bones
osteoporosis primarily affects
wrists, vertebrae, metaphysis of femur