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