Functional Anatomy of the Skeletal System Flashcards
Cartilage
- The fetal precursor tissue in the development of many bones
- Supports non-skeletal structures (e.g. ear, larynx, tracheobronchial tree)
- Chondrocytes aggregate in lacunae (openings), forming isogenous groups
Properties of Cartilage
- Avascular
- Permeable (conducts nutrients/water)
- Flexible, but weight bearing (resistance to compression)
- Elasticity & resiliency
- Resistance to shear forces
- Slippery (low friction at articular joints)
- Poor regenerative capacity
Types of Cartilage
- Differ only in the fiber types*
1. Hyaline cartilages- Provide support, flexibility, & resilience
- Most abundant type
- Elastic cartilages
- Similar to hyaline, but have elastic fibers
- Fibrocartilages
- Collagen fibers-good tensile strength
Hyaline Cartilages
Matrix (amorphous & glassy) - hyaluronic acid - chondroitin sulfate - keratin sulfate - H20 (60-70%) Fibers (*collagenous*) - Invisible d/t refractive matrix index
NOTE: May become calcified
Hyaline Cartilage Locations
- Intercostals (connect ribs to the sternum)
- Wall of trachea & bronchi
- Articular cartilage of bone
- Epiphyseal plate
- Fetal axial skeleton
Fibrocartilage
Matrix - Hyaluronic acid - Chondroitin sulfate - Keratin sulfate - Water Fibers - *Dense collagenous* bundles Properties - Resistance to compression & shear forces
Fibrocartilage Locations
- Partially moveable joints*
- Intervertebral discs
- Pubic symphysis
- Meniscus of knee joint
- Attach tendons to bone
Elastic Cartilage
Matrix - hyaluronic acid - chondroitin sulfate - keratin sulfate - water Fibers - elastic (*elastin*) Properties - resiliency - pliability
Elastic Cartilage Locations
- External ear
- Walls of external auditory canal & eustachian tubes
- Epiglottis & larynx
- Bridge of the nose
Growth of Cartilage
Appositional Growth:
- Peripheral* mitosis & differentiation of fibroblasts (upward growth towards the perichondrium)
- Multiplication & growth
- Occurs in mature cartilage
Interstitial Growth:
Mitosis of chondrocytes & deposition of new matrix (upward & inward growth)
- Occurs in the stroma
- Occurs in young cartilages
Bone
Living, vascular form of connective tissue
- 206 bones in the human skeleton
Functions:
- support/shape
- protection
- movement
- mineral (Ca, fat, marrow) & growth factor storage
- blood cell formation
- triglyceride (fat) storage
Bone Classification: Location
2 groups, based on location - Axial skeleton (brown) `skull, vertebral column, ribcage - Appendicular skeleton (yellow) `upper & lower limbs
Bone Classification: Shapes
- Long bone--longer than wide ` ex. humerus - Short bones-- ` cube-shaped (wrist/ankle-talus) ` sesamoid bones (in tendons, e.g. patella) - Flat bones--thin, flat, slightly curved ` ex. sternum, skull - Irregular bones--complicated shapes ` ex. vertebra
Bone Classification: Texture
Compact bone:
- Dense
- Usually limited to the cortices of mature bones (outer surfaces of bone)
Cancellous:
- Lattice of bone spicules
- Occurs in the ends of long bones
- Fills flat & irregular bones
Periosteum
- Outer fibrous layer
- Inner osteogenic layer
` osteoblasts (bone-forming cells)
` osteoclasts (bone-destroying cells)
` osteogenic cells (stem cells) - Nerve fibers, nutrient blood vessels, & lymphatic vessels enter bone via the nutrient foramina
- Secured to underlying bone by Sharpey’s fibers (perforating fibers)
Endosteum
- Delicate membrane on internal surfaces of bone
- Contains osteoblasts & osteoclasts
Location of Hematopoietic Tissue
Hematopoietic Tissue = Red Marrow
- Trabecular cavities of the heads of the femur & humerus
- Trabecular cavities of the dipole of flat bones
Red bone marrow of newborn infants:
- Medullary cavities & all spaces in spongy bone
Blood Supply of a Long Bone
Diaphysial artery (1 or 2)
- Enter shaft obliquely through nutrient foramina -> lead to nutrient canals
- Entrance is characteristically away form the dominant growing epiphysis (e.g. growing end in leg is at knee, enter & point toward hip)
Metaphysial artery
Epiphysial artery
NOTE: epiphyseal & metaphysial arteries join the diaphysial arteries near the epiphysis
Nerve Supply of Bones
- Autonomic & sensory supply
- Most numerous in the articular extremities
- Osteoblast possess receptors for neuropeptides found in nerves
neuropeptide Ycalcitonin gene-related peptidevasoactive intestinal peptidesubstance P
Microstructure of Bones
Components:
- mineralized extracellular matrix
- specialized cells
- components of the periosteum, endosteum, & marrow
Bone Matrix
- Consists of ground substance w/ numerous collagen fibers
- 10-20% of mass = water
- 60-70% of mass = inorganic salts & mineral salts (microcrystalline calcium & phosphate hydroxides -> hydroxyapatite)
- Proportions vary w/ age, location & metabolic status
Bone Cells
Osteogenic (osteoprogenitor) cells
= Stem cells in periosteum & endosteum that give rise to osteoblasts
Osteoblasts
= matrix synthesizing cell responsible for bone growth
Osteocytes
= mature bone cells
Osteoclasts
= cells that break down (resorb) bone matrix
Microstructure of Bone: Compact Bone
Haversian system, or osteon = structural unit
- Lamellae
weight-bearing
column-like matrix tubes
- Central (Haversian) canal–contains blood vessels & nerves
- Perforating (Volkmann’s) canals
at right angles to the central canal
connects blood vessels & nerves of the periosteum & central canal
- Lacunae–small cavities that contain osteocytes
- Canaliculi–hairlike canals connecting lacunae to each other & the central canal
Microstructure: Spongy Bone
Trabeculae
- Align along lines of stress
- No osteons
- Contain irregularly arranged lamellae, osteocytes, & canaliculi
- Capillaries in endosteum supply nutrients
Types of Ossification
(1) Intramembranous
- membrane bone develops from fibrous membrane
- forms flat bones (e.g. clavicles & cranial bones)
(2) Endochondral
- cartilage (endochondral) bone forms by replacing hyaline cartilage
- forms most of the rest of the skeleton
Intramembranous Ossification Process
- Mesenchymal cells cluster & differentiate into osteoblasts -> form ossification center in fibrous connective tissue membranes
- Osteoblasts begin secreting osteoid -> calcification within days -> trapped osteoblasts become osteocytes
- Accumulating osteoid deposited b/t embryonic blood vessels randomly -> network of trabeculae (= woven bone); vascular mesenchyme condenses on external woven bone -> periosteum
- Trabeculae below periosteum thicken & are replaced w/ mature lamellar bone -> compact bone plates; spongy bone (dipole), become red marrow
Endochondral Ossification
- Uses hyaline cartilage models
- Requires breakdown of hyaline cartilage prior to ossification
Endochondral Ossification Process
- Bone collar forms around hyaline cartilage model
- Cartilage in the center of the diaphysis calcifies & develops cavities
- Periosteal bud inavades the internal cavities & spongy bone begins forming
- Diaphysis elongates & a medullary cavity forms; secondary ossification centers appear in the epiphyses
- Epiphyses ossify, then hyaline cartilage remains only in the epiphyseal plates & articular cartilages
Post-natal Bone Growth
Interstitial Growth:
- increases length of long bones
Appositional Growth:
- increases thickness & remodeling of all bones by osteoblasts & osteoclasts on bone surfaces
Epiphyseal Functional Zones
- Proliferation (growth)
- cartilage cells undergo mitosis
- Hypertrophic
- older cartilage cells enlarge
- Calcification
- matrix becomes calcified
- cartilage cells die
- matrix begins deteriorating
- Ossification (osteogenic)
- new bone forms
Control of Bone Remodeling
- Hormonal mechanisms that maintain calcium homeostasis in the blood
- Mechanical & gravitational forces
Parathyroid Hormone Control of Blood Ca2+
Primarily control of blood Ca2+ levels
Decreased blood Ca2+ levels -> parathyroid glands release of PTH -> PTH stimulates osteoclasts to degrade bone matrix & release Ca2+ -> increased blood Ca2+ levels
Calcitonin Control of Blood Ca2+
Less control than PTH
Increased blood Ca2+ -> parafollicular cells of thyroid release calcitonin -> osteoblasts deposit calcium salts -> decrease blood Ca2+ levels
Leptin Control of Bone Density
Influences bone density by inhibiting osteoblasts
Blood Supply of a Long Bone
Diaphysial artery (1 or 2)
- Enter shaft obliquely through nutrient foramina -> lead to nutrient canals
- Entrance is characteristically away form the dominant growing epiphysis
Metaphysial artery
Epiphysial artery
NOTE: epiphyseal & metaphysial arteries join the diaphysial arteries near the epiphysis
Blood Supply of a Long Bone
Diaphysial artery (1 or 2)
- Enter shaft obliquely through nutrient foramina -> lead to nutrient canals
- Entrance is characteristically away form the dominant growing epiphysis
Metaphysial artery
Epiphysial artery
NOTE: epiphyseal & metaphysial arteries join the diaphysial arteries near the epiphysis
Nerve Supply of Bones
- Autonomic & sensory supply
- Most numerous in the articular extremities
- Osteoblast possess receptors for neuropeptides found in nerves
neuropeptide Ycalcitonin gene-related peptidevasoactive intestinal peptidesubstance P
Nerve Supply of Bones
- Autonomic & sensory supply
- Most numerous in the articular extremities
- Osteoblast possess receptors for neuropeptides found in nerves
neuropeptide Ycalcitonin gene-related peptidevasoactive intestinal peptidesubstance P
Microstructure of Bones
Components:
- mineralized extracellular matrix
- specialized cells
- components of the periosteum, endosteum, & marrow
Microstructure of Bones
Components:
- mineralized extracellular matrix
- specialized cells
- components of the periosteum, endosteum, & marrow
Bone Matrix
- Consists of ground substance w/ numerous collagen fibers
- 10-20% of mass = water
- 60-70% of mass = inorganic salts & mineral salts (microcrystalline calcium & phosphate hydroxides -> hydroxyapatite)
- Proportions vary w/ age, location & metabolic status
Bone Matrix
- Consists of ground substance w/ numerous collagen fibers
- 10-20% of mass = water
- 60-70% of mass = inorganic salts & mineral salts (microcrystalline calcium & phosphate hydroxides -> hydroxyapatite)
- Proportions vary w/ age, location & metabolic status
Bone Cells
Osteogenic (osteoprogenitor) cells
= Stem cells in periosteum & endosteum that give rise to osteoblasts
Osteoblasts
= bone forming cells
Bone Cells
Osteogenic (osteoprogenitor) cells
= Stem cells in periosteum & endosteum that give rise to osteoblasts
Osteoblasts
= matrix synthesizing cell responsible for bone growth
Osteocytes
= mature bone cells
Osteoclasts
= cells that break down (resorb) bone matrix
Microstructure of Bone: Compact Bone
Haversian system, or osteon = structural unit
- Lamellae
weight-bearing
column-like matrix tubes
- Central (Haversian) canal–contains blood vessels & nerves
- Perforating (Volkmann’s) canals
at right angles to the central canal
connects blood vessels & nerves of the periosteum & central canal
- Lacunae–small cavities that contain osteocytes
- Canaliculi–hairlike canals connecting lacunae to each other & the central canal
Microstructure: Spongy Bone
Trabeculae
- Align along lines of stress
- No osteons
- Contain irregularly arranged lamellae, osteocytes, & canaliculi
- Capillaries in endosteum supply nutrients
Types of Ossification
(1) Intramembranous
- membrane bone develops from fibrous membrane
- forms flat bones (e.g. clavicles & cranial bones)
(2) Endochondral
- cartilage (endochondral) bone forms by replacing hyaline cartilage
- forms most of the rest of the skeleton
Ossification Process
- Mesenchymal cells cluster & differentiate into osteoblasts -> form ossification center in fibrous connective tissue membranes
- Osteoblasts begin secreting osteoid -> calcification within days -> trapped osteoblasts become osteocytes
- Accumulating osteoid deposited b/t embryonic blood vessels randomly -> network of trabeculae (= woven bone); vascular mesenchyme condenses on external woven bone -> periosteum
- Trabeculae below periosteum thicken & are replaced w/ mature lamellar bone -> compact bone plates; spongy bone (dipole), become red marrow
Endochondral Ossification
- Uses hyaline cartilage models
- Requires breakdown of hyaline cartilage prior to ossification
Endochondral Ossification Process
- Bone collar forms around hyaline cartilage model
- Cartilage in the center of the diaphysis calcifies & develops cavities
- Periosteal bud inavades the internal cavities & spongy bone begins forming
- Diaphysis elongates & a medullary cavity forms; secondary ossification centers appear in the epiphyses
- Epiphyses ossify, then hyaline cartilage remains only in the epiphyseal plates & articular cartilages
Post-natal Bone Growth
Interstitial Growth:
- increases length of long bones
Appositional Growth:
- increases thickness & remodeling of all bones by osteoblasts & osteoclasts on bone surfaces
Epiphyseal Functional Zones
- Proliferation (growth)
- cartilage cells undergo mitosis
- Hypertrophic
- older cartilage cells enlarge
- Calcification
- matrix becomes calcified
- cartilage cells die
- matrix begins deteriorating
- Ossification (osteogenic)
- new bone forms
Control of Bone Remodeling
- Hormonal mechanisms that maintain calcium homeostasis in the blood
- Mechanical & gravitational forces
Parathyroid Hormone Control of Blood Ca2+
Primarily control of blood Ca2+ levels
Decreased blood Ca2+ levels -> parathyroid glands release of PTH -> PTH stimulates osteoclasts to degrade bone matrix & release Ca2+ -> increased blood Ca2+ levels
Calcitonin Control of Blood Ca2+
Less control than PTH
Increased blood Ca2+ -> parafollicular cells of thyroid release calcitonin -> osteoblasts deposit calcium salts -> decrease blood Ca2+ levels
Leptin Control of Bone Density
Influences bone density by inhibiting osteoblasts
Bone Response to Mechanical Stress
Wolff’s Law–bone grows or remodels in response to forces or demands placed upon it
Supporting observations:
- R or L handedness -> thicker/stronger bones in one upper limb
- Curved bones are thickest where they are most likely to buckle
- Trabeculae form along lines of stress
- Large, bony projection occur where heavy, active muscles attach
Bone Response to Mechanical Stress
Wolff’s Law–bone grows or remodels in response to forces or demands placed upon it
Supporting observations:
- R or L handedness -> thicker/stronger bones in one upper limb
- Curved bones are thickest where they are most likely to buckle
- Trabeculae form along lines of stress
- Large, bony projection occur where heavy, active muscles attach
Joints
Region of the skeleton where 2 or more bones meet & articulate
Functional Classification of Joints
Based on the amount of movement allowed by the joint
- Synarthroses–immovable
- Amphiarthroses–slightly movable
- Diarthroses–freely movable
Structural Classification of Joints
Based on material binding bones together & whether or not a joint cavity is present
- Fibrous
- Cartilaginous
- Synovial
Fibrous Joints
- bones joined by dense fibrous connective tissue
- no joint cavity
- most are synarthrotic (immovable)
Types:
- Sutures
- Syndesmoses
- Gomphoses
Fibrous Joints: Sutures
Joint held together w/ very short, interconnecting fibers, & bone edges interlock
found only in the skull
Fibrous Joints: Syndesmosis
Joint held together by a ligament
- fibrous tissue can vary in length, but is longer than sutures
*Ex. fibula & tibia connection
Fibrous Joints: Gomphosis
“Peg in socket”
- *Ex. periodontal ligament
Cartilaginous Joint
- bones united by cartilage
- no joint cavity
Types:
- Synchondroses
- Symphyses
Cartilaginous Joint: Synchondroses
A bar or plate of hyaline cartilage that unites the bones
- Epiphyseal plate (temporary hyaline cartilage joint)
- Joints b/t sternum (manubrium) & 1st rib
Cartilaginous Joint: Symphyses
Hyaline cartilage covers the articulating surfaces & is fused to an intervening pad of fibrocartilage
- ex. intervertebral discs & pubic symphysis
Synovial Joints
Joints w/ maximum amount of movement
- all ar diarthrotic
- includes all limb joints & most joints of the body
Synovial Joints: Distinguishing Features
- Articular cartilage–hyaline cartilage
- Joint (synovial) cavity–small potential space
- Articular (joint) capsule
Outer fibrous capsule = dense irregular CTInner synovial membrane = loose CT - Synovial fluid
Viscous filtrate (plasma + hyaluronic acid)Lubricates & nourishes articular cartilage
Types of Synovial Joints
- Plane (ex. joint b/t intercarpal bones)
- Hinge (ex. elbow joint)
- Pivot (ex. b/t atlas & axis–C1-2)
- Bicondylar (ex. knee)
- Ellipsoid (ex. radiocarpal joint)
- Saddle (ex. 1st carpometacarpal joint-thumb)
- Ball & Socket (ex. shoulder, hip)
Bursae
= Synovial joint
- friction-reducing structure
- flattened, fibrous sacs lined w/ synovial membranes (extension outside joint cavity)
- contain synovial fluid
- commonly act as “ball bearings” where ligaments, muscles, skin, tendons, or bones rub together (ex. b/t scapula & humerus)
Tendon Sheath
= Synovial joint (extension of a synovial membrane outside the joint cavity
- friction-reducing structure
- elongated bursa that wraps completely around a tendon
