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 Y
calcitonin gene-related peptidevasoactive intestinal peptide
substance 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