Skeletal System and Bones Flashcards
Axial Skeleton
bones of:
- head
- neck
- trunk (inc. spine and ribcage)
Appendicular Skeleton
bones of limbs (inc. pectoral and pelvic girdle)
What are bones made of?
= form of connective tissue
- 35% organic components (eg: collagen)
- 65% inorganic hydroxyapatites (mineral salts such as calcium phosphate –> enables bones to be opaque on X-rays)
Minerals = help bones resist compression Collagen = resist tension
all bones are derived from MESENCHYME via 2 processes (intramembranous and endochondral ossification)
Gross Bone Anatomy
Consists of compact bone sandwiching spongy bone
Compact bone: dense bone that forms the outer shell of all bone
- surrounds spongy bone
- has hollow pillars of bone matrix that contain nerves and blood vessels
Spongy Trabecular Bone: trabeculae that are aligned in specific ways to assist with weight bearing
- trabeculae form lines of tensile stress that intersect with lines of compressive stress
- filled with red or yellow bone marrow in the medullary cavity
Bone Shape Classification
Long Bones:
- longer than they are wide
- bear lots of weight (eg: femur, humerus)
Short Bones:
- similar width and length (cube-shaped)
- for stability and support with little movement (eg: carpal bones)
- sesamoid bones = special type that forms in a tendon
Flat bones:
- thin, flattened, usually slightly curved
- protect vital organs and provide surfaces for muscle attachments (eg: sternum, skull bones)
Irregular Bones: (eg: vertebrae)
Gross Anatomy of a Long Bone
Articular Cartilage: thin layer of hyaline cartilage that reduces friction and acts as a shock absorber
Proximal Epiphysis (and Distal): filled with spongy bone and red bone marrow
Metaphysis: where diaphysis meets epiphysis
Diaphysis: hollow, tubular shaft b/w proximal and distal ends containing the medullary cavity and yellow bone marrow
Endosteum: thin membrane lining medullary cavity, internal bone surfaces, trabeculae and canals of compact bone
Medullary Cavity: lined by endosteum, contains yellow bone marrow and blood vessels
Periosteum: contains blood vessels, nerves and lymphatic vessels that nourish compact bone
Nutrient artery: enters through foramen and branches off into capillaries to supply bone
Vascular Supply of a Bone
bone tissue and periosteum = have rich blood supply
- Periosteal Arteries:
- supply periosteum and outer compact bone
- enter through many small canals
- Large Nutrient Artery:
- enters via nutrient foramen at diaphysis centre
- enters medullary cavity and courses towards epiphysis
- Epiphyseal and Metaphyseal Arteries:
- supply ends of long bone
Types of Cells in Bone Tissue
Osteoblasts = bone building cells
- synthesise and secrete collagen fibres & organic compounds –> builds ECM of bone
- initiates calcification
Osteoclasts = Bone ECM breaking cells
- release lysosomal enzymes and acids to digest protein and mineral components of the ECM
Intramembranous Ossification
- directly from mesenchyme (mesenchymal cells –> osteoblasts)
- mesenchymal models of bone form during the embryonic period and direct ossification occurs during fetal period
- eg: flat skull bone, facial bones, mandibles, hardening of fontanelles (holes in skull)
- Development of Ossification Centre:
- osteoblasts secrete organic ECM - Calcification:
- calcium and other mineral salts are deposited and the ECM calcifices - Formation of Trabeculae:
- ECM develops –> trabeculae that fuse to form spongy bone - Development of the Periosteum:
- mesenchyme at periphery of bone develops –> periosteum
Endochondral Ossification
- from cartilage models of bones formed from mesenchyme during fetal period
- later, bones replace cartilage
- Development of Cartilage
- mesenchymal cells develop –> chondroblasts which form the cartilage model - Growth of the Cartilage Model
- growth occurs by chondrocyte cell division - Development of the Primary Ossification Centre
- bone tissue replaces cartilage in the middle - Development of Medullary Cavity
- bone breakdown by osteoclasts forms medullary cavity - Development of Secondary Ossification Centres:
- occurs in the proximal and distal epiphyses - Formation of Articular Cartilage and Epiphyseal Plate
- both consist of hyaline cartilage
Bone Growth from Infancy to Adolescence
Occurs longitudinally and appositionally (width) until ~25 years of age, after which only appositionally
Epiphyseal plates: begin as cartilage that allow bone to grow in length; ossifies after length is achieved
- Longitudinal Bone Growth: Interstitial growth of cartilage on epiphyseal side of epiphyseal plate
- replacement of cartilage on diaphyseal side –> bone via endochondral ossification occurs
- allows thickness of epiphyseal plate to remain constant while bone grows on diaphyseal side
- Epiphyseal plate closes at 18 yo in F and 21 yo in M to become the epiphyseal line - Appositional Bone Growth
- growth in thickness
- new bone deposited on outer surface and old bone lining of medullary cavity is destroyed
- therefore, medullary cavity enlarges as bone width increases
Bone Remodelling
Combination of bone deposit (osteoblasts) and bone reabsorption (osteoclasts)
- weight bearing exercise can stimulate bone remodeling –> prevent osteoporosis
Factors affecting Remodelling and Growth:
1. Vitamins and minerals (increased vit. D increases Ca absorption –> Ca hardens ECM)
- Exercise: weigh-bearing exercise stimulates osteoblasts
- Hormones: oestrogen and testosterone stimulate osteoblasts and osteoclasts
- decreased oestrogen after menopause means de-mineralisation of bones begins earlier in F
