Bone Modeling/Remodeling
- Bone modeling: bone formed by osteoblasts w/o prior bone resorption. Happens during growth. Changes bone size and shape
- Bone remodeling: occurs when bone is first resorbed by osteoclasts and then formed in same location by osteoblasts. happens throughout life
- Goal: achieve strength for loading and lightness for mobility
Extracellular Bone Matrix
- Organic components (from osteoblasts): ground substance (glycoproteins and negatively charged trap water), collagen fibers (provide flexibility and framework for deposition of calcium)
- Inorganic components: Water (25% of matrix), hydroxyapatite
- Collagen provides flexibility and minerals provide firmness
Spongy Bone
Organization:irregular lattice of thin plates called trabecullae, osteocytes housed in lacunae
location: epiphyses of long bones and surrounding marrow cavities and flat short irregular bones
functions: to withstand forces in many directions and lighten skeleton and contain red marrow
Compact bone
- Organization: solid network of bone organized in concentric ring structures called osteons
- Location: external layer of all bones, diaphysis of long bones
- Function: gives long bones ability to withstand forces along longitudinal axis
Osteon
- Functional unit of compact bone
- has concentric lamellae, blood vessels, and osteocytes in lacunae and canaliculi
Growth at Epiphyseal Plate
Growth happens first through Interstitial Growth to make cartilage and then the cartilage is replaced by bone through Endochondral Ossification (secondary).
- osteoclasts break down calcified cartiliage
- osteoblasts lay down spongy bone
- chondrocytes form more cartilage at proliferating cartilage region
Appositional Growth
- growth in width
- periosteal osteogenic cells differentiate into osteoblasts
- osteoblasts build bone on outer surface and endosteal osteoclassts increase the diameter of the marrow cavity
- bone diameter and cortical width increase
Calcitonin
- Stimulus: high blood calcium
- Source: thyroid gland
- Target Tissue: bone, kidney, intestine
- Actions (goal is to decrease blood Ca): inhibits osteoclast activity, increases excretion of calcium at kidney, inhibits absorption of Ca at intestine
Parathyroid Hormone
- Stimulus: Low blood Calcium
- Source: Parathyroid gland
- Target Tissues: bone, kidney, intestine
- Actions (goal is to increase blood calcium): stimulates osteoclast activity, decreases excretion of calcium at kidney, stimulates intestinal absorption of calcium and promotes calcitriol acttion
Vitamin D pathway
skin (vitamin D precursor 7-dehydrocholesterol) => + UV light=> skin (vitamin D3 Cholecalciferol) or Intestine (dietary vitamin D3) => blood => liver (25-hydroxy-cholecalciferol (Calcidiol)) => blood=> kidney (1,25 dihydroxy-cholecalciferol)
-Absorption at kidney is stimulated by PTH and Low Blood Calcium
Calcitriol (active Vitamin D)
- stimulates osteoclast activity (increases bone resorption)
- Decreases calcium excretion at the kidney
- Increases calcium absorption at the intestine
Role of Exercise in bone mass
Goal: reach fracture threshold later in life
- exercise early in life=>increase peak bone mass
- Exercise later in life=> prevent bone loss
- other benefits=> fall prevention from improved strength and balance
Skeletal Disorders associated with GH
Pituitary Dwarfism: low growth hormone=>short stature
Pituitary Giantism: hypersecretion of growth hormone during childhood => tall stature
Acromegaly: Hypersecretion of growth hormone after puberty=> appositional growth in skull, hands, and feet
8 Bones of the cranium
- Frontal
- Parietal (2)
- Occipital
- Temporal (2): styloid process anterior to mastoid process
- Sphenoid: greater wings and lesser wings and optic foramen
- Ethmoid: Crista Galli, Cribriform Plate, Olfactory Foramina, perpendicular plate
Cranial Sutures
- Sagital suture: between parietal bones
- Coronal suture: between parietal+frontal
- Lambdoidal suture: between parietal+occipital
- Squamousal suture: Between temporal + parietal and everything
14 Facial Bones
- Zygomatic bones (2)
- Maxilllae (2)
- Mandible
- Lacrimal (2)
- Nasal bones (2)
- Vomer
- Inferior Nasal Conchae (2)
- Palatine bones (2)
Articulations of the ribs and the vertebrae
-Superior (demi)facet of vertebrae #n with head of rib #n
-tubercle of rib #n with facet for tubercle #n
-inferior demifacet #n with head of rib #n+1
T1: superior facet, not demifacet
T2-T8: superior and inferior demifacets
T10: Superior facet
T11 and T12: facet for head of rib but no facet for tubercles
Elbow Joint
- Coronoid process of ulna articulates with coronoid fossa of humerus
- Radius head articulates with Capitulum of humerus
- Olecranon process of ulna articulates with olecranon fossa of humerus
- Trochlea notch of ulna with trochlea of humerus
Hip
-Head of femur with acetabulum of coxal bone (os coxa)
Knee Joint
- -lateral condyle of femure with fibula
- Medial condyle of femure with tibia
the 3 functional classifications of articulations
- Synarthroses: immovable joints include sutures
- Amphiarthroses: slightly movable joints include intervertebral joints, the tibiofibular joint
- Diarthroses: freely moveable joints include most joints of body
Synovial Joint
- Synovial cavity: small space between two articulating bones
- articular cartillage: hyaline cartilage covering both ends of bones
- articular capsule: encloses the synovial cavity include fibrous and synovial membranes
- synovial fluid secreted by synovial membrane
4 cell types of bone
- Osteogenic cell: develops into an osteoblast. Stem cells formed from mesenchyme
- Osteoblast: forms bone matrix, synthesize organic components of matrix (immature cell)
- Osteocyte: maintains bone tissue (sense bone microdamage) mature
- Osteoclast: functions in resorption, the breakdown of bone matrix; derived from myloid stem cells (not from osteogenic cells)
