Two main groups of skeleton?
Axis and Appendicular
Shape of bones
Long, short, flat, ireggular
Long bones
longer than they are wide. Ex: humerus
Example of a flat bone
sternum
Example of an irregular bone
vertebra
Example of a short bone
talus
Components of skeletal system?
Bone, Cartilage, Tendons, and Ligaments
Three types of cartilage?
Hyaline, Fibrocartilage, Elastic
To support, protect, move, store, and blood cell production
Functions of the skeletal system
What does the skeletal system store?
Ca and P stored and released as needed. Adipose tissue stored in marrow cavities
Parts of a long bone
Proximal epiphysis, Diaphysis, Distal epiphysis, Periosteum, Endosteum
Diaphysis?
Compact bone collar surrounds medullary (marrow) cavity.
In adults, what does the medullary cavity contain?
fat (yellow marrow)
Epiphyses
Expanded ends, spongy bone interior, Epiphyseal line, Articular line
Epiphyseal line?
remnant of growth plate
Articular (hyaline) cartilage
on joint surfaces. Doesn't ossify and persists through life
Periosteum
Outer fibrous layer, Osteoblasts, Osteoclasts, Osteogenic cells, Nerve fibers, nutrient blood vessels
How is Periosteum secured to underlying bone?
Sharpey's fiber (collagen)
Delicate membrane on internal surfaces of bone, contains osteoblasts, osteclasts, and osteogenic cells
Endosteum
Structure of short, flat, and irregular bones
Periosteum, Endosteum, diploe, trabeculae
Diploe
Spongy bone that is in flat bones
Bone forming through ossification/osteogenesis. Collagen is produced by ER and golgi.
Osteoblasts
Ossification
Formation of bone by osteoblasts. Osteoblasts communicate by gap junctions. Cells surround themselves by matrix
Location of Hematopoietic Tissue (Red Marrow) Blood Formation for adults?
Trabecular cavities of the heads of the femur and humerus and trabecular cavities of the diploe of flat bones
Location of Hematopoietic Tissue (Red Marrow) Blood Formation for newborns?
Medullary cavity and all spaces in spongy bone
Osteocytes
Mature bone cells. Nutrients diffuse through tiny amount of liquid surrounding cell and filling lacunae and canaliculi. Then can transfer nutrients from one cell to the next through gap junctions
Spaces occupied by osteocytes
Lacunae
Canals occupied by osteocytes and connect lacunae to each other and the central canal
Canaliculi
Resportion of bone (bone destroying) with ruffled border.
Osteoclasts
How do osteoclasts destroy?
H ions pumped across the membrane, acid forms, eats away bone. Release enzymes that digest the bone. They are multinucleated and probably arise from fusion of a number of cells
Osteoclasts are derived from?
monocytes
Stem cells (Osteochondral Progenitor cells)
Become chrodroblasts/osteoblasts
Collagen fibers randomly oriented, formed during fetal development and during fracture repair
Woven Bone
Mature bone in sheets called lamellae. Fibers are oriented in one direction in each layer but in different directions in different layers for strength.
Lamellar bone
Remodeling
Removing old bone and adding new.
Woven bone is remodeled into?
Lamellar bone
Haversian system (osteon)
Bone structural unit
Part of a bone that is weight bearing, column like matrix tubes
Lamellae
Central (Haversian) canal
Contains blood vessels and nerves
At right angles to the central canal. Connects blood vessels and nerves of the periosteum and central canal
Perforating (Volkmann's) canal
Part of spongy bone, align along lines of stress, no osteons, irregulary arranged lamellae, osteocytes, and canaliculi
Trabeculae
Organic components of bone
Osteogenic cells, osteoblasts, osteoclasts,osteocytes, osteoid
Osteoid
35% mass of bone, ground substance (proteoglycans, glycoproteins), collagen fibers for strength and flexibility
Inorganic components of bone
Hydroxyapatites
65% of bone by mass, mainly calcium phosphate crystals, responsible for hardness and resistance to compression
Hydroxyapatites
Two patterns of bone formation during fetal development
Intramembrous ossification, Endochondral ossification. Both produce woven bone that is then remodeled. After remodeling, formation cannot be distinguished
Endochondral ossification
Takes place in cartilage. Begins at end of 4th week of development. Forms bones of the base of skull, part of the mandible, and most the remaining bones of the skeletal system. Some ossification begins at week 8 some doesn't begin until 18-20 years of age
Intramembrous ossification
Takes place in connective tissue membranes, forms many skull bones, mandible.
Osteogenesis (ossification)
bone tissue formation
Stages of Osteogenesis
Bone formation(begins in 8th week of development), Postnatal bone growth (until early adulthood), Bone remodeling and repair (lifelong)
Centers of ossification
Locations in membrane where ossification begins
Large membrane covered spaces between developing skull bones; unossified
Fontanels
Bone Growth
Growth in length occurs at the epiphyseal plate, involves formation of new cartilage by interstitial cartilage growth, appositional growth on the surface of the cartilage
Growth from within
Interstitial growth
Closure of epiphyseal plate
Epiphyseal plate is ossified becoming the epiphyseal line. Between 12 and 25 years of age
Appositional growth
Interstitial growth cannot occur because matrix is solid, occurs on old bone and/or on cartilage surface
Zones of epiphyseal plate
Resting cartilage, proliferation, hypertrophy, calcification, ossified bone
Zone of resting cartilage
Cartilage attaches to the epiphysis
Zone of proliferation
New cartilage is produced on the epiphyseal side of the plate as the chondrocytes divide and form stacks of cells.
Zone of hypertrophy
Chondrocytes mature and enlarge
Zone of calcification
Matrix is calcified and chondrocytes die
Ossified bone
The calcified cartilage on the diaphyseal side of the plate is replaced by bone
Growth in bone length
Chondrocyte replication and hypertrophy resulted in interstitial cartilage growth, interstitial cartilage growth increases the length of the bone, Ossification of calcified cartilage produces additional bone on the diaphyseal side of the epiphyseal plate,
How is growth of bone width produced
Appositional growth beneath the periosteum (eventually become endosteum)
How is Bone remodeling controlled?
Every week 5-7% of our bone mass is recycled. Hormonal mechanisms that maintain calcium homeostasis in the blood, mechanical and gravitational forces.
What hormones regulate bone growth?
Growth, Thyroid, testosterone, and estrogen hormones
Stimulates epiphyseal plate activity
Growth hormone
Thyroid hormone
modulates activity of growth hormone
Testosterone/estrogen (at puberty)
Promote adolescent growth spurts, end growth by inducing epiphyseal plate closure
Calcium is necessary for
Transmission of nerve impulses, muscle contraction, blood coagulation, secretion by glands and nerve cells, cell division
Increased Blood Ca2+ is controlled by which hormone
PTH (parathyroid hormone)
How does PTH increase blood Ca2+?
Low blood Ca2+ levels, then parathyroid glands release PTH, PTH stimulates osteoclasts to resorb bone matrix and release Ca2+, Ca2+ increase
How are decreased Ca2+ levels controlled
first high Ca2+ levels, parafollicular cells of thyroid release calcitonin, decrease osteoclast activity, blood Ca2+ levels decrease
How does a bone respond to mechanical stress?
Wolff's law
Wolff's law
A bone grows/remodels in response to demands/forces placed upon it.
Observations that support Wolff's law?
right/left handedness results in one bone being thicker/stronger, curved bones are thickest where they're most likely to buckle, trabeculae form along the lines of stress, and large, bony projections occur where heavy, active muscles attach
Fractures described by:
location, external appearance,nature of the break
Bone fractures are classified by either/or:
position, completeness, orientation, penetration
Position of bone fractures are either/or:
Nondisplaced (ends retain normal position), Displaced (ends out of normal alignment)
Completeness of bone fractures are either/or
Complete (broken all the way through), Incomplete (not broken all the way through)
Orientation of the break to the long axis of the bone in a fracture is either/or:
Linear (parallel to long axis of the bone), Transverse (perpendicular to long axis of the bone)
Penetration of the bone in a fracture is either/or:
Compound (open, bone ends penetrate the skin), Simple (closed, bone ends do not penetrate the skin)
Stages in healing a bone fracture
Hematoma, Fibrocartilagenous callus, Bony callus, Bone remodeling,
Hematoma
Torn blood vessels hemmorage, clot (hematoma) form, site becomes swollen, painful, inflammed
Phagocytic cells clear debris, osteoblasts begin forming spongy bone within 1 week, Fibroblasts secrete collagen fibers to connect bone ends
Fibrocartilagenous callus
New trabeculae form a bony (hard) callus, bony callus formation continues until firm union is formed in about 2 months
Bony callus
Bone remodeling
In response to mechanical stressors over several months, final structure resembles original
Two homeostatic imbalances
Osteomalacia and rickets; osteoporosis
Osteomalacia
Calcium salts not deposited, caused by vitamin D deficiency or insufficient dietary calcium
Rickets
A childhood disease, causes bowed legs and other bone deformities
Osteoporosis
Loss of bone mass, bone resorption. In spongy bone of spine and neck of femur become most susceptible to fracture.
What are the risk factors of Osteoporosis?
Lack of estrogen, calcium, Vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus
Treatment and Prevention of Osteoporosis?
Calcium, Vitamin D, and fluoride supplements, increase weight bearing exercise through life, hormone (estrogen) replacement therapy (HRT) slows bone loss
Drugs that increase bone mineral density
Fosamax, SERMs, Statins
Medication that decreases osteoclast activity number
Fosamax
Medication that mimics estrogen beneficial bone sparing properties without affecting the uterus or breasts
SERMS
Medication that lowers cholesterol
Statins
What age are almost all bones ossified by?
25
When does bone mass begin to decrease
4th decade
Rate of bone loss is determined by:
genetics and environmental factors