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4 types of bones
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Long bones, Short bones, Flat bones, Irregular Bones
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4 types of bones
Long bones, Short bones, Flat bones, Irregular Bones
Serve various needs & their size, shape & appearance will vary to meet those needs.
Compact bone
Dense & solid in appearance
Cancellous bone
Characterized by open space partially filled with needlelike structures
Parts of a long bone
Diaphysis, epiphysis, articular cartilage, periosteum, medullary (marrow) cavity, endosteum
Main shaft of the long bone
Hollow, cylindrical shape & thick compact bone
Function is to provide strong support without cumbersome weight
Both ends of a long bone, made of cancellous bone filled with marrow
"Bulbous shape" function is to provide attachments for muscles and give stability to joints
Articular cartilage
Layer of hyaline cartilage that covers the articular surface of epiphyses
Articular cartilage
Function is to cushion jolts & blows
Dense, white fibrous membrane that covers bone
Attaches tendons firmly to bones
Contains cells that form & destroy bone
Contains blood vessels important in growth & repair
Contains blood vessels that send branches into bone
Essential for bone cell survival & bone formation
Medullary cavity
Tubelike, hollow space in the diaphysis
Medullary cavity
Filled with yellow marrow in adults; red marrow in children
Short, flat & irregular bones
Inner portion is cancellous bone covered on the outside with compact bone
Short, flat & irregular bones
Spaces inside the cancellous bone of a few irregular & flat bones are filled with red marrow
Bone tissue
Most distinctive form of connective tissue
Hard & calcified
Bone tissues extracellular components are
Rigidity of bone
Allows it to serve its supportive & protective functions
Tensile strength
Strength nearly equal to that of cast iron at less than one third the weight
3 inorganic salts in bone tissue
hydroxyapatite, magnesium, sodium
Highly specialized chemical crystals of calcium & phosphate contribute to bone hardness
Inorganic salts
Slender needlelike crystals are oriented to most effectively resist & mechanical deformation
Composition of bone matrix
Inorganic salts, Measuring bone mineral density, organic matrix
organic matrix
Composite of collagenous fibers and an amorphous mixture of protein & polysaccharides called ground substance
ground substance
Is secreted by connective tissue cells
organic matrix
Adds to overall strength of the bone & gives some degree of resilience to bone
Compact bone
Contains many cylinder- shaped structural units called osteons or haversian systems
Surround canals that run lengthwise through bone and are connected by tranverse Volkmann canals
Lamella, Lacunae, Canaliculi, Haversian canal
Four types of structure make up each osteon
Concentric, cylinder-shaped layers of calcified matrix
Small spaces containing tissue fluid in which bone cells are located between hard layers of the lamella
Ultra small canals radiating in all directions from the lacunae & connecting them to each other and to the haversian canal
Haversian canal
Extends lengthwise through the center or each osteon and contains blood vessels & lymphatic vessels
No osteons in cancellous bone; instead, it has
Tiny canaliculi
Nutrient's are delivered & waste products removed by diffusion through
body spicules
Arranged along lines of stress to enhance the bone's strength
Cancellous bone
Spongy bone constitutes about 20% of total bone mass
Bone cells
Metabolically active & need a blood supply, which comes from the bone marrow in the internal medullary cavity of cancellous bone
Compact bone "blood supply"
Addition to bone marrow & blood vessels from the periosteum, penetrate bone & then, by way of Volkmann canals, connect with vessels in the haversian canals
Types of bone cells
osteoblast, osteoclast, and osteocytes
Bone forming cells found in all bone surfaces
Small cells synthesize & secrete osteoid, an important part of the ground substance
Collagen fibrils line up in osteoid and serve as a framework for the deposition of calcium & phosphate
Giant multi nucleated cells
Responsible for the active erosion of bone minerals
Contain large numbers of mitochondria & lysosomes
Mature non dividing osteoblasts surrounded by matrix & lying within lacunae
myeloid tissue
Specialized type of soft, diffuse connective tissue
Bone marrow
Site for production of blood cells
Bone marrow
Found in the medullary cavity of long bones & in the spaces of spongy bone
Red bone marrow
Found in virtually all bones in an infant's or child's body
Red bone marrow
Functions to produce red blood cells
Yellow marrow
Replace red marrow as individual ages
Yellow marrow
Marrow cells saturated with fat & are no longer active in blood cell production
Ribs, Bodies of vertebrea, Humerus, Pelvis, Femur
Main bones in an adult that still contain red marrow
Decreased Blood Supply
Yellow marrow can change to red marrow during times of
Functions of bone
Support, Protection, Movement, Mineral storage, Hematopoiesis
"Bones" Support
Form the framework of the body & contribute shape, alignment & positioning of body parts
"Bones" Protection
Protect the delicate structures they enclose
"Bones" Movement
Their joints constitute levers that move as muscles contract
"Bones" Mineral Storage
Major reservoir for calcium, phosphorous & other minerals
Bone "hematopoiesis"
Blood cell formation is carried out by myeloid tissue
Skeletal System
Serves as a storehouse for about 98% of body calcium reserves
Mobilized & moves into & out of blood during bone remodeling
Remove calcium from blood & lower circulating levels during bone formation
Release calcium into blood & increase circulating levels during breakdown of bone
Homeostasis of calcium ion concentration essential for
Bone formation, remodeling, repair; blood clotting; transmission of nerve impulses; maintenance of skeletal & cardiac muscle contraction
Parathyroid hormone calcitonin
Mechanisms of calcium homeostasis
Parathyroid hormone
Primary regulator of calcium homeostasis
Parathyroid hormone
Stimulates osteoclasts to initiate breakdown of bone matrix & increase blood calcium levels
Parathyroid hormone
Increases renal absorption of calcium from urine
Parathyroid hormone
Stimulates vitamin D synthesis
Protein hormone produced in the thyroid gland
Produced in response to high blood calcium levels
Stimulates bone deposition by osteoblasts
Inhibites Osteoclast activity
Far less important in homeostasis of blood calcium levels than parathyroid hormone
Development of bone from small cartilage model to adult bone
Intramembranous ossification
Occurs within a connective tissue membrane
Flat bones
Begin when groups of cells differentiate into osteoblasts
Clustered together in centers of ossification
Secrete matrix material and collagenous fibrils
Ground Substance
Large amounts of "what" accumulate around each osteoblast
Collagenous fibers
Become embedded in the ground substance & constitute the bone matrix
Bone matrix
Calcifies when calcium salts are deposited
Appear and join in a network to form spongy bone
Appositional growth
Growth occurs by adding osseous tissue
Primary ossification of endochondral ossification
Center of bone forms blood vessel enters the cartilage model at the midpoint of diaphysis bone grow in length as endochondral ossification progresses from the diaphysis toward each epiphysis
Develops and enlarges to produce a collar of bone
Endochondral Ossification
Most bones begin as a cartilage model with bone formation spreading essentially from the center to the ends
Secondary Ossification
Centers appear in the epiphysis, and bone growth proceeds toward the diaphysis
Epiphyseal Plate
Remains between the diaphysis and each epiphysis until bone growth in length is complete
Four layers of epiphyseal plate
"resting" cartilage cells, zone of proliferation, zone of hypertrophy, zone of calcification
Resting cartilage cells
Point of attachment joining the epiphysis to the shaft
Zone of Proliferation
Cartilage cells undergoing active mitosis, which causes the layer to thicken and the plate to increase in length
Zone of Hypertrophy
Older, enlarged cells undergoing degenerative changes associated with calcium deposition
Zone of Calcification
Dead or dying cartilage cells undergoing rapid calcification
Osteoclast & Osteoblast
Bones grow in diameter by the combined action of
Enlarge the diameter of the medullary cavity
From the periosteum build new bone around the outside of the bone
Break in the continuity of a bone
Fractures do what to blood vessels that carry nutrients to osteocytes
Tear & destroys blood vessels
Vascular damage
Initiates repair sequence in bone fractures
Specialized repair tissue that binds the broken ends of the fracture together
Fracture Hematoma
Blood clot occurring immediately after the fracture, which is then resorbed and replaced by callus
Characteristics of Cartilage
Avascular connective tissue; fibers are embedded in a firm gel; has the flexibility of firm plastic; no canal system or blood vessels
Receive oxygen & nutrients by diffusion
Fibrous covering of the cartilage
Cartilage types
Differ because of the amount of matrix present and the amounts of elastic & collagenous fibers
Types of cartilage
Hyaline, Elastic, Fibro
Hyaline cartilage
Covers the articular surfaces of bones
Hyaline cartilage
Most common type of cartilage
Hyaline cartilage
Forms the costal cartilages, cartilage rings in the trachea, bronchi of the lungs and the tip of the nose
Hyaline cartilage
Forms from specialized cells in centers of chondrification, which secrete matrix material
Chondrocytes are isolated into
Elastic Cartilage
Forms external ear, epiglottis & Eustachian tubes
Elastic Cartilage
Large # of elastic fibers confers elasticity & resiliency
Fibro cartilage
Occurs in symphysis pubis & intervertebral disks
Fibro cartilage
Small quantities of matrix & abundant fibrous elements
Fibro cartilage
Strong & rigid type of cartilage
Gristle like nature
Permits cartilage to sustain great weight or serve as a shock absorber
Strong yet pliable support structure
Permits growth in length of long bones
Interstitial or endogenous growth
Cartilage cells divide & secrete additional matrix; seen during childhood & early adolescence while cartilage is still soft & capable of expansion from within
Appositional or exogenous growth
Chondrocytes in the deep layer of the perichondrium divide & secrete matrix; new matrix is deposited on the surface, thereby increasing its size; unusual in early childhood but once initiated continues throughout life
Skeleton fully ossified by what age?
Soft tissue
What tissue may continue to grow- ossifies more slowly
Increased density and strength from exercise occurs as
Decreased density & strength from pregnancy, nutritional deficiencies and illness occur as
Advanced adulthood
What cycle of life does: hard bone matrix replaced by softer connective tissue; exercise can counteract degeneration

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