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Functional properties of hyaline cartilage

Provides support, flexibility, and resilience for articular, costal, respiratory, and nasal region.


Functional properties of elastic cartilage

Provides elasticity in external ear and epiglottis


Functional properties of fibrocartilage

thick collagen fibers provide tensile strength for the menisci of the knee and the vertebral discs. (also in pubic symphosis)


Cartilage growth: appositional

cells secrete matrix against external face of existing cartilage


Cartilage growth: interstitial

chondrocytes divide and secrete new matrix, expanding cartilage from within.


2 major groups of the skeleton

axial: skull, vertebrae, rib cage
appendicular: limbs, girdles (shoulder, pelvic)


4 bone classes

long bones: longer than they are wide. ex, limbs.

short bones: cube-shaped bones. ex, wrist & ankle

flat bones: thin, flat, and slightly curved. ex, sternum, scapula, ribs, most skull bones.

irregular bones: anything else. ex, vertebrae, coxal bones.


7 important functions of bones

1. support - for body & soft organs

2. protection - brain, spine, vital organs

3. movement - levers for muscle action

4. mineral & growth factor storage - Ca + phosphorus, growth factors reservoir

5. blood cell formation - blood cell formation in red marrow cavities in certain bones (hematopoiesis)

6. triglyceride (fat) storage - fuel / energy

7. hormone production - osteocalcin - regulates bone formation, protects from obesity, glucose intolerance, diabetes.


gross anatomy of long bones

composed of spongy (trabeculae, honeycomb) and compact bone (dense outer layer, smooth & solid)

has 2 epiphyses (ends) and the middle piece is the diaphysis. between the epiphyses and the diaphysis is the epiphyseal line (plate in younger people).

bone is lined with periosteum, and inner medullary cavity is lined with endosteum. inside is yellow bone marrow.

Joints are covered by articular cartilage


gross anatomy of flat bone

thin plates of spongy bone covered by compact bone. plates are sandwiched between connective tissue membranes (periosteum, endostum).

no shaft or epiphyses, bone marrow throughout spongy bone, but no marrow cavity.

hyaline cartilage covers articular surfaces.


microscopic anatomy of compact bone

5 types of cells:
osteogenic, osteoblasts, osteocytes, bone lineing cells (periosteal / endosteal), and osteoclasts



mitotically active stem cells in periosteum and endosteum. when they are stimulated, they differentiate into osteoblasts (bone forming) or revert back to more osteogenic cells



bone forming cells, secrete unmineralized bone matrix (osteoid) - includes collagen and Ca-binding proteins. actively mitotic.



mature bone cells in lacunae. they monitor and maintain bone matrix. respond to strain and stress and communicate with osteoblasts and osteoclasts for bone remodeling.


bone-lining cells

periosteal/endosteal: flat cells on bone surfaces which maintain matrix.



break down bone - hematopoietic stem cells that become macrophages. rest in resorption bay and have a ruffled border to increase surface area for enzyme degradation of bone and seals off area from surrounding matrix.


microscopic anatomy of compact bone

osteon: structural unit of compact bone - cylinder parallel to the long axis of the bone.

elongated cylinder parallel to the long axis of bone

lamellae - hollow tubes of bone matrix; collagen fibers in the same ring run in the same direction, but adjacent rings run in different directions to withstand stress and resist twisting

central canal runs through core of osteon which contains blood vessels and nerve fibers.

volkmann's canals run perpendicular to canal, and connect blood vessels and nervs of periosteum, medullary cavity, and central canal.

lacunae - small cavities that contain osteocytes.

canalculi = hairline canals that connect lacunae to each other and central canal.


microscopic anatomy of spongy bone

appears poorly organized, with trabeculae

contain irregularly arranged lamellae and ostoecytes interconnected by canalculi. capillaries in endosteum supply nutrients.


organic components of the chemical composition of bone

osteogenic cells, osteoblasts, osteocytes, bone-lining cells, osteoclasts, osteoids.

1/3 of organic bone matrix is secreted by osteoblasts (made up of ground substance, collagen fibers, and contributes to structure; provides tensile strength, flexibility)


inorganic components of chemical composition of bone

hydroxyapatites (mineral salts) - 65% of bone by mass, mainly of tiny calcium phosphate crystals in and around collagen fibers

responsible for hardness and resistance to compression


intramembranous ossification

bone develops from fibrous membrane, resulting in a membrane bone (flat bones, like clavicles and cranial bones)


endochondral ossification

bone forms by replacing hyaline carilage. bones are called cartilage bones, forms most of skeleton.


interstitial growth: growth in length of long bones

requires presence of epiphyseal cartilage

epiphyseal plate maintains constant thickness - rate of cartilage growth on one side balanced by bone replacement on the other.

concurrent remodeling of epiphyseal ends to maintain proportion


interstitial growth zones

1. resting zone - cartilage on epiphyseal side of epiphyseal plate (inactive)

2. proliferation zone: cartilage on diaphysis side of epiphyseal plate, rapidly divide pushing epiphysis away from diaphysis

3. hypertrophic zone: older chondrocytes which erode and enlarge, leaving interconnected spaces

4. calcification zone: surrounding cartilage matrix calcifies, chondrocytes die and deteriorate

5. ossification zone: stalagtite-looking, osteoclasts erode spicules and osteoblasts cover them with new bone, ultimately spongy bone replaces them


bone remodeling components

osteoblasts: secrete new bone matrix (bone deposit)

dig depressions and grooves as they break down matrix, secret lysosomal enzymes that digest matrix and protons, acidity converts salts to soluble forms.
-they also fagotize demineralized matrix and dead osteocytes


primary ossification center

begins in center of shaft, blood vessel infiltration of perichondrium converts it to periosteum


secondary ossification center

appear in epiphyses


vitamin d's affect on bone growth and development

increases the flow of calcium into the blood stream by promoting absorption of calcium from food.


somatotropin (growth hormone)'s affect on bone growth and development

stimulates epiphyseal plate activity in infancy and childhood


thyroid hormone's affect on bone growth and development

modulates activity of growth hormone, ensures proper proportions


calcitonin's affect on bone growth and development

reduces blood calcium, opposing the effects of PTH. works with PTH so maintain homeostasis.


parathyroid hormone's affect on bone growth and development

removes calcium from bone regardless of bone integrity. works with calcitonin to maintain homeostasis.


androgen's affect on bone growth and development

sex hormones help maintain health & normal density of the skeleton by restraining osteoclasts and promoting deposit of new bone. after menopause, estrogen levels drop and deficiency is strongly implicated in osteoporosis in older women.


physical stress associated with exercise's affect on bone growth and development

weight bearing exercise increases bone mass above normal values and provide a greater buffer against age-related bone loss


fractures: comminuted

bone fragments into three or more pieces


fractures: compression

bone is crushed. comon in porous bones subjected to extreme trauma, like a fall.


fractures: spiral

ragged break occurs when excessive twisting forces are applied to bone - common sports fracture


fractures: epiphyseal

epiphyseal separates from the diaphysis along the epiphyseal plate - occurs when cartilage cells are dying and calcification of the matrix is occurring


fractures: depressed

broken bone portion is pressed inward - skull fracture


fractures: greenstick

bone breaks incompletely, like a green twig. only one side breaks, other side bends. common in children whose bones have relatively more organic matrix are more flexible than adults.


hematoma forms (collection of blood) - clot forms, site is swollen, painful, and inflamed

1st step in fracture repair


fibrocartilaginous callus forms -

capillaries grow into hematoma,
phagocytic cells clear debris,
fibroblasts secrete collagen fibers to span break and connect broken ends,
fibroblasts, cartilage, and osteogenic cells begin reconstruction of bone
mass of repair tissue called fibroartilaginous callus

2nd step in fracture repair


bony callus forms

in 1 week, new trabeculae appear in fibrocartilaginous callus,
callus converted to bony (hard) callus of spongy bone
~2 months later firm union forms

3rd step in fracture repair


bone remodeling occurs

begins during body callus formation
continues for several months
excess material on diaphysis exterior and within medullary cavity removed
compact bone laid down to reconstruct shaft walls
final structure resembles original because responds to same mechanical stressors

4th step of fracture repair



bones poorly mineralized
calcium salts not adequate
soft, weak bones
pain upon bearing weight

rickets (osteomalacia of children)



bone resorption outpaces deposit
spongy bone of spine and neck of femur most susceptible (vertebrae/hip fractures most common)


paget's disease

excessive and haphazard bone deposit and resorption - bone is made fast and poorly - called pagetic bone

high ratio of spongy to compact bone and reduced mineralization

occurs in spine, pelvis, femur, and skull