skeletal system - functions, organization, classification

basic functions of skeletal system (6)

• support

• protection

• movement

• storage of calcium

• production of blood cells

• storage of chemical energy

support function

• provides framework for body by supporting soft tissues

• provides points of attachment for skeletal muscles

protection function

• protects many internal organs from injury

  • examples include cranium (brain), vertebrae (spinal cord), and ribs (heart/lungs)

movement function

contraction of muscles pulls on bones; together muscles and bones produce movement

storage of calcium function

bones release minerals into blood to maintain homeostasis when needed

production of blood cells function

• red bone marrow - produces RBCs, WBCs, and platelets

• present in fetal/infant bones and also some adult bones (pelvis, ribs, sternum, skull, ends of arm/leg bones)

storage of chemical energy

yellow bone marrow stores fat/reserve energy

axial skeleton structures

• skull (facial/cranial)

• verebral column (sacrum/coccyx)

• sternum

• ribs

appendicular skeleton structures

• hands/feet

• wrist/ankle

• arm/leg

• pectoral/pelvic girdle

long bones

greater length than width, with long shaft

• ex: femur, tibia/fibula, humerus, ulna and radius, phalanges

short bones

somewhat cube-shaped; nearly equal in length and width

• ex: carpals/tarsals

flat bones

generally thin; extensive surface for muscle attachment; provide considerable protection

• ex: cranial bones, sternum, ribs, scapulae

irregular bones

complex shapes (don’t fit into other categories)

• ex: vertebrae of backbone; some facial bones

sesamoid bones

pretect tendons from wear and tear

• ex: patella

diaphysis

long cylindrical, main portion of long bone

epiphysis

distal and proximal ends of long bone

metaphysis

regions in mature long bone where epiphysis meets diaphysis

• includes epihyseal plate

epiphyseal plate

layer of cartilage that is being replaced by bone; bone grows in length

• when growth stops, cartilage is replaced by bone creating epiphyseal line

articular cartilage

reduces friction/absorbs shock

spongy bone

• contains red marrow; found in hip bones, ribs, breast bones, vertebrae, and ends of long bone

• irregular, criss-crossing of thin columns of bone

  • spaces within the spongy bone are filled with red bone marrow

compact bone

• contains few spaces

• external layer of all bones of the body and the bulk of the body of long bones

• provides protection/support/resistance to stress

marrow cavity

space within the diaphysis which contains fatty yellow marrow in adults

periosteum

• tough sheath of dense irregular connective tissue; surrounds bone surface

• protects

• assists in fracture repair

• helps nourish bone

• serves as point of attachment for ligaments/tendons

endosteum

lines the surface of marrow cavity, contains bone forming cells that contribute to growth in width of the bone

tissue making up bones

osseous tissue

bone matrix composition

• 25% water

• 25% protein fibers

• 50% crystallized mineral salts

calcification

in the matrix abundant mineral salts are deposited into a framework formed by collagen fibers; they crystallize and the tissue hardens

hardness

depends on crystallized inorganic mineral salts

flexibility

depends on collagen fibers

cells making up bone

• osteogenic cells

• osteoblasts

• osteocytes

• osteoclasts

osteogenic cells

unspecialized stem cells which divide into cells that develop into osteoblasts

• found along the inner portion of the periosteum, endosteum, and canals within the bone containing blood vessels

osteoblasts

• bone building, do not divide

• synthesize and secrete collagen

• initiate calcification

• found on surface of the bone

• as they secrete matrix materails they become trapped in their secretions and become osteocytes

osteoclasts

• huge cells found in bone which release powerful lysosomal enzymes that function in the destruction of bone matrix

resorption

destruction of bone matrix

• part of normal development, growth, maintenance, and repair of bone

osteoperosis

weaking of bones over time; more common in women

compact bone structures

• volkmann’s canals

• central (haversian) canals

• concentric lamellae

• lacunae

• canaliculi

• osteons

volkmann’s canal

locations where blood/lymph vessels and nerves from periosteum penetrate transversely the width of bones

• connect with those of the periosteum, medullary cavity, and central canals

central (haversian) canals

extend vertically, lengthwise through the bone

concentric lamellae

rings of hard, calcified matrix surrounding central canals

lacunae

small spaces between lamellae that contain osteocytes

canaliculi

tiny channels that project in all directions from the lacunae

• provide routes for nutrients and oxygen to reach the osteocytes and wastes to be removed

osteon

a central canal with its surrounding lamellae, lacunae, and canaliculi

• part of Haversian system

trabeculae

irregular latticework of thin columns of bone

• part of spongy (cancellous) bone

cells in trabeculae

• osteocytes that lie in lacunae

• blood vessels from periosteum penetrate and supply nourishment to osteocytes

composition of trabeculae

• make up most flat, short, irregularly shaped bones

• found in epiphysis of long bones

• spongy bone found within in specific bones of the adult is the only site of red bone marrow and hematopoiesis