composed of: bones, associated ligaments, tendons and cartilages

• support

• protection

• reservoir for minerals and adipose tissue

• movement - muscles use bones to move body

• hematopoiesis - blood cell formation, made in bone marrow

• 206 in the human body, 2 groups

• axial skeleton: long axis of body, skull, vertebral column, rib cage

• appendicular skeleton: upper and lower limbs, girdles (shoulder bones and hip bones) that attach them to axial skeleton

  • locomotion and manipulation of the environment

  • clavicle and hips are not axial

4 types of bones

• long bones

  • all bones of limbs except patella

  • shaft + 2 extended ends

  • fingers are long bones!

• short bones

  • roughly cube shaped

  • bones of wrist and ankle

• flat bones

  • thin, flattened, little curved

  • sternum, scapulae, ribs and most of the skull

• irregular bones

  • weird shapes

  • vertebrae, hip bones, 2 skull bones (sphenoid and ethmoid)

bones are made of…

• osseous (bone) tissue

• fibrous connective tissue

• cartilage

• vascular tissue

• lymphatic tissue

• adipose tissue

• nervous tissue

all bones have an outer layer called compact bone and a honeycomb-like spongy bone

• bone is connective tissue, has cells + extracellular matrix

bone cells -

• osteoblasts: bone building cells, initiate calcification, secrete ECM, found in periosteum and endosteum

• osteocytes: mature bone cells, trapped in matrix, can’t secrete, maintains bone tissue

• osteoclasts: break down bone by digestive matrix

  • bone resorption

bone structure

• bony matrix: organic (1/3) and inorganic (2/3)

long bone structure

• shaft + 2 expanded ends

• shaft = diaphysis

• expanded ends = epiphyses

• external surface is covered by a 2x layered membrane, periosteum

2 types of bone marrow

• red bone marrow

  • blood cell forming tissue

• yellow bone marrow

  • no longer produces blood

osteogenesis: process of bone tissue formation, also called ossification

• before week 8, human is made of fibrous membranes and hyaline cartilage

• after week 8, bone tissue replaces membrane and cartilage

intermembranous ossification: bone replaces fibrous membranes, in bones of the skull, facial bones, clavicles, pelvis, scapulae and mandible

ossification center: location in tissue where ossification begins

• mesenchymal cells differentiate into osteoblasts

• initially, IM bone starts with spongy bone

• as growth slows, connective tissue becomes more organized

endochondral ossification: formation of hyaline cartilage that will be replaced by bone, more complex, most bones made this way

• chondrocytes increase in size, get deprived of nutrients then die

• blood vessels grow into perichondrium, goes to periosteum and thin layer of bone forms around the shaft

• diaphysis is filled with spongy bone

primary center of ossification: bone development begins here and spreads to both ends

secondary ossification center: capillaries and osteoblasts migrate to epiphysis to create this

fractures

• open (compound): bone ends penetrate skin

• closed (simple): don’t penetrate skin

• comminuted: break into 3+ pieces

• greenstick: breaks incompletely, one side bent, one side broken

• spiral: break caused by excessive twisting forces

• impacted: one fragment driven into the other

steps to repair

1. hematoma formation (large blood clot)

2. fibrocartilaginous callus formation (splints broken bone, forms spongy bone, clean broken bone)

3. bony callus formation

4. bone remodeling

wolf’s law: bone will grow/remodel in response to the forces or demands placed on it (ex weightlifting)

calcitriol: hormone that allows Ca+ and phosphate to absorb, can get by uv radiation

growth hormone: stimulate bone growth, produced by pituitary gland