a&p chapter 6: skeletal system bones and joints

Functions of the Skeleton

5 main functions: support, protection, movement, mineral storage, blood cell production

Support means…

like beams of a house — holds body up and gives shape

Cartilage

bendy parts for smooth movement at joints

Ligaments

stretchy bands that tie bones together

Tendons

ropes that attach muscles to bones

Protection

bones act like armor (skull protects brain, ribs protect heart and lungs)

Movement is created when muscles…

pull on bones like ropes on levers

bones store _______ & __________ for strong bones, nerves, and muscles

calicum & phosphorus

bone marrow makes…

red blood cells, white blood cells, and platelets

Bone Matrix: _______ + _________ = strong, tough bone

35% organic (flexibility) + 65% inorganic (hardness)

Compact bone

hard, dense outer layer like a castle wall

Spongy bone

light, honeycomb structure inside bone ends and flat bones

Diaphysis

shaft of a long bone, made mostly of compact bone

Medullary cavity

hollow center of long bone with marrow inside

Epiphyses

bone ends, spongy inside and compact outside, covered in cartilage

Articular cartilage

smooth surface for joint movement

Epiphyseal plate

growth plate where bone lengthens (becomes epiphyseal line in adults)

Osteoblasts

builders 🛠️ — make new bone and become osteocytes when trapped

Osteocytes

maintainers 👷 — mature cells that keep bone healthy and sense stress

Osteoclasts

breakers 💥 — break down bone and release minerals into blood

Periosteum

outer covering of bone with blood vessels, nerves, and bone cells

Endosteum

inner lining of bone cavities with bone cells

Sharpey’s fibers

collagen fibers that anchor tendons and ligaments to bone

Intramembranous ossification

bone forms directly from connective tissue (flat skull bones, mandible, clavicle)

Fontanels

“soft spots” in babies that close by age 2

Endochondral ossification

bone replaces cartilage model (most bones form this way)

Growth plates allow __________ ______ until adulthood

lengthwise growth

Bone growth

length at plates (cartilage→bone) and width by osteoblast activity

Red bone marrow

makes blood cells

Yellow bone marrow

stores fat

Bone marrow in adults

mostly yellow except hip, ribs, sternum, skull, ends of femur/humerus

Marrow donation site

hip bone commonly used

206 bones in adults

babies have more; bones fuse over time

Axial skeleton

skull, hyoid, spine, rib cage

Appendicular skeleton

arms, legs, shoulder girdle, pelvic girdle

Long bones

ex. arms and legs

Short bones

ex. wrists and ankles

Flat bones

ex. skull, ribs, sternum

Irregular bones

ex. vertebrae, facial bones

Foramen

hole for nerves or blood vessels

Canal or Meatus

tunnel in bone

Fossa

depression or dent in bone

Tubercle or Tuberosity

round bump where muscle attaches

Process

sharp projection from bone where muscle attaches

Condyle

smooth rounded end that forms a joint

cranium/cranial bones

house and protect the brain

four principal sutures that connect cranial bones:

coronal, sagittal, lambdoid, and squamous

calvaria

top of the skull

frontal bone

forehead

supraorbital foramen/notch

allows passage of a blood vessel and nerve for eyelid and eye

anterior cranial fossa

supports lines of the brain

8 bones of the cranium

frontal, 2 parietal bones, 2 temporal bones, occipital bone, the sphenoid bone, and the ethmoid bone

3 parts of temporal bone

squamous part, tympanic part, and the petrous part

Open (compound) fracture

bone breaks through skin, infection risk

Closed (simple) fracture

bone broken, skin intact

Complicated fracture

bone and soft tissue damaged

Incomplete fracture

bone partly cracked

Greenstick fracture

bone bends and cracks like a twig

Hairline fracture

tiny crack

Complete fracture

bone broken into two or more pieces

Comminuted fracture

bone shattered into many pieces

Impacted fracture

bone ends jam together

Linear fracture

vertical break

Transverse fracture

horizontal break

Oblique fracture

diagonal break

Spiral fracture

twisting break

Stellate fracture

star-shaped cracks

Dentate fracture

jagged edges

Hematoma stage (fracture healing)

blood clot forms, swelling and inflammation start

Callus formation stage (fracture healing)

fibroblasts, osteoblasts, chondroblasts form soft bridge

Callus ossification stage (fracture healing)

soft callus replaced with spongy bone

Bone remodeling stage (fracture healing)

compact bone rebuilds, medullary cavity restored, fracture heals stronger

Calcium functions

strengthens bone, needed for muscle contraction, nerve signals, and cell activity

Parathyroid hormone (PTH)

raises blood calcium by activating osteoclasts, kidneys retain Ca²⁺, activates calcitriol

Calcitriol (active Vitamin D3)

raises blood calcium by increasing absorption from intestines

Calcitonin

lowers blood calcium by slowing osteoclast activity

Skull

protects brain; includes cranial and facial bones

Auditory ossicles

3 ear bones (malleus, incus, stapes) help with hearing

Hyoid bone

U-shaped bone in neck, helps with swallowing and tongue movement

Vertebral column

protects spinal cord; regions = cervical, thoracic, lumbar, sacrum, coccyx

Thoracic cage

ribs + sternum protect heart and lungs, assist breathing

Appendicular skeleton parts

upper limbs, lower limbs, pectoral girdle (shoulders), pelvic girdle (hips)

Normal bone

small pores, strong structure

Osteoporotic bone

large pores, weak structure

Osteoporosis

condition where bones become weak and brittle

Osteoporosis causes

low calcium, lack of exercise, family history, low estrogen

Osteoporosis prevention

weight-bearing exercise, calcium & vitamin D, medication

Hyperparathyroidism

parathyroid glands overproduce PTH → too much calcium released from bone