Bone Physiology

core functions of skeleton

support, protection, lever system/movement

bone is a storage depot for

calcium and phosphate salts

hematopoesis

production of blood cells occuring in bone marrow

bone classificaions

long, short, flat, irregular, sesamoid

long bone example

femur

short bone example

tarsals

flat bone example

frontal bone

irregular bone example

sphenoid/vertebrae

sesamoid bone example

patella

gross structure of long bone

diaphysis, metaphysis, epiphysis, medullary cavity, epiphyseal plate, articular cartilage, periosteum, endosteum

diaphysis

tubular shaft forming long axis; contains compact bone

metaphysis

narrow bone connecting diaphysis to epiphysis; contains growth plate

epiphysis

expanded ends of bone; contains spongy bone

medullary cavity

central hollow cavity within shaft filled with marrow; red and yellow marrow

red marrow

active site of hematopoesis

yellow marrow

inactive site with adipose tissue

epiphyseal plate

hyaline cartilage plate in growing bone; mineralizes into bony line after end of growth

articular cartilage

smooth hyaline cartilage covering joint surfaces to reduce friction

periosteum

membrane covering outer surface of the bone

endosteum

membrane lining internal surfaces

part of compact bone

osteon, central canal, volkmans canal, concentric lamellae, interstitial lamellae, lacunae, canaliculi

features of compact bone

dense, solid outer layer used for weight bearing

osteon

structural unit of compact bone

central canal

contains blood vessels and nerves in the center of osteon

volkman/perforating canal

connects blood supply from periosteum to central canals

concentric lamellae

rings of matrix surrounding central canal

interstitial lamellae

remanents of old osteons filling gaps between intact osteons

lacunae

small cavities containing osteocytes

canaliculi

hair like canals connecting lacunae to each other and central canals

features of spongy bone

honeycomb network of trabeculae and red bone marrow; lightweight

cell types of bone

osteoprogenitors, osteoblasts, osteocytes, osteoclasts

osteoprogenitors

stem cells that divide to produce osteoblasts

osteoblasts

bone forming cell; secretes hydroxyapetite

osteocyte

mature bone cell maintaining matrix

osteoclast

cell responsible for resorption/breakdown

in early stages of life, fetal skeletons are made of

connective tissue membranes (mesenchyme) and hyaline cartilage

2 types of bone formation

intramembranous ossification, endochondral ossification

intramembranous ossification

bone forms directly from mesenchymal connective tissue; fonatelles

fonatelles

unossified membranous spaces (soft spots) in fetal skull providing flexibility during childbirth

endochondral ossification

bone forms from replacing hyaline cartilage; most bones below skull base

2 types of bone growth mechanisms

interstitial and appositional growth

interstitial growth

growths in length; occurs at epiphyseal plate

steps of interstitial growth

zone of resting cartilage, proliferating cartilage, hypertrophic cartilage, calcified cartilage, ossification

appositional growh

growths in width; deposition of new bone on outer surfaces; usually happens when weight bearing increases

wolff’s law

bones adjust architecture, thickness, and density in response to mechanical stress placed upon them; increased and decreased loads

increased load

stimulates osteoblast activity/growth

decreased load

stimulates osteoclast activity, thins and weakens

parathyroid hormone (PTH)

released by parathyroid gland when calcum is too high; increases plasma calcium levels

calcitonin

released by thyroid gland when calcium levels too high; decreases plasma calcium levels

osteoporosis

disease featuring low bone mass/deterioration; high risk of compression fractures

steps of bone repair process

hematoma, soft callus, bony callus, remodeling

hematoma

mass of blood clotting forms at fracture

soft callus

capillaries grow; collagen/cartilage bridge break

bony callus

osteoblasts make soft callus into spongy bone

remodeling

excess material removed; compact bone reconstructed

closed fracture (simple)

bone breaks cleanly without penetrating skin

open (compound)

broken ends of bone pierce through skin

transverse break

fracture runs straight across long axis of bone

spiral break

fracture wraps around shaft due to twisting

comminuted break

bone splinters or breaks into 3+ fragments

impacted break

broken bone ends driven into each other

greenstick

incomplete break: one side breaks while other bends; common in children

oblique break

fracture line runs diagonally across bone shaft