Chapter 6: Skeletal System: Bone Tissue 2-3

zones of cartilage

resting

proliferating

hypertrophic

calcified

zone of resting cartilage

chondrocytes anchor plate to the epiphysis

no bone growth

zone of proliferating cartilage

chondrocytes divide and secrete matrix

zone of hypertrophic cartilage

maturing chondrocytes

zone of calcified cartilage 

chondrocytes die because cartilage matrix calcified; dissolved by osteoclasts

osteoblasts from diaphysis invade the area, lay down bone matrix 

‘new diaphysis’

epiphyseal plate closure

chondrocytes stop dividing and bone replaces remaining cartilage

18 yo in females

21 yo in males

how does medullary cavity get larger

osteoclasts along endosteum

minerals

calcium and phosphorus

• makes. bone ecm hard

magnesium

• helps form bone ecm

fluoride

• helps strengthen bone ecm

manganese

• activates enzymes involved with bone ecm synthesis

vitamins

A, C, D, K, and B12

vitamin c

need for collagen synthesis, main bone protein

vitamin d

UV light activates precursor molecule in stratum basale and stratum spinosum 

UV light exposure

10-15 min 2x/week

enzymes in liver and kidneys modify activated molecule

calcitriol

most active form of vitamin d

calcitriol

improves immune function

reduces inflammation

promotes Ca2+ absorption from food

bone growth hormones

insulin-like growth factors IGFs

T3 and T4

estrogen and testosterone

bone growth hormones during childhood

IGFs

produced in response to human growth hormone hGH

stimulates osteoblasts and protein synthesis

bone growth hormones thyroid hormones 

T3 and T4

stimulates osteoblasts 

bone growth hormones estrogen and testosterone

stimulates osteoblasts

growth spurt

bone remodeling

calcium homeostasis

PTH parathyroid hormone

calcitonin

PTH 

responds to low blood Ca2+ levels 

increases number and activity of osteoclasts - releases calcium from bone into blood 

decreases loss of Ca2+ in urine 

stimulates calcitriol - promotes Ca2+ absorption from food 

raises blood Ca2+ levels 

calcitonin

responds to high blood Ca2+ levels

inhibits osteoclasts 

speeds up blood Ca2+ uptake by bone 

stimulates osteoblasts 

lowers blood Ca2+ levels 

giantism 

oversecretion of hGH in childhood 

taller and heavier 

pituitary Dwarfism

undersecretion of hGH

<4ft 10in tall

osteoporosis

porous bones

osteoclasts > osteoblasts

more Ca2+ lost than gained from diet

fx risks

Dowager’s hump

women at higher risk for osteoporosis 

less bone mass

estrogen greatly declines at menopause 

men at risk for osteoporosis

testosterone decline more gradual

later decades

osteoporosis treatment

certain exercise

PT

fracture repair 

reactive phase- formation of fracture hematoma 

reparative phase 1- fibrocartilaginous callus formation 

reparative phase 2- bony callus formation 

bone remodeling phase 

Hulk’s Fist Breaks Ribs 

fracture 

break in a bone 

bone fracture types

closed/simple fracture - doesn’t penetrate skin

open/compound fracture - penetrates through skin

fracture treatment

reduction

immobilization

reduction 

realignment of broken bone ends 

open or closed 

fixation: internal or external (screws, plates, etc)

immobilization

6-8 weeks

ORIF - open reduction internal fixation

types of fractures

transverse

spiral

displaced

compression

greenstick

comminuted

epiphyseal

Pott’s

Colles