Bone

Question 1

Intramembranous Ossification

Answer 1

Through the mesenchymal skeleton
Bone Formed: skull, mandible, clavicle
Bone remodeling : osteoblasts secrete osteoid and calcify to become osteocytes, forms spongy bone and build outwards where outer spongy layer becomes compact bone

Question 2

Endochondral Ossification

Answer 2

Mesechymal Skeleton —> Hylane Cartilage —> Bone
Most Bones Formed stopping after skeletal maturity

Cartilage Model: Chondroblasts forming cartilage, Insterstital ( cartilage within growth, Length - primiary ossification ), Appositional ( outer surface growth, width - thick-secondary ossification)

bone forms on a hyaline cartilage template, all bones except intramembranous ones, form bone collar, primary ossification along diaphysis secondary ossification is at epiphyses and these are separated at a growth plate, 5 zones in the growth plate for this

Question 3

Bone growth at Epiphyseal Plates

Answer 3

Epiphyseal plate is where growth continues until you stop growing, in both directions towards the plate

Calcification on diaphysis side, replace cartilage with bone to grow, Cartilage cells stop dividing and become bone into adolescence

Add layers of compact bone to increase width

Question 4

Osteoblasts

Answer 4

mesenchymal OPG

Build Bone

Question 5

Osteocytes

Answer 5

Cells, maintain daily metabolism

mature osteoblast trapped by calcification, communicate via gap junctions and use canaliculi to send signals or nutrients

Question 6

Osteoclasts

Answer 6

Crush Bone

large/multinucleated cells, remodel by removing calcified cells, Howship’s lacuna is the enzyme secreted to do this, ruffled border for proper function

Question 7

Therapies to preserve bone and prevent resportion

Answer 7

PTH promotes bone resorption to release Ca from bone into blood,

CT takes Ca from blood to add to bone - inhibit OC activity

OPG prevents resorption and preserves bone, RANKL does opposite

Hormones/SERMs slow osteoclasts/promote formation

Bisphosphonates – interfere with ruffled membrane to not allow resorptive

Question 8

Signaling Mediators for Bone remodeling

Answer 8

Bone is 99% of body’s calcium, regulated by hormones: parathyroid hormone and calcitonin.

PTH promotes bone resorption to release Ca from bone into blood, CT takes Ca from blood to add to bone

RANK – immature osteoclasts
RANKL – expressed by osteoblasts, stimulated by PTH to have osteoblasts secrete/produce this, binds RANK and leads to bone resorption by osteoclasts

OPG – secreted by osteoblasts, competes to bind RANK, will inhibit osteoclast and not let you break down bone

Question 9

Primary “Immature or Woven” Bone

Answer 9

fetal development & young adolescent (OC and Collagen I)

Question 10

Secondary “Mature or Lamellar” Bone

Answer 10

OC in lacunae by canaliculi, osteons around HC (contain nutrients for bone growth), VC perpendicular to HC connect osteons)

Question 11

Compact “cortical” Bone

Answer 11

hard external layer of osteons enclosing OC enclosed in lacunae

Question 12

Spongy “Trabecular” Bone

Answer 12

network of spicules or trabeculae, no osteons, spongy

Question 13

5 Zones of Bone Formation

Answer 13

Reserve zone - sit

Zone of proliferation - divide

Zone of maturation/hypertrophy - enlarge

Calcified cartilage zone – dying, trigger CaPO4 deposits, basophilic

Ossification zone – secrete osteoid to form bone