Lecture 39: Histology and Embryology of Cartilage and Bone

Question 1

What occurs at the proliferation zone at the epiphyseal plate of growing long bone?

Answer 1

Chondroblasts quickly divide and push the epiphysis away from the diaphysis, lengthening the bone

Question 2

Which zone at the epiphyseal plate of growing long bone has older chondrocytes enlarging and signaling the surrounding matrix to calcify?

Answer 2

Hypertrophic zone

Question 3

What occurs at the calcification zone at the epiphyseal plate of growing long bone?

Answer 3

Matrix becomes calcified; chondrocytes die, leaving behind trabeculae-shaped calcified cartilage (NOT bone yet)

Question 4

At the ossification zone (metaphysis), _____ digest the calcified cartilage and _____ replace it with actual bone tissue in the shape of the calcified cartilage, resulting in ______.

Answer 4

osteoclasts. osteoblasts, bone trabeculae

Question 5

What zone at the epiphyseal plate of growing long bone has small, inactive cartilage cells?

Answer 5

Resting zone

Question 6

What comprises the histological appearance of cartilage?

Answer 6

cells (chondrocytes, cartilage cells) and matrix (ECM) composed of collagen fibers, ground substance, and water

Question 7

What are the three cartilage tissue types?

Answer 7

fibrous, elastic, and hyaline

Question 8

Which cartilage tissue type has type I collagen fibers visible in the matrix and NO perichondrium?

Answer 8

Fibrous

Question 9

What type of cartilage comprises intervertebral discs, the pubic symphysis, knee joints, tendons, and ligament insertions into bone?

Answer 9

Fibrous

Question 10

Which type of cartilage has type II collagen and elastin in its matrix and where is it found?

Answer 10

Elastic found in ear and epiglottis

Question 11

What are the defining features of hyaline cartilage and where is it found?

Answer 11

Type II collagen, homogeneous matrix (smooth appearance), and fibers NOT visible in matrix
Found in respiratory tract, ventral ends of ribs, synovial joints, and growth plates of extremity long bones

Question 12

What are the three cartilage cell types?

Answer 12

Perichondrial cells (mesenchymal precursors) 
Chondroblasts (divide, grow, synthesize matrix)
Chondrocytes (maintain matrix)

Question 13

What are the two types of cartilage growth?

Answer 13

Appositional (perichondrial derived, at the periphery, adds width)
Interstitial (isogenous groups of chondroblasts, at growth plate, adds length)

Question 14

What type of cartilage growth comprises chondroblast division, produces cell clusters where each cell make matrix, pushing it apart from sister cells, and where cartilage can expand from within because the matrix is gel?

Answer 14

Interstitial (isogenous groups)

Question 15

What type of cartilage growth comprises the growth plate?

Answer 15

long rows of isogenous groups of chondroblasts doing interstitial growth (in proliferation zone)

Question 16

What is the primary histological difference between cartilage matrix and bone matrix?

Answer 16

bone matrix = osteoid and crystals (not found in cartilage

Question 17

What is osteoid?

Answer 17

uncalcified pre-bone

Question 18

Most of the skeleton begins as cartilaginous template that then ossifies to become bone. This process of converting cartilage to bone is called _____.

Answer 18

endochondral ossification

Question 19

What are the four bone cell types?

Answer 19

Osteoprogenitor cells
Osteoblast
Osteocyte
Osteoclast

Question 20

What are osteoid canaliculi?

Answer 20

small channels that contain cytoplasmic processes from osteocytes; they communicate with other osteocytes via gap junctions

Question 21

What type of bone growth utilizes the membrane model, features appositional growth at the periosteum, contributes to long bone width, and histology will show bone but never cartilage?

Answer 21

Intramembranous bone formation

Question 22

What type of bone growth utilizes the hyaline cartilage model, features interstitial growth at the growth plate, contributes to long bone length, and histology will show bone AND cartilage?

Answer 22

Endochondral bone formation

Question 23

Describe the embryological formation of long bones.

Answer 23

mesenchyme condenses, chondrocytes make cartilage model, blood vessels bring mineralization, and osteoblasts make bone

Question 24

Bone cap is to _____.

Answer 24

epiphysis

Question 25

The ossifying region next to the growth plate is to _________.

Answer 25

metaphysis

Question 26

Bone shaft is to _____.

Answer 26

diaphysis

Question 27

What occurs at the growth plate?

Answer 27

chondrocytes are dividing and making matrix

Question 28

What occurs at the metaphysis?

Answer 28

osteoblasts are differentiating into osteocytes

Question 29

What type of ossification occurs at the skull vault, sesamoids, and at bone periphery?

Answer 29

Intramembranous appositional ossification

Question 30

What type of ossification occurs at both bone and cartilage (eg. long bone metaphysis)?

Answer 30

Endochondral interstitial ossification

Question 31

describe cancellous/spongy/trabecular bone.

Answer 31

formed of right-angled struts, which distribute force over a large area to cortex preventing bone from breaking at stress points, marrow or fat fills the spaces between trabeculae, found at core, long bone joints, and at skull dipole

Question 32

Describe compact/cortical bone.

Answer 32

Solid perimeter; contains circumferential lamellae and Haversian osteons which account for most of the bone weight

Question 33

Describe circumferential lamellae.

Answer 33

contain type I collagen fibers in parallel layers, with fibers oriented at a 45 degree angle relative to adjacent layers
Parfait-like

Question 34

Describe Haversian osteons.

Answer 34

contain type I collagen fibers in concentric layers with fibers oriented at a 45 degree angle relative to adjacent rings; arranged around a central canal (Haversian canal) containing blood vessels and nerves and connected to neighboring canals by perpendicular Volkmann’s canals
Onion-like

Question 35

Describe osteogenesis.

Answer 35

Old osteon resorbed by osteoclasts at cutting cone tip, new osteon built by osteoblasts in cutting cone shaft, new Haversian system formed and layers added to canal lumen causing narrowing, osteoblasts transform into osteocytes and are buried alive within the layers

Question 36

What are the two bone fiber arrangements occurring in both compact and cancellous bone?

Answer 36

Woven and lamellar

Question 37

All bone starts as _____ and becomes _____.

Answer 37

woven

lamellar

Question 38

Bone is made from membrane or cartilage ossification and remodeled how?

Answer 38

mineralization of membrane/cartilage, chondrocyte death (endochondral), osteoclasts digest mineralized hyaline cartilage (endochondral), osteoblasts make woven bone, osteoclasts and osteoblasts remodel woven bone into lamellar bone (intramembranous)

Question 39

What three phases comprise fractured bone healing and remodeling?

Answer 39

Reactive phase
Reparative phase
Remodeling phase

Question 40

What are the two major differences between cartilage matrix and bone matrix?

Answer 40

cartilage matrix contains both type I and II collagen whereas bone matrix only contains type I
cartilage contains NO crystals and thus has a low mineral content whereas bone matrix contains crystals and thus has a high mineral content

Question 41

Cartilage cells contain NO cells that resorb the matrix. (True/False)

Answer 41

True