Cartilage and Bone

Question 1

3 types of cartilage

Answer 1

hyaline

elastic

fibrocartilage

Question 2

Why doesnt cartilage heal well?

Answer 2

Bc it is avascular and have immoble chondrocytes with limited proliferation

Question 3

Components of the Hyaline cartilage matrix

Answer 3

Homogenous amorphous matrix of:

• type II collagen
• GAGs
• proteoglycans
• glycoproteins

Question 4

Characteristics of Hyaline Cartilage

Answer 4

Chondrocytes located in lacunae

Hyaline cartilage has perichondrium except at articular surfaces

Low friction

Highly hydrated

calcifies with aging

Question 5

Componets of elastic cartilage matrix

Answer 5

Hyaline Matrix:

• proteoglycan
• glycoproteins
• type II collagen
• GAGs

PLUS elastic fibers and materials

Question 6

Charcteristics of elastic cartilage

Answer 6

elastic properties

doesnt calcify with aging

Question 7

Components of fibrocartilage

Answer 7

Hyaline cartilage PLUS dense regular connective tissue

Chondrocytes, some fibroblasts

Collagen fibers (type I and type II)

No perichondrium

Question 8

Characteristics of fibrocartilage

Answer 8

Resistance to compression and shearing (‘shock absorber’)

Intervertebral discs, symphysis pubis, menisci of knee joint

Calcification of fibrocartilaginous callus during bone repair)

Question 9

Steps of chondrogenesis

Answer 9

mesenchyme generates chondroblasts

chondroblasts secrete matrix, become isolated chondrocytes

chondroblasts replicate creating isogenous groups of chondrocytes

Question 10

interstitial growth

Answer 10

new cartilage formed within existing cartilage

Question 11

appositional growth

Answer 11

new cartilage formed at the surface of existing cartilage

Question 12

Extracellular matrix of Bone

Answer 12

Mineralized with calcium phosphate (hydroxyapatitecrystals)

type I collagen (primarily)

proteoglycans

glycoproteins (osteonectin, osteopontin)

bone-specific Vitamin K-dependent (osteocalcin, protein S)

growth factors & cytokines

Question 13

functions of bone

Answer 13

Structural support

Protection

Calcium regulation

Hemopoiesis

Question 14

Osteons (Haversian)

Answer 14

Cylindrical structural units of bone

Question 15

5 cell types in bone

Answer 15

Osteoprogenitor cells

Osteoblasts

Osteocytes

Bone-lining cells

Osteoclasts

Question 16

collagen fiber organization within bone

Answer 16

Collagen fibers are parallel within a lamella, but run different direction than adjacent lamella

( right → left, then, left → right)

Question 17

The canal in bone contains

Answer 17

blood supply

Question 18

Osteoprogenitor cell

Funtion, location

Answer 18

Function

Resting’ mesenchymal stem cell

• CBFA1 (core binding factor alpha-1) triggers differentiation into osteoblast

Location

Localized to external and internal surfaces of bone (periosteal and endosteal cells)

Question 19

Osteoblast

Funtion and location

Answer 19

Function

• bone forming cell
• secretes matrix = type I collagen (90% protein in bone)
• secretes vesicles that initiate matrix calcification

Location

• Single layer of cells opposed to forming bone
• gap junctions between osteoblasts

Question 20

Steps of bone matrix calcification

Answer 20

vesicles exocytosed from the osteoblast - contain alkaline phosphatase and pyrophosphatase → the initial site of mineralization

*elevated local extracellular Ca2+ and PO4 required (osteocalcin)

*crystallization of CaPO4 = hydroxyapatite crystals [Ca10(PO4)6(OH)2]

Question 21

osteocyte

Function and location

Answer 21

Maintians bone matrix

Mechanotransduction: sensing physical forces and translating them into biochemical responses

Found completely enclosed by bone matrix

processes extend thtough cannaliculi to connect w/ other osteocytes

Question 22

Bone lining cells

function and location

Answer 22

Function

provide nutritional support to help maintain osteoblasts

regulate Ca²⁺ and PO₄ movement

Location

develop from osteoblasts and line external (periosteal cells) and internal (endosteal cells) bone surfaces

gap junctions are found in between

Question 23

Osteoclast

Function and location

Answer 23

Function

Bone reabsorption

stimulated by parathyroid hormone and reduced by calcitonin

Location

Arise from fusion of mononuclear hematopoetic cells

Question 24

Steps of Osteoclast resorption

Answer 24

• A clear (sealing) zone adjacent to ruffled border is formed (integrins–actin)
• Free H+ from Carbonic acid (H2CO3) actively pumped out of cell.
• Acid environment causes breakdown of Ca10(PO4)6(OH)2 to

Ca2+, PO4, H2O
* Release of lysosomal enzymes (cathepsin K, matrix metalloproteinases) into extracellular space degrade protein component of bone matrix

• Osteoclasts ‘tunnel’ into existing bone, osteoblasts follow and rebuild