Unit 1 Topic 4

Question 1

Hyaline Cartilage

Answer 1

-found in articular surfaces, trachea, larynx, bronchi, epiphyseal plate, costal cartilage, and embryonic skeleton

Question 2

What percentage of hyaline cartilage is chondrocytes?

Answer 2

-5% is chondrocytes living in launae (where mature cells develop
-Nests: isogenous groups of chondrocytes; represent dividing chondrocytes; more active cells have more basophillic cytoplasm

Question 3

What percentage of extracellular matrix is in hyaline cartilage?

Answer 3

-95% extracellular matrix which is synthesized by chondrocytes and contains 3 classes of molecules

Question 4

What 3 classes of molecules are found in extracellular matrix?

Answer 4

-Collagen: primarily type III
-Proteoglycans and GAGS: use aggrecan to collect water
-Multi adhesive proteins: cell matrix interactions

Question 5

What percentafe of ECM is water and why?

Answer 5

• 60-80% of ECM due to the ability of GAGs to attract water which provides rigidity and flexibility

Question 6

What is extracellular matrix surrounded by?

Answer 6

-vascular/innervated by perichondrium
-composed of dense connective tissue (type I collagen) containing fibroblasts with chondrogenic cells

Question 7

Description of Elastic Cartilage

Answer 7

-found in pinna of ear and epiglottis
-high elastic fiber content allows deformation and return to original shape and type II collagen
-surrounded by perichondrium

Question 8

Description of Fibrocartilage

Answer 8

-found in interverbral disks, pubic symphysis, meniscus of knee joint; intermediate between DRCT and hyaline cartilage

Question 9

What are some features of fibrocartilage?

Answer 9

-similar to a tendon with chondrocytes
-withstands compression and sheering forces
-Matrix contains type I and type II collagen with different proteoglycans
-Cells include chondrocytes in lacunae and fibroblasts not in lacunae
-no perichondrium

Question 10

What types of collagen are found in hyaline cartilage?

Answer 10

primarily type II collagen

Question 11

What type of collagen is found in elastic cartilage?

Answer 11

type II collagen

Question 12

What types of collagen are found in fibrocartilage?

Answer 12

type I and II

Question 13

What are the matrix components of hyaline cartilage?

Answer 13

-95% ECM which contains
60-80% water, type III collagen, proteoglycans and GAGS (aggrecan), multiadhesive proteins for cell matrix interactions

Question 14

What are the matrix components of fibrocartilage?

Answer 14

contains type I and II collagen with different proteoglycans, cells incuding chondrocytes in lacunae and fibroblasts not in lacunae

Question 15

What types of cartilage has perichondrium?

Answer 15

-Hyaline: has perichondrium
-Elastic: has perichondrium
-Fibrocartilage: no perichondrium

Question 16

Interstital Cartilage Growth

Answer 16

division of cells and addition of ECM materials form within the cartilage (epiphyseal plate, isogenous groups and active chondrocytes

Question 17

Appositional Growth

Answer 17

surface growth by addition of new cells and ECM at the perichondrial surface (outside)

Question 18

Inorganic Components of Bone

Answer 18

~70% containing primarily hydroxyapatite crystals that are deposited on/around collagen fibers

Question 19

Organic Components of Bone

Answer 19

~30% containing collagen (~90% type I), proteoglycans/GAGs, and non-collagenous proteins

Question 20

What is the process of bone mineralization?

Answer 20

-Osteoid is secreted as organic ECM including osteocalcin (protein hormone that facilitates Ca2+ binding) and matrix vesicles \
-Ca2+ binds to secreted osteocalcin creating high extracellular Ca2+
-High Calcium stimulates osteoblasts to secrete alkaline phosphatase (ALP), which increases extracellular phosphate (PO4), further increasing extracellular Calcium
-Osteoblasts release matrix vesicles which contain ALP and pyrophosphatase, cleaving phosphate groups from nearby molecule in the matrix
-Calcium phosphate crystals to form
-This initiates matrix mineralization by the formation and deposition of hydroxyapatite crystals

Question 21

Progenitor Cells

Answer 21

-Derived from mesenchymal cells in the presence pf CBFA1/RUNX2 transcription factor
-Found on external (periosteum) and interal (endosteum) of bone surfaces
-Can differentiate into osteoblast

Question 22

Osteoblasts

Answer 22

-Differentiated cell secreting organic unmineralized matrix (osteoid) and alkaline phosphatase in membrane-bound vesicles to initiate mineralization

Question 23

Osteocytes

Answer 23

-Osteoblasts completely trapped in/surrounded by matrix it has secreted
-Reside in lacunae

Question 24

Osteoclasts

Answer 24

-Large, multinucleated cells that derive from mononuclear hematopoietic cells under the influence of RANK-RANKL signaling and dissolve bone matrix
-Found in the endosteum, and periosteum, and on internal surface of bone in indentations called Howship’s lacunae
-Ruffled border with microvilli-type structures that increase Surface Area for exocytosis of hydrolytic enzymes and secretion of protons
-The acidic microenvironment facilitates hydroxyapatite crystal breakdown
-Lysosomal enzymes and metalloproteinases break down organic matrix components

Question 25

Intramembranous Ossification

Answer 25

-formation of bone from a connective tissue sheath
-Condensation of embryonic and differentiation of mesenchymal cells into osteoprogenitor cell with further differentiation into osteoblasts
-Matrix mineralizes as bony spicules form and unite to form spongy bone trabeulae and eventually compact bone forms on the periphery

Question 26

Endochondral Ossification

Answer 26

erosion of hyaline cartilage model and replacement with bone

Question 27

What is the sequence of endochondral ossification?

Answer 27

-Development of hyaline cartilage model
-Growth of cartilage model.Formation of the bone collar on diaphysis by intramembranous ossification. Chondrocyte hypertrophy and calcification of diaphysis
-Developmental of primary ossification center in diaphysis. Vascular invasion in this region. Chondrocytes undergo hypertrophy and calcify their matrix. Bone tissue replaces calcified cartilage
-Development of the medullary cavity: Bone breakdown by osteoclasts forms the medullary cavity
-Development of secondary ossification centers : These occur in the epiphysis of the bone. Same process of bone replacing calcified cartilage
-Formation of articular cartilage and epiphyseal plate: Both structures consist of hyaline cartilage

Question 28

Zone of Reserve Cartilage

Answer 28

no cell division or active matrix production

Question 29

Zone of Proliferation

Answer 29

cells divide and organize into distinct columns and actively produce type II and type IX collagen along with other matrix proteins

Question 30

Zone of Hypertrophy

Answer 30

cells enlarge/accumulate glycogen. VEGF is released (which initiates vascular invasion) and production of type X collagen (serves as a scaffold for hypertrophied cartilage) increases. The matrix is compressed into linear bands between columns of hypertrophied cartilage cells that secrete alkaline phosphatase, initiating calcification

Question 31

Zone of Calcification

Answer 31

hypertrophied cells undergo apoptosis while matrix calcification increases

Question 32

Zone of Resorption/Vascular Invasion

Answer 32

small blood vessels invade, carrying osteoprogenitor cells from the perichondrium on their surface. These cells differentiate into osteoblasts and deposit osteoid on the surface of the cartilage spicules. Cartilage matrix is resorbed and more osteoid is deposited. Osteoblasrs become trapped in mineralized bone matrix, converting them to osteocytes. This primary bone is then remodeled by osteoclasrs into compact or spongy bone

Question 33

What is a mixed spicule?

Answer 33

calcified cartilage matrix and bone