Ims: Histo Block 1 Lecture 3A

Front 1

What is the germ layer origin of cartilage?
Where is it located?
What are its functions?

Back 1

Mesoderm (except some parts of skull)

Articular surfaces, trachea, nose, ear, epiglottis

Shock absorber, cushioning support, articular surfaces

Front 2

What does cartilage consist of?

Back 2

AVASCULAR matrix with chondrocytes situated within lacunae; surrounded by perichondrium or synovial fluid

Front 3

What is the purpose of perichondrium and synovial fluid in cartilage? What is required of the matrix?

Back 3

both provide nutrients for cartilage bc cartilage is AVASCULAR

Matrix must permit diffusion

Front 4

Describe appositional growth.

Back 4

Adding cells to area that will become cartilagenous; you appose cells (accrue them)

Forms from mesenchyme; surface growth occus between perichondrium and previously formed cartilage

Chondrogenic cells of perichondrium become chondroblasts and start to create cartilage at boundaries of structure

New chondrocytes surround themselves with matrix and within lacunae

Front 5

Describe interstitial growth.

Back 5

Occurs within cartilage

Young chondrocytes proliferate (mitotic) and actively synthesize matrix material generating clusters of cells that are pushed apart by new matrix.

Front 6

What are the three types of cartilage? Briefly describe each.

Back 6

Hyaline - most ubiquitous; most joints, all resp (except epiglottis), nasal

Elastic - lots of elastin fiber in matrix; epiglottis, pinna of ear

Fibrocartilage - tough; ~dense regular CT. found in certain jts, intervertebral discs

Front 7

What is hyaline cartilage comprised of?

Back 7

Collagen II,

hyaluornic acid, PGs

Front 8

How would you identify hyaline cartilage on a slide?

Back 8

Glassy quality to cells; collagen fibers not visible, no blood vessels

Front 9

What is the germ layer origin of bone?

What is the function of bone?

Back 9

mesoderm (or neural crest in case of cranial bones)

protect visceral organs; muscle attachment site; calcium depot in bony matrix;

Front 10

What occurs in bone marrow?

Back 10

hematopoiesis (blood cell production)

Front 11

Contrast axial and appendicular skeleton.

Back 11

Axial: torso, head (cranium, rib cage, vertebral column)
Appendicular: things for limbs

Front 12

Describe cells and vascularization of bone.

Back 12

Osteocytes sequestered in lacunae

Matrix is vascularized; UNABLE to allow diffusion

Front 13

Contrast primary bone with secondary bone.

Back 13

Primary Bone: first type of bone formed developmentally; it is spongy, not mineralized

Primary bone later replaced by secondary (mature) bone which can be EITHER compact or cancellous (spongy)

Front 14

Contrast compact with spongy bone.

Back 14

Compact (aka Cortical or Dense):
made up of osteons, ~80% of skeletal system

Spongy (Cancellous or Trabecular):
no Haversian systems, lattic of thin trabeculae with marrow spaces (hematopoietic activity in these cavities)
Found in flat bones of skull, sternum, and in epiphyses of long bones

Front 15

Contrast Volkmann's canals with Haversian canals.

Back 15

Volkmann's canals have BV's entering periosteum and endosteum perpendicularly to Haversian canals that they interconnect.

AKA Perforating canals

Front 16

What are canaliculi?

Back 16

Thin canals radiating from lacunae which connect adjacent lacunae, eventually connecting with central canal; it's how stuff from blood accesses osteocytes

Front 17

What function do osteocyte processes serve?

Back 17

Processes protrude into radiating canals to meet with other processes via gap jns; this allows communication and nutrient exchange

Front 18

Briefly describe how osteocytes form. Begin with mesenchyme.

Back 18

Osteoprogenitor cells form from mesenchyme (mesoderm mostly)

Differentiate into osteoblasts that secrete organic material of matrix (collagen, proteoglycans, glycoproteins)

Once surrouned in matrix, they are osteocytes within lacunae

Front 19

Where do osteoclasts form from? What's their role?

Back 19

Blood monocytes, resorb bony matrix, and release Ca++ from it.

Front 20

Via what mechanism (general) do osteoclasts work?

Back 20

Secrete enzymes; DON'T PHAGOCYTOSE

Front 21

When does an osteoblast become an osteocyte?

Back 21

When it stops secreting matrix.

Front 22

Which side of an osteoclast faces the bony matrix?

Back 22

Side with ruffles.

Front 23

What cells are osteoclasts derived from? Describe their nucleus.

Back 23

macrophage-derived from monocytes

MULTINUCLEATE

Front 24

How does the size of an osteoclast compare with the size of an osteoblast?

Back 24

Osteoclasts are huge!

Front 25

What is the organic:inorganic ratio of bone matrix? What comprises each component?

Back 25

50:50

Organic: 95% Type 1 collagen, amorphous ground substance
Glycoproteins that help bind calcium (glycoprots = cyaloprotein and osteocalcin)

Inorganic: Ca 2+, Phosphorus, bicarb, nitrate, Mg 2+, K+, Na+, hydroxyapatite crystals; formed of calcium and phosphorus

Front 26

How would a keratinized cell look on a slide?

Back 26

Thick layer of dead cells at top

Front 27

Describe intramembranous ossification. In what kind of bone does it occur?

Back 27

Mesenchymal cells condense to form a primary ossification center.

Osteoblasts differentiate and begin secreting osteoid. When the osteoblasts become trapped in matrix, become mature osteocytes.

Bony trabeluae (fused spicules) then join together to form spongy bone.

Occurs in dermal bones (flat bones, cranial bones, clavicles) and in initial stages of endochondral ossification

Front 28

Describe endochondral ossification. Where does it occur?

Back 28

Replacement of hyaline cartilage with bone

All skeletal bones below skull (except clavicles)

Front 29

Describe the steps of endochondral ossification.

Back 29

Primary Ossificiation:
Mainly appears during fetal dev't;
Begins with hyaline cartilage at mid-diaphysis
Osteoclasts etch holes in bone to permit osteogenic cells and BV's to penetrate cartilage model
Osteoblasts elaborate bone matrix on degenerating cartilage core
Subperiosteal bone becomes thicker and elongates toward epiphyses

Secondary Ossification: Occurs after birth and forms epiphyses of long bones, and parts of irregular/flat bones

Diaphysis and epiphyses separated by growing zone of cartilage known as Epiphyseal plate.

Front 30

What are the 5 distinct ossification zones of the epiphyseal plate? Describe what occures at each zone.

Back 30

Resting Cartilage (inactive chondrocytes)
Proliferating cartilage (chondrocytes multiplying; main area for bone growth)
Hypertrophic Zone: chondrocytes secrete alkaline phosphate
Calcifying Zone: (degenerating cartilage) matrix around hypertrophied chondrocytes traps cell in matrix; chondrocytes begin dying
Ossification Zone: calcification (degradation of chondrocytes) complete due to lack of nutrients; new osteoblasts recruited into calcified cartilage; they deposit bone proteins into matrix