Lecture 10

Question 1

List the 3 major types of cartilage and describe their locations

Answer 1

Hyaline Cartilage: external auditory meatus , larynx, tracheal cartilages, bronchial cartilages, fetal long bones, and articular ends of bones

Elastic Cartilage: auricle (pinna) of the ear and epiglottis

Fibrocartilage: intervertebral discs, pubic symphysis, insertion of some tendons and ligaments, and it is closely associated with dense CT or hyaline cartilage.

Question 2

What are the subdivisions of matrix types in hyaline cartilage? describe them

Answer 2

Appositional growth: growth in diameter (thickness) due to the addition of matrix on the peripheral cartilage surface

Interstitial growth: growth in length

Question 3

List the 3 types of bone tissue and describe them

Answer 3

Woven Bone: occurs during bone development and repair.
Produced rapidly in haphazard collagen foundation that has reduced structural integrity than other bone types

Spongy Bone: (trabecular/cancellous bone) has a 3D lattice of branching spicules that form trabecular surrounding the bone marrow spaces in long and flat bones

Compact bone: (lamellar bone) lacks cavities and forms the dense plate that covers the outside of long/flat bones

Question 4

What is the canalicular structure of compact bone? describe how lamellae, osteon, osteocyte, lacunae, haversian canal and volkman’s canals are related to this.

Answer 4

Has concentric (Haversian) lamellae that encircle an osteon (blood vessel and nerve). Osteocytes are found in lacunae that are connected to each other and the haversian canal via canaliculi. Volkman’s canals run perpendicular to haversian canals and connect them to each other and the surface of the bone.

Question 5

Define Sharpey’s fibers

Answer 5

Sharpey’s fibers: collagen fibers derived from the outer layer of the periosteum, that project into the outer circumferential lamellar system

Question 6

Define Periosteum

Answer 6

Periosteum: formed by 2 layers

the outer layer that contains abundant collagen fibers and blood vessels that penetrate the Volkmann’s canals

the inner layer that contains osteoprogenitor cells.

Question 7

List the 4 types of cells involved in bone formation, maintenance, and reabsorption

Answer 7

Osteoblast

Osteocyte

Osteoclast

Osteoprogenitor Cells

Question 8

Define Osteoblast and describe it’s activity(s)

Answer 8

secretes bone matrix by way of secreting collagen and catalyzing the mineralization (incorporation of hydroxyapetite)

Question 9

Define Osteocyte and describe it’s activity(s)

Answer 9

maintains bone matrix by helping control Calcium and phopshate levels in the matrix. Derived from osteoblasts and are trapped by the matrix they secrete.

Question 10

Define Osteoclast and describe it’s activity(s)

Answer 10

remodels bone through resorption (this “cuts” into bones)

Question 11

Define Osteoprogenitor cells and describe their activity(s)

Answer 11

cells derived from mesenchyme of the embryonic somite and posses mitotic potential. These are stem cells that give rise to osteoblasts and bone lining cells found in the inner portions of the periosteum, endosteum, and inside the vascular canals of compact bone.

Question 12

High PTH levels _________ and low PTH levels _________ , because PTHis the primary regulator of bone turnover.

Answer 12

stimulates osteoblasts to release osteoclast-differentiation factors

stimulates bone formation by osteoblasts is stimulated.

Question 13

Where are osteoclasts derived from? in what location in the body are these precursors found?

Answer 13

Osteoclasts are derived from monocyte (a type of macrophage) lineage that originates from monocyte precursors in the bone marrow

Question 14

what is osteitis fibrosa? what is it caused by?

Answer 14

a condition that causes very weak bones due to bone erosion and fibrosis caused by high levels of PTH.

Question 15

What are the 2 major products secreted by osteoclasts involved in bone reabsorption? what do they do?

Answer 15

Cathepsin K: a lysosomal protease that can catabolize elastin, collagen, and gelatin

H+ Cl- ions: dissolve the inorganic matrix of bone

Question 16

describe the biochemical mechanism by which osteoclasts absorb bone.

Answer 16

1. Actin filaments accumulate to form a sealing zone (with integrin and osteopontin) around the circumference of the ruffled border of the osteoclast
2. A Cl- channel prevents an excessive rise in intracellular pH
3. Bicarbonate is exchanged for Cl-, which is then moved into Howship’s lacuna via Cl- channels. This step ensures cytoplasmic electroneutrality.
4. Carbonic anhydrase II creates protons from CO2 and H20 that are then pumped into Howship’s lacuna by H+ ATPase pumps. This degrades the mineral inorganic bone matrix.
5. Cathepesin K and MMP-9 (metalloproteinase-9) are released into H’s lacuna to degrade the organic bone matrix (type I collagen and noncollagenous proteins)

Question 17

During osteoclast activity, why is bicarbonate exchanged for Cl- in the osteoclast?

Answer 17

to ensure electroneutrality of the cell

Question 18

Cathepsin and MMP-9 do what when released by osteoclasts?

Answer 18

they degrade the organic bone matrix (type I collagen and noncollagenous proteins)

Question 19

What does carbonic anhydrase II do in an osteoclast?

Answer 19

creates protons from CO2 and H2O that will be pumped into the Howship’s lacuna to degrade the mineral component of bone matrix.

Question 20

Differentiate between territorial and inter-territorial matrix.

Answer 20

territorial matrix surrounds each chondrocyte and has a high glycosaminoglycan content and low collage content

Inter-territorial matrix surrounds the territorial matrix and has a low glycosaminoglycan content and a high collagen content

Question 21

What type of fibers are found in hyaline cartilage?

Answer 21

type II collagen fibers

Question 22

what type of collagen does fibrocartilage contain? does it have a perichondrium?

Answer 22

no (it has type I) ; no

Question 23

True or false: haversian systems include the periosteum of that area of bone.

Answer 23

false, haversian systems never include the periosteum

Question 24

What does parathyroid hormone stimulate osteoblasts to secrete/express or stop secreting/expressing?

Answer 24

PTH stimulates the expression of RankL and the secretion of M-CSF

PTH stops the expression of osteoprotegrin