Bone and cartilage

Question 1

1. For cartilage, describe its cellular and extracellular composition, its structural properties, and how it is organized. State the functions of cartilage tissue.
2. Describe how cartilage grows during fetal and child development.
3. State the characteristics that distinguish the three basic types of cartilage.
4. State the different cell types found in bone. For each cell type, describe their functions, their origins, and describe how they are organized in bone tissue.
5. Describe the composition of bone extracellular matrix, the functions of the different components, where these extracellular matrix components are made, and how they are deposited to form bone matrix.
6. Describe the two different processes that lead to bone formation and how long bones grow in length and in width.
7. Describe the sequence of events that occur in bone remodeling.
8. Describe how bone formation and remodeling is regulated.
9. Describe how defects in bone remodeling leads to disease.
10. Describe how calcium is deposited and resorbed from bone matrix, and how regulation of bone cells controls the levels of blood calcium.

Answer 1

xx

Question 2

Fxn of skeletal system (4):

Answer 2

1. Protection for critical organs (e.g. the ribs for the heart and lungs, the skull for the brain)
2. Mechanical support for locomotion; by supporting and providing attachments for muscles and joints for flexible movement.
3. Calcium and phosphate homeostasis: Bone is a tightly regulated reservoir of calcium for the entire body.
4. To house, protect, and regulate the stem cell precursors of blood cells (the hematopoietic system) (a function of bone).

Question 3

Fxn of cartilage

Answer 3

(1) to provide a resilient but pliable support structure.

(2) to direct the formation and growth of bone.

Question 4

Chondrocytes

Answer 4

make cartilage matrix and tissue. During cartilage growth, chondrocytes are proliferative and secrete the components of the cartilage extracellular matrix (ECM)

Question 5

What three molecules control calcium homeostasis and in what way?

Answer 5

Calcitonin - stimulates calcium uptake into bone
Parathyroid hormone - stimulates bone resorption (liberation of Ca from bone)
Vitamin D - Uptake of Ca from intestines

Question 6

Hyaline cartilage (4)

Answer 6

contains collagen that forms relatively thin fibrils that are generally arranged in an irregular three dimensional pattern.

a. Allows metabolites to readily diffuse through the tissue.
b. Promotes resiliency to compression forces during joint movement.
c. Allows growth of chondrocytes and matrix from within the matrix.
d. During growth, it can calcify and attract cell that initiate bone formation.

Question 7

Elastic cartilage

Answer 7

distinguished by abundant elastic fibers and interconnecting sheets (lamellae) of elastic material.

+found in the external ear, in the epiglottis, and the larynx.
+under normal circumstances, does not calcify.

Question 8

Fibrocartilage

Answer 8

contains large bundles of regularly arranged collagen that is very similar to dense regular connective tissue

found as a continuation of dense regular connective tissue where tendons attach to bones, and also in the intervertebral discs

designed to resist compression and sheer forces.

Question 9

diaphysis

Answer 9

A long bone consists of a central shaft, the diaphysis,

Question 10

epiphysis

Answer 10

A long bone consists of a central shaft, the diaphysis, and two expanded ends, each called an epiphysis.

Question 11

compact bone

Answer 11

aka cortical bone. The hardened exterior of bone

Question 12

trabecular bone

Answer 12

aka spongy or cancellous. trabeculae provide extensive surface area for metabolism

Question 13

bone marrow

Answer 13

Within the spaces between the trabeculae of the inner spongy bone is soft tissue called bone marrow

Question 14

Bone marrow consists of either ____ or ______.

Answer 14

hematopoietic tissue (red bone marrow) or adipose cells (white bone marrow)

Question 15

periosteum

Answer 15

The outer surface covering the bone called the periosteum, which contains dense connective tissue containing fibroblasts, bone precursors and bone cells.

Question 16

endosteum

Answer 16

The inner surface where trabeculae contact internal soft tissue is called the endosteum

Question 17

Osteoprogenitor cells

Answer 17

are stem cells that are capable of cell division to generate the osteoblasts and osteocytes that comprise most of the cells of bone.

Osteoprogenitors are present in both the periosteal and endosteal surfaces, and in the soft connective tissue of the channels.

Question 18

Osteoblasts

Answer 18

line the inner layers of both periosteal and endosteal surfaces where bone growth or remodeling is occurring. Osteoblasts are capable of cell division.

These cells actively secrete the initial un-mineralized extracellular matrix of bone, which is called OSTEOID.

Question 19

Osteoblasts also pinch off membrane-enclosed vesicles, the _____, which contain enzymes that initiate bone calcification (mineralization) (see below).

Answer 19

matrix vesicles

Question 20

Osteocytes

Answer 20

are directly derived from osteoblasts. osteocytes extend long processes through tiny channels, called canaliculi, in the calcified matrix; these processes form gap junctions with processes from other osteocytes.

he role of osteocyte activity in bone maintenance is not clear, but they probably send signals to each other and to osteoblasts at the surface through their gap junctions.

Question 21

Osteoclasts are not related by lineage to the above bone cells and have a unique function.

Answer 21

Osteoclasts are derived from monocytes in the blood, which themselves originate from hematopoietic stem cells in the bone marrow. They resemble and are related to macrophages.

Question 22

(5) fxn of osteoclasts

Answer 22

1) degrade bone matrix
2) degrade cartilage matrix
3) calcium mobilization
4) angiogenesis
5) nerve growth

Question 23

Bone matrix:

Answer 23

Most extracellular matrix in bone is calcified and packed with dense parallel collagen fibers.

Question 24

hydroxyapatite

Answer 24

Unlike most connective tissues, bone matrix is unique in containing large amounts of a crystallized form of Ca2+ and PO4 called hydroxyapatite [Ca10(PO4)6(OH)2], the crystals of which are found on collagen fibers, and in the ground substance; i.e. the matrix is mineralized or calcified.

Question 25

Haversian canals

Answer 25

channels that traverse the long axis through compact bone

Question 26

osteon

Answer 26

Bone lamellae tend to surround a Haversian canal in concentric rings (like the rings of a tree); these lamellae and their canal are frequently referred to as a unit called the osteon

Question 27

Volkmann’s canals

Answer 27

link Haversian canals to each other and to the periosteum at the bone surface.

Question 28

Where are the mesenchymal stem cells located?

Answer 28

In the perichondrium.

Question 29

Appositional vs interstitial growth

Answer 29

Growth at surface vs growth from within (mesenchymal vs chondrocytes in lacunae)

Question 30

MSC–> osteoprogenitor—>

Answer 30

osteoblasts

Question 31

Osteoid

Answer 31

initial secretion of osteoblasts

Question 32

Osteocytes are quiescent cells that don’t divide or secrete much. They have a function that is mostly sensory/regulatory.

Answer 32

ok, so bone can only grow by appositional growth? Yes, that is correct. how do long bones grow then? why, it’s the interstitial growth of chondrocytes!

Question 33

Osteoblasts secrete matrix vesicles which are filled with?

Answer 33

Ca and Po4–hydroxyapatite.

Question 34

What is the origin of osteoclasts?

Answer 34

hematopoetic (monocytes–>osteoclasts)

Question 35

What is intramembranous ossification? What structures are formed this way?

Answer 35

direct formation of bone from connective tissue (flat bones, skull, eg)

Question 36

Endochondral ossification

Answer 36

within cartilage ossification. All long bones are formed this way.

1) developmental transformation from cartilage producing lineage to osteo producing lineage
2) calcification of cartilage matrix - hypertrophy
3) recruitment of osteoclasts which degrade calcified cartilage matrix, bring with them the nerves, blood vessels, etc

Question 37

What adds length to long bone?

Answer 37

interstitial growth of chondrocytes.

Question 38

Groups of chondroctyes within a lacuna or still close together are actually clones of cells derived from mitosis and are called ______ (of clonal origin).

Answer 38

isogenous groups