Connective Tissue 2

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.

Answer 1

-Cartilage isn’t very dynamic, is avascular, and has limited ability for its repair, but is necessary for conversion into bone.
2 main functions:
-Provide resilient and pliable support
-Direct formation/growth of bone.
-Only articular surfaces of bone retain cartilage tissue, as well as in ear, nose, tendons etc.

-Chondrocytes (from mesenchymal cells) form cartilage (cartilage can also come from external layer of CT = perichondrium).
-Perichondrium –> new chondrocytes.
Chondrocytes are proliferative and secrete components of ECM; eventually become surrounded and isolated in a lacuna.
-Chondrocytes secrete special ECM that contains 3 types of cartilage:

• Hyaline cartilage –>
• Formed in thin fibrils arranged in irregular 3D pattern; -Rich in proteoglycans and hyaluronic acid –> allows for hydration and flexibility.
• Lets metabolites readily diffuse
• promotes resiliency to compression forces
• allows growth of chondrocytes
• can calcify and cause bone formation.
• Elastic cartilage–>
• Also has thin collagen fibrils and proteoglycans, but also has elastic fibers and interconnecting sheets (lamellae) of elastic material.
• Designed for elasticity so does not calcify.
• Fibrocartilage–>
• large collagen bundles;
• basically is a continuation of dense connective tissue where tendons attach bones and also in intervertebral discs.
• Because cartilage is avascular, gets nutrients and metabolites via diffusion through perichondrium. -Facilitated by the hydrated GAGs.

Question 2

2. Describe how cartilage grows during fetal and child development.

Answer 2

• Chondrocytes arise from mesenchymal cells.
• Fetal skeleton is mostly cartilage that gets replaced by bone.
• Cartilage can grow via appositional growth (growth at the surface via the perichondrium) or interstitial growth (from within, in which they proliferate within their lacunae and secrete ECM  internal growth).

Question 3

3. State the characteristics that distinguish the three basic types of cartilage.

Answer 3

on another card

Question 4

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.

Answer 4

Flat bones = skull, mandible, and long bones = the other ones.

• Long bones have the central diaphysis shaft and the epiphysis ends.
• Outer cortical region = solid = compact bone.
• Inner portion is spongy and has trabeculae = cancellous/trabecular bone.
• Compact bone provides strength whereas trabeculae provide surface area for metabolism.
• Spaces in spongy bone = bone marrow, can contain hematopoietic tissue or adipose cells.
• Outer surface of bone = periosteum (contains dense connective tissue) and inner surface = endosteum (where Ca mobilization and storage happens). Channels through bone contain vessels, nerves, etc.

1) Osteoprogenitor cells = stem cells that give rise to osteoblasts and osteocytes. Present in periosteal and endosteal surfaces.
2) Osteoblasts = inner layers of perioseal and endosteal surfaces; secrete osteoid matrix and pinch off matrix vesicles that contain enzymes that initiate bone calcification. They are connected to each other via gap junctions and are capable of cell division.
3) Osteocytes = derived from osteoblasts. Become encased by bone matrix in lacuna and arrest in Go. Extend long processes (canaliculi) and they form gap junctions with other processes. Results in an interconnected lattice of cells. Some ability to modify bone matrix, but don’t secrete much.
4) Osteoclasts not related by lineage (derived from monocytes, which arise from hematopoietic stem cells). They are phagocytic and degrade bone or cartilage matrix to allow inward growth of vessels. Also resorb already made bone to  remodeling, and mobilize Ca into blood stream.

Question 5

5. Describe the composition of bone extracellular matrix, and the functions of the different components discussed in class and lecture notes. Describe where these extracellular matrix components are made, and how they are deposited to form bone matrix.

Answer 5

• Most bone matrix is calcified and packed with dense parallel collagen fibers.
• Contain hydroxyapatite crystals (of Ca and PO4) (so the matrix is mineralized/calcified).
• Bone is vascularized and innervated because it has Haversian canals that traverse the bone.
• Lamellae surround Haversian canals in rings = osteon.
• Volkmann’s canals link H. canals to each other and the periosteum.
• Also contains negatively charged proteoglycans and proteins.