Day 5: Bone + Cartilage Flashcards
1
Q
cartilage matrix
A
- dense random feltwork of type II collagen fibrils (50%)
- ground substance
- water
- (50%) proteoglycans (aggregan) and adhesive glycoproteins
- aggrecan (glycosaminoglycan, -) binds collagen (+) fibrils…
- attracts Na+ , which attracts H2O
- providing turgor and ability to resist compression
2
Q
classifications of cartilage
A
hyaline:
- homogenous matrix, no visible fibers
- perichondrium
- chondrocytes dispersed in highly hydrated, fiber-reinforced solid
elastic:
- increased flexibility and elasticity
- elastic fibers added to cartilage matrix, high cellular density
- examples: outer ear, eustachian tube, epiglottis
fibrocartilage:
- intermediate form between hyaline cartilage and dense connective tissue; prominent type I collagen fibers in the matrix
- increased tensile strength, with stiffness and resiliency of cartilage
- typically a transition tissue, no perichondrium
3
Q
territorial matrix of cartilage
A
more hydrated, immediately surrounding chondrocytes, more aggrecan
4
Q
interterritorial matrix of cartilage
A
more structural support, between chondrocytes and isogenous groups, more type II collagen
5
Q
cartilage growth
A
- mesenchymal cells differentiate into chondroblasts
- chondroblasts withdraw their processes and cluster as “centers of chondrification”
- chondroblasts secrete matrix and become dispersed
- interstitial and appositional growth follows
-
interstitial growth:
- chondroblasts produce daughter cells by mitosis
- form isogenous groups of cells, each secreting small amount of matrix and become dispersed
- occurs for small post natal period, except in epiphyseal plate
-
appositional growth:
- chondroblasts develop from progenitor cells of the inner perichondrium, add matrix to the surface of the cartilage
6
Q
advancing age and cartilage
A
- reduced ability of chondrocytes to maintain ECM, synthesis decreases and proteoglycans (aggrecans) are smaller
- reduced responsiveness to growth factors
- little or no cell division or cell death in normal adult articular chondrocytes; no ready supply of progenitor cells
7
Q
repair of cartilage
A
- repair is poor, except in children
- wound is often repaired by fibrous connective tissue
some therapeutic techniques:
- transplant chondrogenic cells with perichondrium from another site
- remove chondrocytes, culture in vitro, transplant back
- transplant tissue-engineered synthetic matrix or xenographs
- transplant chondroblasts differentiated from adult stem cells
- nutri-ceudicals (chondrosamine, chondroitin sulfate, etc)
8
Q
molecular composition of adult bone
A
- matrix: 10% H2O, 45% organic, 45% mineral (by volume)
- Organic matrix:
- 95% type I collagen
- 5 % glycoproteins (osteonectin, osteopontin, etc)
- mineral is crystals of hydroxyapatite Ca10(PO4)6(OH)2
- Organic matrix:
- hydroxyapatite crystals are initially deposited within the collagen fibrils, and surround the fibrils as matrix becomes more densely calcified
9
Q
macroscopic organization of bone
A
two types:
- Spongy (trabecullar, cancellous)
- 3D lattice of interconnected rods, plates, and arches with many open spaces
- Compact (dense, cortical)
- lacks wide spaces and trabeculae
10
Q
osteoblasts
A
- principal cells of bone formation; don’t undergo mitosis
- polygonal cells on the free surface of bone
- interconnected laterally with gap junctions
- bone growth only occurs by apposition
- synthesize osteoid that is subsequently mineralized and becomes bone
- osteoblasts become osteocytes
11
Q
osteocyte
A
- bone surrounds osteocytes, osteoblasts become osteocytes
-
osteocytes:
- capable of producing osteoid
- capable of bone resorption (osteocytic osteolysis)
- manage the bone’s reservoir of calcium
- can change polarity and secrete matrix on their free surface, or stop producing matrix (becoming trapped in lacunae, and grow processes
- although embedded in bone, can contact each other with gap junctions at tips of processes (canaliculi) connecting the lacunae
- mechanical sensors:
- sense formation of bone, adjusts its structure to adapt to mechanical pressures in the environment
- osteocytes interconnect with other osteocytes, osteoblasts, and blood vessels
12
Q
bone lining cells
A
- squamous, quiescent cells
- cover all surfaces not covered with osteoblasts
- provide a selective barrier between bone and tissue fluid
- can be reactivated into osteoblasts as needed
13
Q
osteoprogenitor cells
A
- partially differentiated, bi potential mesenchymal stem cells capable of mitotic division and transformation into osteoblasts
- reside in 3 locations:
- inner cellular layer (cambium) of periosteum
- in bone marrow cavity adjacent to cells of the endosteum
- within haversian canals
14
Q
osteoclasts
A
- large multinucleated (polykaryon) cells specialized for bone resorption
- forme by asynchronous fusion of monocyte progenitor cells
- appear within Howship’s lacunae
- (subosteoclastic compartment, resorption bay)
-
polarized cells with 3 regions:
- ruffled border: on face of osteoclast adjacent to bone, membrane with proton pumps to pump H+ into subosteoclastic compartment (Howship’s lacuna) and Cl- channels
-
clear/sealing zone: (encircles the osteoclast where is sits on the bone surface); devoid of organelles but rich in actin and has integrins in plasmalemma
- allows osteoclasts to become sealed to bone
- antiresorptive surface/basal zone: the plasmalemma (on side away from ruffled border) contains Cl-/HCO3- anion exchange channels that serve to maintain the proper intracellular ionic balance
15
Q
osteoclast: bone resorption
A
- intracellular carbonic anhydrase located near ruffled border: produces H+ and HCO3-
- HCO3- and Cl- exchange
- H+ and Cl- pumped into Howship’s lucuna
- produces pH 4.5
- Mineral removed by acid environment
- Organic component degraded by lysosomal cathepsins
- Collagenases and metalloproteinases are secreted into the subosteoclastic compartment
16
Q
comparison of hyaline cartilage and lamellar bone
A
